rfc9350.original   rfc9350.txt 
Network Working Group P. Psenak, Ed. Internet Engineering Task Force (IETF) P. Psenak, Ed.
Internet-Draft Cisco Systems, Inc. Request for Comments: 9350 Cisco Systems, Inc.
Intended status: Standards Track S. Hegde Category: Standards Track S. Hegde
Expires: 20 April 2023 Juniper Networks, Inc. ISSN: 2070-1721 Juniper Networks, Inc.
C. Filsfils C. Filsfils
Cisco Systems, Inc. Cisco Systems, Inc.
K. Talaulikar K. Talaulikar
Cisco Systems, Inc Cisco Systems, Inc
A. Gulko A. Gulko
Edward Jones Edward Jones
17 October 2022 February 2023
IGP Flexible Algorithm IGP Flexible Algorithm
draft-ietf-lsr-flex-algo-26
Abstract Abstract
IGP protocols historically compute best paths over the network based IGP protocols historically compute the best paths over the network
on the IGP metric assigned to the links. Many network deployments based on the IGP metric assigned to the links. Many network
use RSVP-TE based or Segment Routing based Traffic Engineering to deployments use RSVP-TE or Segment Routing - Traffic Engineering (SR-
steer traffic over a path that is computed using different metrics or TE) to steer traffic over a path that is computed using different
constraints than the shortest IGP path. This document specifies a metrics or constraints than the shortest IGP path. This document
solution that allows IGPs themselves to compute constraint-based specifies a solution that allows IGPs themselves to compute
paths over the network. This document also specifies a way of using constraint-based paths over the network. This document also
Segment Routing (SR) Prefix-SIDs and SRv6 locators to steer packets specifies a way of using Segment Routing (SR) Prefix-SIDs and SRv6
along the constraint-based paths. locators to steer packets along the constraint-based paths.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on 20 April 2023. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9350.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 2. Requirements Language
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Terminology
4. Flexible Algorithm . . . . . . . . . . . . . . . . . . . . . 5 4. Flexible Algorithm
5. Flexible Algorithm Definition Advertisement . . . . . . . . . 6 5. Flexible Algorithm Definition Advertisement
5.1. IS-IS Flexible Algorithm Definition Sub-TLV . . . . . . . 6 5.1. IS-IS Flexible Algorithm Definition Sub-TLV
5.2. OSPF Flexible Algorithm Definition TLV . . . . . . . . . 8 5.2. OSPF Flexible Algorithm Definition TLV
5.3. Common Handling of Flexible Algorithm Definition TLV . . 10 5.3. Common Handling of the Flexible Algorithm Definition TLV
6. Sub-TLVs of IS-IS FAD Sub-TLV . . . . . . . . . . . . . . . . 11 6. Sub-TLVs of IS-IS FAD Sub-TLV
6.1. IS-IS Flexible Algorithm Exclude Admin Group Sub-TLV . . 11 6.1. IS-IS Flexible Algorithm Exclude Admin Group Sub-TLV
6.2. IS-IS Flexible Algorithm Include-Any Admin Group 6.2. IS-IS Flexible Algorithm Include-Any Admin Group Sub-TLV
Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.3. IS-IS Flexible Algorithm Include-All Admin Group Sub-TLV
6.3. IS-IS Flexible Algorithm Include-All Admin Group 6.4. IS-IS Flexible Algorithm Definition Flags Sub-TLV
Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . . 13 6.5. IS-IS Flexible Algorithm Exclude SRLG Sub-TLV
6.4. IS-IS Flexible Algorithm Definition Flags Sub-TLV . . . . 14 7. Sub-TLVs of the OSPF FAD TLV
6.5. IS-IS Flexible Algorithm Exclude SRLG Sub-TLV . . . . . . 16 7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV
7. Sub-TLVs of OSPF FAD TLV . . . . . . . . . . . . . . . . . . 17 7.2. OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV
7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV . . . 17 7.3. OSPF Flexible Algorithm Include-All Admin Group Sub-TLV
7.2. OSPF Flexible Algorithm Include-Any Admin Group 7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV
Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . . 17 7.5. OSPF Flexible Algorithm Exclude SRLG Sub-TLV
7.3. OSPF Flexible Algorithm Include-All Admin Group 8. IS-IS Flexible Algorithm Prefix Metric Sub-TLV
Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . . 18 9. OSPF Flexible Algorithm Prefix Metric Sub-TLV
7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV . . . . 19 10. OSPF Flexible Algorithm ASBR Reachability Advertisement
7.5. OSPF Flexible Algorithm Exclude SRLG Sub-TLV . . . . . . 20 10.1. OSPFv2 Extended Inter-Area ASBR LSA
8. IS-IS Flexible Algorithm Prefix Metric Sub-TLV . . . . . . . 21 10.1.1. OSPFv2 Extended Inter-Area ASBR TLV
9. OSPF Flexible Algorithm Prefix Metric Sub-TLV . . . . . . . . 22 10.2. OSPF Flexible Algorithm ASBR Metric Sub-TLV
10. OSPF Flexible Algorithm ASBR Reachability Advertisement . . . 23 11. Advertisement of Node Participation in a Flex-Algorithm
10.1. OSPFv2 Extended Inter-Area ASBR LSA . . . . . . . . . . 23 11.1. Advertisement of Node Participation for Segment Routing
10.1.1. OSPFv2 Extended Inter-Area ASBR TLV . . . . . . . . 25 11.2. Advertisement of Node Participation for Other Data Planes
10.2. OSPF Flexible Algorithm ASBR Metric Sub-TLV . . . . . . 26 12. Advertisement of Link Attributes for Flex-Algorithm
11. Advertisement of Node Participation in a Flex-Algorithm . . . 28 13. Calculation of Flexible Algorithm Paths
11.1. Advertisement of Node Participation for Segment 13.1. Multi-area and Multi-domain Considerations
Routing . . . . . . . . . . . . . . . . . . . . . . . . 28 14. Flex-Algorithm and Forwarding Plane
11.2. Advertisement of Node Participation for Other 14.1. Segment Routing MPLS Forwarding for Flex-Algorithm
Data-planes . . . . . . . . . . . . . . . . . . . . . . 28 14.2. SRv6 Forwarding for Flex-Algorithm
12. Advertisement of Link Attributes for Flex-Algorithm . . . . . 29 14.3. Other Data Planes' Forwarding for Flex-Algorithm
13. Calculation of Flexible Algorithm Paths . . . . . . . . . . . 30 15. Operational Considerations
13.1. Multi-area and Multi-domain Considerations . . . . . . . 31 15.1. Inter-area Considerations
14. Flex-Algorithm and Forwarding Plane . . . . . . . . . . . . . 34 15.2. Usage of the SRLG Exclude Rule with Flex-Algorithm
14.1. Segment Routing MPLS Forwarding for Flex-Algorithm . . . 34 15.3. Max-Metric Consideration
14.2. SRv6 Forwarding for Flex-Algorithm . . . . . . . . . . . 35 15.4. Flexible Algorithm Definition and Changes
14.3. Other Data-planes' Forwarding for Flex-Algorithm . . . . 36 15.5. Number of Flex-Algorithms
15. Operational Considerations . . . . . . . . . . . . . . . . . 36 16. Backward Compatibility
15.1. Inter-area Considerations . . . . . . . . . . . . . . . 36 17. Security Considerations
15.2. Usage of SRLG Exclude Rule with Flex-Algorithm . . . . . 37 18. IANA Considerations
15.3. Max-metric consideration . . . . . . . . . . . . . . . . 37 18.1. IGP IANA Considerations
15.4. FAD Definition and Changes . . . . . . . . . . . . . . . 38 18.1.1. IGP Algorithm Types Registry
15.5. Number of Flex-Algorithms . . . . . . . . . . . . . . . 38 18.1.2. IGP Metric-Type Registry
16. Backward Compatibility . . . . . . . . . . . . . . . . . . . 38 18.2. IGP Flexible Algorithm Definition Flags Registry
17. Security Considerations . . . . . . . . . . . . . . . . . . . 38 18.3. IS-IS IANA Considerations
18. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39 18.3.1. IS-IS Sub-TLVs for IS-IS Router CAPABILITY TLV
18.1. IGP IANA Considerations . . . . . . . . . . . . . . . . 39 Registry
18.1.1. IGP Algorithm Types Registry . . . . . . . . . . . . 39
18.1.2. IGP Metric-Type Registry . . . . . . . . . . . . . . 39
18.2. Flexible Algorithm Definition Flags Registry . . . . . . 40
18.3. IS-IS IANA Considerations . . . . . . . . . . . . . . . 40
18.3.1. IS-IS Sub-TLVs for IS-IS Router CAPABILITY TLV . . . 40
18.3.2. IS-IS Sub-TLVs for TLVs Advertising Prefix 18.3.2. IS-IS Sub-TLVs for TLVs Advertising Prefix
Reachability . . . . . . . . . . . . . . . . . . . . 41 Reachability Registry
18.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition 18.3.3. IS-IS Sub-Sub-TLVs for Flexible Algorithm Definition
Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . 41 Sub-TLV Registry
18.4. OSPF IANA Considerations . . . . . . . . . . . . . . . . 42 18.4. OSPF IANA Considerations
18.4.1. OSPF Router Information (RI) TLVs Registry . . . . . 42 18.4.1. OSPF Router Information (RI) TLVs Registry
18.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs . . . . . . . . 42 18.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs Registry
18.4.3. OSPFv3 Extended-LSA Sub-TLVs . . . . . . . . . . . . 42 18.4.3. OSPFv3 Extended-LSA Sub-TLVs Registry
18.4.4. OSPF Flex-Algorithm Prefix Metric Bits . . . . . . . 43 18.4.4. OSPF Flex-Algorithm Prefix Metric Bits Registry
18.4.5. OSPFv2 Opaque LSA Option Types . . . . . . . . . . . 43 18.4.5. Opaque Link-State Advertisements (LSA) Option Types
18.4.6. OSPFv2 Extended Inter-Area ASBR TLVs . . . . . . . . 44 Registry
18.4.7. OSPFv2 Inter-Area ASBR Sub-TLVs . . . . . . . . . . 44 18.4.6. OSPFv2 Extended Inter-Area ASBR TLVs Registry
18.4.8. OSPF Flexible Algorithm Definition TLV Sub-TLV 18.4.7. OSPFv2 Extended Inter-Area ASBR Sub-TLVs Registry
Registry . . . . . . . . . . . . . . . . . . . . . . 44 18.4.8. OSPF Flexible Algorithm Definition TLV Sub-TLVs
18.4.9. Link Attribute Applications Registry . . . . . . . . 46 Registry
19. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 46 18.4.9. Link Attribute Application Identifiers Registry
20. References . . . . . . . . . . . . . . . . . . . . . . . . . 46 19. References
20.1. Normative References . . . . . . . . . . . . . . . . . . 46 19.1. Normative References
20.2. Informative References . . . . . . . . . . . . . . . . . 48 19.2. Informative References
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 50 Acknowledgements
Authors' Addresses
1. Introduction 1. Introduction
An IGP-computed path based on the shortest IGP metric is often An IGP-computed path based on the shortest IGP metric is often
replaced by a traffic-engineered path due to requirements which are replaced by a traffic-engineered path due to requirements that are
not reflected by the IGP metric. Some networks engineer the IGP not reflected by the IGP metric. Some networks engineer the IGP
metric assignments in a way that the IGP metric reflects the link metric assignments in a way that the IGP metric reflects the link
bandwidth or delay. If, for example, the IGP metric reflects the bandwidth or delay. If, for example, the IGP metric reflects the
bandwidth on the link and user traffic is delay sensitive, the best bandwidth on the link and user traffic is delay sensitive, the best
IGP path may not reflect the best path from such a user's IGP path may not reflect the best path from such a user's
perspective. perspective.
To overcome this limitation, various sorts of traffic engineering To overcome this limitation, various sorts of Traffic Engineering
have been deployed, including RSVP-TE and SR-TE, in which case the TE have been deployed, including RSVP-TE and SR-TE, in which case the TE
component is responsible for computing paths based on additional component is responsible for computing paths based on additional
metrics and/or constraints. Such paths need to be installed in the metrics and/or constraints. Such paths need to be installed in the
forwarding tables in addition to, or as a replacement for, the forwarding tables in addition to, or as a replacement for, the
original paths computed by IGPs. Tunnels are often used to represent original paths computed by IGPs. Tunnels are often used to represent
the engineered paths and mechanisms like the one described in the engineered paths and mechanisms, like the one described in
[RFC3906] are used to replace the original IGP paths with such tunnel [RFC3906], and are used to replace the original IGP paths with such
paths. tunnel paths.
This document specifies a set of extensions to IS-IS, OSPFv2, and This document specifies a set of extensions to IS-IS, OSPFv2, and
OSPFv3 that enable a router to advertise TLVs that (a) identify OSPFv3 that enable a router to advertise TLVs that (a) identify a
calculation-type, (b) specify a metric-type, and (c) describe a set calculation-type, (b) specify a metric-type, and (c) describe a set
of constraints on the topology, that are to be used to compute the of constraints on the topology that are to be used to compute the
best paths along the constrained topology. A given combination of best paths along the constrained topology. A given combination of
calculation-type, metric-type, and constraints is known as a calculation-type, metric-type, and constraints is known as a
"Flexible Algorithm Definition". A router that sends such a set of "Flexible Algorithm Definition". A router that sends such a set of
TLVs also assigns a Flex-Algorithm value to the specified combination TLVs also assigns a Flex-Algorithm value to the specified combination
of calculation-type, metric-type, and constraints. of calculation-type, metric-type, and constraints.
This document also specifies a way for a router to use IGPs to This document also specifies a way for a router to use IGPs to
associate one or more "Segment Routing with the MPLS Data Plane (SR- associate one or more Segment Routing with the MPLS Data Plane (SR-
MPLS)" Prefix-SIDs [RFC8660], or "Segment Routing over IPv6 (SRv6)" MPLS) Prefix-SIDs [RFC8660] or Segment Routing over IPv6 (SRv6)
locators [RFC8986] with a particular Flex-Algorithm. Each such locators [RFC8986] with a particular Flex-Algorithm. Each such
Prefix-SID or SRv6 locator then represents a path that is computed Prefix-SID or SRv6 locator then represents a path that is computed
according to the identified Flex-Algorithm. In SRv6 it is the according to the identified Flex-Algorithm. In SRv6, it is the
locator, not the SID, that holds the binding to the algorithm. locator, not the Segment Identifier (SID), that holds the binding to
the algorithm.
2. Requirements Language 2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. Terminology 3. Terminology
This section defines terms that are often used in this document. This section defines terms that are often used in this document.
Flexible Algorithm Definition (FAD) - the set consisting of (a) Flexible Algorithm Definition (FAD): the set consisting of (a) a
calculation-type, (b) metric-type, and (c) a set of constraints. calculation-type, (b) a metric-type, and (c) a set of constraints.
Flex-Algorithm - a numeric identifier in the range 128-255 that is
associated via configuration with the Flexible Algorithm Definition.
Local Flexible Algorithm Definition - Flexible Algorithm Definition
defined locally on the node.
Remote Flexible Algorithm Definition - Flexible Algorithm Definition Flex-Algorithm: a numeric identifier in the range 128-255 that is
received from other nodes via IGP flooding. associated via configuration with the Flexible Algorithm
Definition.
Flexible Algorithm Participation - per data-plane configuration state Flexible Algorithm Participation: per the data plane configuration
that expresses whether the node is participating in a particular state that expresses whether the node is participating in a
Flexible Algorithm. Not all routers in a given network need to particular Flexible Algorithm. Not all routers in a given network
participate in a given Flexible Algorithm. The Flexible Algorithm(s) need to participate in a given Flexible Algorithm. The Flexible
a given router participates in is determined by configuration. Algorithm(s) that a given router participates in is determined by
configuration.
IGP Algorithm - value from the "IGP Algorithm Types" registry defined IGP Algorithm: value from the IANA "IGP Algorithm Types" registry
under "Interior Gateway Protocol (IGP) Parameters" IANA registry defined under the "Interior Gateway Protocol (IGP) Parameters"
grouping. IGP Algorithms represents the triplet (calculation-type, registry group. IGP Algorithms represent the triplet
metric-type, constraints), where the second and third elements of the (calculation-type, metric-type, and constraints), where the second
triple MAY be unspecified. and third elements of the triplet MAY be unspecified.
ABR - Area Border Router. In IS-IS terminology it is also known as ABR: Area Border Router. In IS-IS terminology, it is also known as
L1/L2 router. the Level 1 (L1) / Level 2 (L2) router.
ASBR - Autonomous System Border Router. ASBR: Autonomous System Border Router.
4. Flexible Algorithm 4. Flexible Algorithm
Many possible constraints may be used to compute a path over a Many possible constraints may be used to compute a path over a
network. Some networks are deployed as multiple planes. A simple network. Some networks are deployed as multiple planes. A simple
form of constraint may be to use a particular plane. A more form of constraint may be to use a particular plane. A more
sophisticated form of constraint can include some extended metric as sophisticated form of constraint can include some extended metric, as
described in [RFC8570]. Constraints which restrict paths to links described in [RFC8570]. Constraints that restrict paths to links
with specific affinities or avoid links with specific affinities are with specific affinities or avoid links with specific affinities are
also possible. Combinations of these are also possible. also possible. Combinations of these are also possible.
To provide maximum flexibility, a mechanism is provided that allows a To provide maximum flexibility, a mechanism is provided that allows a
router to (a) identify a particular calculation-type and (b) metric- router to identify a particular calculation-type and metric-type,
type, (c) describe a particular set of constraints, and (d) assign a describe a particular set of constraints, and assign a numeric
numeric identifier, referred to as Flex-Algorithm, to the combination identifier, referred to as Flex-Algorithm, to the combination of that
of that calculation-type, metric-type, and those constraints. The calculation-type, metric-type, and those constraints. The mapping
mapping between the Flex-Algorithm and its meaning is flexible and between the Flex-Algorithm and its meaning is flexible and defined by
defined by the user. As long as all routers in the domain have a the user. As long as all routers in the domain have a common
common understanding as to what a particular Flex-Algorithm understanding as to what a particular Flex-Algorithm represents, the
represents, the resulting routing computation is consistent and resulting routing computation is consistent and traffic is not
traffic is not subject to any looping. subject to any looping.
The set consisting of (a) calculation-type, (b) metric-type, and (c) The set consisting of (a) a calculation-type, (b) a metric-type, and
a set of constraints is referred to as a Flexible Algorithm (c) a set of constraints is referred to as a Flexible Algorithm
Definition. Definition.
Flex-Algorithm is a numeric identifier in the range 128-255 that is The Flex-Algorithm is a numeric identifier in the range 128-255 that
associated via configuration with the Flexible Algorithm Definition. is associated via configuration with the Flexible Algorithm
Definition.
The IANA "IGP Algorithm Types" registry defines the set of values for The IANA "IGP Algorithm Types" registry defines the set of values for
IGP Algorithms. The following values area allocated by IANA from IGP Algorithms. The following values are allocated by IANA from this
this registry for Flex-Algorithms: registry for Flex-Algorithms:
128-255 - Flex-Algorithms 128-255 - Flex-Algorithms
5. Flexible Algorithm Definition Advertisement 5. Flexible Algorithm Definition Advertisement
To guarantee loop-free forwarding for paths computed for a particular To guarantee loop-free forwarding for paths computed for a particular
Flex-Algorithm, all routers that (a) are configured to participate in Flex-Algorithm, all routers that (a) are configured to participate in
a particular Flex-Algorithm, and (b) are in the same Flex-Algorithm a particular Flex-Algorithm and (b) are in the same Flex-Algorithm
definition advertisement scope MUST agree on the definition of the Definition advertisement scope MUST agree on the definition of the
Flex-Algorithm. The following procedures ensure this condition is Flex-Algorithm. The following procedures ensure this condition is
fulfilled. fulfilled.
5.1. IS-IS Flexible Algorithm Definition Sub-TLV 5.1. IS-IS Flexible Algorithm Definition Sub-TLV
The IS-IS Flexible Algorithm Definition Sub-TLV (FAD Sub-TLV) is used The IS-IS Flexible Algorithm Definition (FAD) sub-TLV is used to
to advertise the definition of the Flex-Algorithm. advertise the definition of the Flex-Algorithm.
The IS-IS FAD Sub-TLV is advertised as a Sub-TLV of the IS-IS Router The IS-IS FAD sub-TLV is advertised as a sub-TLV of the IS-IS Router
Capability TLV-242 that is defined in [RFC7981]. CAPABILITY TLV-242, which is defined in [RFC7981].
IS-IS FAD Sub-TLV has the following format: The IS-IS FAD sub-TLV has the following format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |Flex-Algorithm | Metric-Type | | Type | Length |Flex-Algorithm | Metric-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Calc-Type | Priority | | Calc-Type | Priority |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs | | Sub-TLVs |
+ + + +
| ... | | ... |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where: where:
Type: 26
Type: 26 Length: variable number of octets, dependent on the included sub-
TLVs.
Length: variable number of octets, dependent on the included Sub-
TLVs
Flex-Algorithm: Flexible Algorithm number. Single octet value Flex-Algorithm: Flexible Algorithm number. Single octet value
between 128 and 255 inclusive. between 128 and 255 inclusive.
Metric-Type: Type of metric from the "IGP Metric-Type Registry" Metric-Type: type of metric from the IANA "IGP Metric-Type"
(Section 18.1.2) to be used during the calculation. The following registry (Section 18.1.2) to be used during the calculation.
values are defined: The following values are defined:
0: IGP Metric 0: IGP Metric
1: Min Unidirectional Link Delay as defined in [RFC8570], 1: Min Unidirectional Link Delay, as defined in Section 4.2 of
section 4.2, encoded as application specific link attribute as [RFC8570], encoded as an application-specific link
specified in [RFC8919] and Section 12 of this document. attribute, as specified in [RFC8919] and Section 12 of this
document.
2: Traffic Engineering Default Metric as defined in [RFC5305], 2: Traffic Engineering Default Metric, as defined in
section 3.7, encoded as application specific link attribute as Section 3.7 of [RFC5305], encoded as an application-specific
specified in [RFC8919] and Section 12 of this document. link attribute, as specified in [RFC8919] and Section 12 of
this document.
Calc-Type: calculation-type, value from 0 to 127 inclusive from Calc-Type: calculation-type. Value from 0-127 inclusive from the
the "IGP Algorithm Types" registry defined under "Interior Gateway IANA "IGP Algorithm Types" registry defined under the "Interior
Protocol (IGP) Parameters" IANA registries. IGP algorithms in the Gateway Protocol (IGP) Parameters" registry. IGP Algorithms in
range of 0-127 have a defined triplet (calculation-type, metric- the range of 0-127 have a defined triplet (calculation-type,
type, constraints). When used to specify the calculation-type in metric-type, constraints). When used to specify the
the FAD Sub-TLV, only the calculation-type defined for the calculation-type in the FAD sub-TLV, only the calculation-type
specified IGP Algorithm is used. The Metric/Constraints MUST NOT defined for the specified IGP Algorithm is used. The Metric/
be inherited. If the required calculation-type is Shortest Path Constraints MUST NOT be inherited. If the required
First, the value 0 MUST appear in this field. calculation-type is Shortest Path First, the value 0 MUST
appear in this field.
Priority: Value between 0 and 255 inclusive that specifies the Priority: value between 0 and 255 inclusive that specifies the
priority of the advertisement. Numerically greater values are priority of the advertisement. Numerically greater values are
preferred. Usage fo the priority is described in Section 5.3. preferred. Usage of the priority is described in Section 5.3.
Sub-TLVs - optional sub-TLVs. Sub-TLVs: optional sub-TLVs.
The IS-IS FAD Sub-TLV MAY be advertised in an LSP of any number. IS- The IS-IS FAD sub-TLV MAY be advertised in a Label Switched Path
IS router MAY advertise more than one IS-IS FAD Sub-TLV for a given (LSP) of any number. The IS-IS router MAY advertise more than one
Flexible Algorithm (see Section 6). IS-IS FAD sub-TLV for a given Flexible Algorithm (see Section 6).
The IS-IS FAD Sub-TLV has an area scope. The Router Capability TLV The IS-IS FAD sub-TLV has an area/level scope. The Router Capability
in which the FAD Sub-TLV is present MUST have the S-bit clear. TLV in which the FAD sub-TLV is present MUST have the S bit clear.
An IS-IS L1/L2 router MAY be configured to re-generate the winning An IS-IS L1/L2 router MAY be configured to regenerate the winning FAD
FAD from level 2, without any modification to it, to the level 1 from level 2, without any modification to it, to the level 1 area.
area. The re-generation of the FAD Sub-TLV from level 2 to level 1 The regeneration of the FAD sub-TLV from level 2 to level 1 is
is determined by the L1/L2 router, not by the originator of the FAD determined by the L1/L2 router, not by the originator of the FAD
advertisement in the level 2. In such a case, the re-generated FAD advertisement in level 2. In such a case, the regenerated FAD sub-
Sub-TLV will be advertised in the level 1 Router Capability TLV TLV will be advertised in the level 1 Router Capability TLV
originated by the L1/L2 router. originated by the L1/L2 router.
An L1/L2 router MUST NOT re-generate any FAD Sub-TLV from level 1 to An L1/L2 router MUST NOT regenerate any FAD sub-TLV from level 1 to
level 2. level 2.
5.2. OSPF Flexible Algorithm Definition TLV 5.2. OSPF Flexible Algorithm Definition TLV
The OSPF FAD TLV is advertised as a top-level TLV of the Router The OSPF FAD TLV is advertised as a top-level TLV of the Router
Information (RI) LSA that is defined in [RFC7770]. Information (RI) Link State Advertisement (LSA), which is defined in
[RFC7770].
The OSPF FAD TLV has the following format: The OSPF FAD TLV has the following format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Flex-Algorithm | Metric-Type | Calc-Type | Priority | |Flex-Algorithm | Metric-Type | Calc-Type | Priority |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs | | Sub-TLVs |
+ + + +
| ... | | ... |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where: where:
Type: 16
Type: 16 Length: variable number of octets, dependent on the included sub-
TLVs.
Length: variable number of octets, dependent on the included Sub-
TLVs
Flex-Algorithm: Flexible Algorithm number. Single octet value Flex-Algorithm: Flexible Algorithm number. Single octet value
between 128 and 255 inclusive. between 128 and 255 inclusive.
Metric-Type: Type of metric from the "IGP Metric-Type Registry" Metric-Type: type of metric from the IANA "IGP Metric-Type"
(Section 18.1.2) to be used during the calculation. The following registry (Section 18.1.2) to be used during the calculation.
values are defined: The following values are defined:
0: IGP Metric 0: IGP Metric
1: Min Unidirectional Link Delay as defined in [RFC7471], 1: Min Unidirectional Link Delay, as defined in Section 4.2 of
section 4.2, encoded as application specific link attribute as [RFC7471], encoded as an application-specific link
specified in [RFC8920] and Section 12 of this document. attribute, as specified in [RFC8920] and Section 12 of this
document.
2: Traffic Engineering metric as defined in [RFC3630], section 2: Traffic Engineering Metric, as defined in Section 2.5.5 of
2.5.5, encoded as application specific link attribute as [RFC3630], encoded as an application-specific link
specified in [RFC8920] and Section 12 of this document. attribute, as specified in [RFC8920] and Section 12 of this
document.
Calc-Type: as described in Section 5.1 Calc-Type: as described in Section 5.1.
Priority: as described in Section 5.1 Priority: as described in Section 5.1.
Sub-TLVs - optional sub-TLVs. Sub-TLVs: optional sub-TLVs.
When multiple OSPF FAD TLVs, for the same Flexible Algorithm, are When multiple OSPF FAD TLVs, for the same Flexible Algorithm, are
received from a given router, the receiver MUST use the first received from a given router, the receiver MUST use the first
occurrence of the TLV in the Router Information LSA. If the OSPF FAD occurrence of the TLV in the RI LSA. If the OSPF FAD TLV, for the
TLV, for the same Flex-Algorithm, appears in multiple Router same Flex-Algorithm, appears in multiple RI LSAs that have different
Information LSAs that have different flooding scopes, the OSPF FAD flooding scopes, the OSPF FAD TLV in the RI LSA with the area-scoped
TLV in the Router Information LSA with the area-scoped flooding scope flooding scope MUST be used. If the OSPF FAD TLV, for the same
MUST be used. If the OSPF FAD TLV, for the same algorithm, appears algorithm, appears in multiple RI LSAs that have the same flooding
in multiple Router Information LSAs that have the same flooding scope, the OSPF FAD TLV in the RI LSA with the numerically smallest
scope, the OSPF FAD TLV in the Router Information (RI) LSA with the Instance ID MUST be used and subsequent instances of the OSPF FAD TLV
numerically smallest Instance ID MUST be used and subsequent MUST be ignored.
instances of the OSPF FAD TLV MUST be ignored.
The RI LSA can be advertised at any of the defined opaque flooding The RI LSA can be advertised at any of the defined opaque flooding
scopes (link, area, or Autonomous System (AS)). For the purpose of scopes (link, area, or Autonomous System (AS)). For the purpose of
OSPF FAD TLV advertisement, area-scoped flooding is REQUIRED. The OSPF FAD TLV advertisement, area-scoped flooding is REQUIRED. The AS
Autonomous System flooding scope SHOULD NOT be used unless local flooding scope SHOULD NOT be used unless local configuration policy
configuration policy on the originating router indicates domain wide on the originating router indicates domain-wide flooding.
flooding.
5.3. Common Handling of Flexible Algorithm Definition TLV 5.3. Common Handling of the Flexible Algorithm Definition TLV
This section describes the protocol-independent handling of the FAD This section describes the protocol-independent handling of the FAD
TLV (OSPF) or FAD Sub-TLV (IS-IS). We will refer to it as FAD TLV in TLV (OSPF) or FAD sub-TLV (IS-IS). We will refer to it as FAD TLV in
this section, even though in the case of IS-IS it is a Sub-TLV. this section, even though, in the case of IS-IS, it is a sub-TLV.
The value of the Flex-Algorithm MUST be between 128 and 255 The value of the Flex-Algorithm MUST be between 128 and 255
inclusive. If it is not, the FAD TLV MUST be ignored. inclusive. If it is not, the FAD TLV MUST be ignored.
Only a subset of the routers participating in the particular Flex- Only a subset of the routers participating in the particular Flex-
Algorithm need to advertise the definition of the Flex-Algorithm. Algorithm need to advertise the definition of the Flex-Algorithm.
Every router, that is configured to participate in a particular Flex- Every router that is configured to participate in a particular Flex-
Algorithm, MUST select the Flex-Algorithm definition based on the Algorithm MUST select the Flex-Algorithm Definition based on the
following ordered rules. This allows for the consistent Flex- following ordered rules. This allows for the consistent Flex-
Algorithm definition selection in cases where different routers Algorithm Definition selection in cases where different routers
advertise different definitions for a given Flex-Algorithm: advertise different definitions for a given Flex-Algorithm:
1. From the advertisements of the FAD in the area (including both 1. From the advertisements of the FAD in the area (including both
locally generated advertisements and received advertisements) locally generated advertisements and received advertisements),
select the one(s) with the numerically greatest priority value. select the one(s) with the numerically greatest priority value.
2. If there are multiple advertisements of the FAD with the same 2. If there are multiple advertisements of the FAD with the same
numerically greatest priority, select the one that is originated numerically greatest priority, select the one that is originated
from the router with the numerically greatest System-ID, in the from the router with the numerically greatest System-ID, in the
case of IS-IS, or Router ID, in the case of OSPFv2 and OSPFv3. case of IS-IS, or Router ID, in the case of OSPFv2 and OSPFv3.
For IS-IS, the System-ID is described in [ISO10589]. For OSPFv2 For IS-IS, the System-ID is described in [ISO10589]. For OSPFv2
and OSPFv3, standard Router ID is described in [RFC2328] and and OSPFv3, the standard Router ID is described in [RFC2328] and
[RFC5340] respectively. [RFC5340], respectively.
The FAD selected according to these rules is also known as the The FAD selected according to these rules is also known as the
"winning FAD". "winning FAD".
A router that is not configured to participate in a particular Flex- A router that is not configured to participate in a particular Flex-
Algorithm MUST ignore FAD Sub-TLVs advertisements for such Flex- Algorithm MUST ignore FAD sub-TLV advertisements for such Flex-
Algorithm. Algorithm.
A router that is not participating in a particular Flex-Algorithm MAY A router that is not participating in a particular Flex-Algorithm MAY
advertise FAD for such Flex-Algorithm. Receiving routers MUST advertise the FAD for such Flex-Algorithm. Receiving routers MUST
consider a received FAD advertisement regardless of the Flex- consider a received FAD advertisement regardless of the Flex-
Algorithm participation of that FAD advertisement's originator. Algorithm participation of that FAD advertisement's originator.
Any change in the Flex-Algorithm definition may result in temporary Any change in the Flex-Algorithm Definition may result in a temporary
disruption of traffic that is forwarded based on such Flex-Algorithm disruption of traffic that is forwarded based on such Flex-Algorithm
paths. The impact is similar to any other event that requires paths. The impact is similar to any other event that requires
network-wide convergence. network-wide convergence.
If a node is configured to participate in a particular Flexible If a node is configured to participate in a particular Flexible
Algorithm, but there is no valid Flex-Algorithm definition available Algorithm, but there is no valid Flex-Algorithm Definition available
for it, or the selected Flex-Algorithm definition includes for it or the selected Flex-Algorithm Definition includes
calculation-type, metric-type, constraint, flag, or Sub-TLV that is calculation-type, metric-type, constraint, flag, or sub-TLV that is
not supported by the node, it MUST stop participating in such not supported by the node, it MUST stop participating in such
Flexible Algorithm. That implies that it MUST NOT announce Flexible Algorithm. That implies that it MUST NOT announce
participation for such Flexible Algorithm as specified in Section 11 participation for such Flexible Algorithm, as specified in
and it MUST remove any forwarding state associated with it. Section 11, and it MUST remove any forwarding state associated with
it.
Flex-Algorithm definition is topology independent. It applies to all The Flex-Algorithm Definition is topology independent. It applies to
topologies that a router participates in. all topologies that a router participates in.
6. Sub-TLVs of IS-IS FAD Sub-TLV 6. Sub-TLVs of IS-IS FAD Sub-TLV
One of the limitations of IS-IS [ISO10589] is that the length of a One of the limitations of IS-IS [ISO10589] is that the length of a
TLV/sub-TLV is limited to a maximum of 255 octets. For the FAD sub- TLV/sub-TLV is limited to a maximum of 255 octets. For the FAD sub-
TLV, there are a number of sub-sub-TLVs (defined below) which are TLV, there are a number of sub-sub-TLVs (defined below) that are
supported. For a given Flex-Algorithm, it is possible that the total supported. For a given Flex-Algorithm, it is possible that the total
number of octets required to completely define a FAD exceeds the number of octets required to completely define a FAD exceeds the
maximum length supported by a single FAD sub-TLV. In such cases, the maximum length supported by a single FAD sub-TLV. In such cases, the
FAD MAY be split into multiple such sub-TLVs and the content of the FAD MAY be split into multiple such sub-TLVs, and the content of the
multiple FAD sub-TLVs combined to provide a complete FAD for the multiple FAD sub-TLVs are combined to provide a complete FAD for the
Flex-Algorithm. In such a case, the fixed portion of the FAD (see Flex-Algorithm. In such a case, the fixed portion of the FAD (see
Section 5.1) MUST be identical in all FAD sub-TLVs for a given Flex- Section 5.1) MUST be identical in all FAD sub-TLVs for a given Flex-
Algorithm from a given IS. In case the fixed portion of such FAD Algorithm from a given IS. In case the fixed portion of such FAD
Sub-TLVs differ, the values in the fixed portion in the FAD sub-TLV sub-TLVs differ, the values in the fixed portion in the FAD sub-TLV
in the first occurrence in the lowest numbered LSP from a given IS in the first occurrence in the lowest-numbered LSP from a given IS
MUST be used. MUST be used.
Any specification that introduces a new IS-IS FAD sub-sub-TLV MUST Any specification that introduces a new IS-IS FAD sub-sub-TLV MUST
specify whether the FAD sub-TLV may appear multiple times in the set specify whether the FAD sub-TLV may appear multiple times in the set
of FAD sub-TLVs for a given Flex-Algorithm from a given IS and how to of FAD sub-TLVs for a given Flex-Algorithm from a given IS and how to
handle them if multiple are allowed. handle them if multiple are allowed.
6.1. IS-IS Flexible Algorithm Exclude Admin Group Sub-TLV 6.1. IS-IS Flexible Algorithm Exclude Admin Group Sub-TLV
The Flexible Algorithm definition can specify 'colors' that are used The Flexible Algorithm Definition can specify "colors" that are used
by the operator to exclude links during the Flex-Algorithm path by the operator to exclude links during the Flex-Algorithm path
computation. computation.
The IS-IS Flexible Algorithm Exclude Admin Group Sub-TLV is used to The IS-IS Flexible Algorithm Exclude Admin Group (FAEAG) sub-TLV is
advertise the exclude rule that is used during the Flex-Algorithm used to advertise the exclude rule that is used during the Flex-
path calculation as specified in Section 13. Algorithm path calculation, as specified in Section 13.
The IS-IS Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub- The IS-IS FAEAG sub-TLV is a sub-TLV of the IS-IS FAD sub-TLV. It
TLV) is a Sub-TLV of the IS-IS FAD Sub-TLV. It has the following has the following format:
format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Admin Group | | Extended Admin Group |
+- -+ +- -+
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: 1 where:
Type: 1
Length: variable, dependent on the size of the Extended Admin Length: variable, dependent on the size of the Extended Admin
Group. MUST be a multiple of 4 octets. Group. MUST be a multiple of 4 octets.
Extended Administrative Group: Extended Administrative Group as Extended Administrative Group: Extended Administrative Group, as
defined in [RFC7308]. defined in [RFC7308].
The IS-IS FAEAG Sub-TLV MUST NOT appear more than once in a single The IS-IS FAEAG sub-TLV MUST NOT appear more than once in a single
IS-IS FAD Sub-TLV. If it appears more than once, the IS-IS FAD Sub- IS-IS FAD sub-TLV. If it appears more than once, the IS-IS FAD sub-
TLV MUST be ignored by the receiver. TLV MUST be ignored by the receiver.
The IS-IS FAEAG Sub-TLV MUST NOT appear more than once in the set of The IS-IS FAEAG sub-TLV MUST NOT appear more than once in the set of
FAD sub-TLVs for a given Flex-Algorithm from a given IS. If it FAD sub-TLVs for a given Flex-Algorithm from a given IS. If it
appears more than once in such a set, the IS-IS FAEAG Sub-TLV in the appears more than once in such a set, the IS-IS FAEAG sub-TLV in the
first occurrence in the lowest numbered LSP from a given IS MUST be first occurrence in the lowest-numbered LSP from a given IS MUST be
used and any other occurrences MUST be ignored. used, and any other occurrences MUST be ignored.
6.2. IS-IS Flexible Algorithm Include-Any Admin Group Sub-TLV 6.2. IS-IS Flexible Algorithm Include-Any Admin Group Sub-TLV
The Flexible Algorithm definition can specify 'colors' that are used The Flexible Algorithm Definition can specify "colors" that are used
by the operator to include links during the Flex-Algorithm path by the operator to include links during the Flex-Algorithm path
computation. computation.
The IS-IS Flexible Algorithm Include-Any Admin Group Sub-TLV is used The IS-IS Flexible Algorithm Include-Any Admin Group sub-TLV is used
to advertise the include-any rule that is used during the Flex- to advertise the include-any rule that is used during the Flex-
Algorithm path calculation as specified in Section 13. Algorithm path calculation, as specified in Section 13.
The IS-IS Flexible Algorithm Include-Any Admin Group Sub-TLV is a The IS-IS Flexible Algorithm Include-Any Admin Group sub-TLV is a
Sub-TLV of the IS-IS FAD Sub-TLV. It has the following format: sub-TLV of the IS-IS FAD sub-TLV. It has the following format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Admin Group | | Extended Admin Group |
+- -+ +- -+
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: 2 where:
Type: 2
Length: variable, dependent on the size of the Extended Admin Length: variable, dependent on the size of the Extended Admin
Group. MUST be a multiple of 4 octets. Group. MUST be a multiple of 4 octets.
Extended Administrative Group: Extended Administrative Group as Extended Administrative Group: Extended Administrative Group, as
defined in [RFC7308]. defined in [RFC7308].
The IS-IS Flexible Algorithm Include-Any Admin Group Sub-TLV MUST NOT The IS-IS Flexible Algorithm Include-Any Admin Group sub-TLV MUST NOT
appear more than once in a single IS-IS FAD Sub-TLV. If it appears appear more than once in a single IS-IS FAD sub-TLV. If it appears
more than once, the IS-IS FAD Sub-TLV MUST be ignored by the more than once, the IS-IS FAD sub-TLV MUST be ignored by the
receiver. receiver.
The IS-IS Flexible Algorithm Include-Any Admin Group Sub-TLV MUST NOT The IS-IS Flexible Algorithm Include-Any Admin Group sub-TLV MUST NOT
appear more than once in the set of FAD sub-TLVs for a given Flex- appear more than once in the set of FAD sub-TLVs for a given Flex-
Algorithm from a given IS. If it appears more than once in such a Algorithm from a given IS. If it appears more than once in such a
set, the IS-IS Flexible Algorithm Include-Any Admin Group Sub-TLV in set, the IS-IS Flexible Algorithm Include-Any Admin Group sub-TLV in
the first occurrence in the lowest numbered LSP from a given IS MUST the first occurrence in the lowest-numbered LSP from a given IS MUST
be used and any other occurrences MUST be ignored. be used, and any other occurrences MUST be ignored.
6.3. IS-IS Flexible Algorithm Include-All Admin Group Sub-TLV 6.3. IS-IS Flexible Algorithm Include-All Admin Group Sub-TLV
The Flexible Algorithm definition can specify 'colors' that are used The Flexible Algorithm Definition can specify "colors" that are used
by the operator to include links during the Flex-Algorithm path by the operator to include links during the Flex-Algorithm path
computation. computation.
The IS-IS Flexible Algorithm Include-All Admin Group Sub-TLV is used The IS-IS Flexible Algorithm Include-All Admin Group sub-TLV is used
to advertise the include-all rule that is used during the Flex- to advertise the include-all rule that is used during the Flex-
Algorithm path calculation as specified in Section 13. Algorithm path calculation, as specified in Section 13.
The IS-IS Flexible Algorithm Include-All Admin Group Sub-TLV is is a The IS-IS Flexible Algorithm Include-All Admin Group sub-TLV is a
Sub-TLV of the IS-IS FAD Sub-TLV. It has the following format: sub-TLV of the IS-IS FAD sub-TLV. It has the following format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Admin Group | | Extended Admin Group |
+- -+ +- -+
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: 3 where:
Type: 3
Length: variable, dependent on the size of the Extended Admin Length: variable, dependent on the size of the Extended Admin
Group. MUST be a multiple of 4 octets. Group. MUST be a multiple of 4 octets.
Extended Administrative Group: Extended Administrative Group as Extended Administrative Group: Extended Administrative Group, as
defined in [RFC7308]. defined in [RFC7308].
The IS-IS Flexible Algorithm Include-All Admin Group Sub-TLV MUST NOT The IS-IS Flexible Algorithm Include-All Admin Group sub-TLV MUST NOT
appear more than once in a single IS-IS FAD Sub-TLV. If it appears appear more than once in a single IS-IS FAD sub-TLV. If it appears
more than once, the IS-IS FAD Sub-TLV MUST be ignored by the more than once, the IS-IS FAD sub-TLV MUST be ignored by the
receiver. receiver.
The IS-IS Flexible Algorithm Include-All Admin Group Sub-TLV MUST NOT The IS-IS Flexible Algorithm Include-All Admin Group sub-TLV MUST NOT
appear more than once in the set of FAD sub-TLVs for a given Flex- appear more than once in the set of FAD sub-TLVs for a given Flex-
Algorithm from a given IS. If it appears more than once in such a Algorithm from a given IS. If it appears more than once in such a
set, the IS-IS Flexible Algorithm Include-All Admin Group Sub-TLV in set, the IS-IS Flexible Algorithm Include-All Admin Group sub-TLV in
the first occurrence in the lowest numbered LSP from a given IS MUST the first occurrence in the lowest-numbered LSP from a given IS MUST
be used and any other occurrences MUST be ignored. be used, and any other occurrences MUST be ignored.
6.4. IS-IS Flexible Algorithm Definition Flags Sub-TLV 6.4. IS-IS Flexible Algorithm Definition Flags Sub-TLV
The IS-IS Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) The IS-IS Flexible Algorithm Definition Flags (FADF) sub-TLV is a
is a Sub-TLV of the IS-IS FAD Sub-TLV. It has the following format: sub-TLV of the IS-IS FAD sub-TLV. It has the following format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | | Flags |
+- -+ +- -+
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: 4 where:
Type: 4
Length: variable, number of octets of the Flags field Length: variable, number of octets of the Flags field.
Flags: Flags:
0 1 2 3 4 5 6 7...
+-+-+-+-+-+-+-+-+...
|M| | | ...
+-+-+-+-+-+-+-+-+...
0 1 2 3 4 5 6 7... M-flag: when set, the Flex-Algorithm-specific prefix metric
+-+-+-+-+-+-+-+-+... MUST be used for inter-area and external prefix calculation.
|M| | | ... This flag is not applicable to prefixes advertised as SRv6
+-+-+-+-+-+-+-+-+... locators.
M-flag: when set, the Flex-Algorithm specific prefix metric
MUST be used for inter-area and external prefix calculation.
This flag is not applicable to prefixes advertised as SRv6
locators.
A new IANA "IGP Flexible Algorithm Definition Flags Registry" is A new IANA "IGP Flexible Algorithm Definition Flags" registry is
defined for allocation of bits in the Flags field - see Section 18.2. defined for allocation of bits in the Flags field -- see
Section 18.2.
Bits are defined/sent starting with Bit 0 defined above. Additional Bits are defined/sent starting with bit 0 defined above. Additional
bit definitions that may be defined in the future SHOULD be assigned bit definitions that may be defined in the future SHOULD be assigned
in ascending bit order so as to minimize the number of bits that will in ascending bit order to minimize the number of bits that will need
need to be transmitted. to be transmitted.
Undefined bits MUST be transmitted as 0. Undefined bits MUST be transmitted as 0.
Bits that are not transmitted MUST be treated as if they are set to 0 Bits that are not transmitted MUST be treated as if they are set to 0
on receipt. on receipt.
The IS-IS FADF Sub-TLV MUST NOT appear more than once in a single IS- The IS-IS FADF sub-TLV MUST NOT appear more than once in a single IS-
IS FAD Sub-TLV. If it appears more than once, the IS-IS FAD Sub-TLV IS FAD sub-TLV. If it appears more than once, the IS-IS FAD sub-TLV
MUST be ignored by the receiver. MUST be ignored by the receiver.
The IS-IS FADF Sub-TLV MUST NOT appear more than once in the set of The IS-IS FADF sub-TLV MUST NOT appear more than once in the set of
FAD sub-TLVs for a given Flex-Algorithm from a given IS. If it FAD sub-TLVs for a given Flex-Algorithm from a given IS. If it
appears more than once in such a set, the IS-IS FADF Sub-TLV in the appears more than once in such a set, the IS-IS FADF sub-TLV in the
first occurrence in the lowest numbered LSP from a given IS MUST be first occurrence in the lowest-numbered LSP from a given IS MUST be
used and any other occurrences MUST be ignored. used, and any other occurrences MUST be ignored.
If the IS-IS FADF Sub-TLV is not present inside the IS-IS FAD Sub- If the IS-IS FADF sub-TLV is not present inside the IS-IS FAD sub-
TLV, all the bits are assumed to be set to 0. TLV, all the bits are assumed to be set to 0.
If a node is configured to participate in a particular Flexible If a node is configured to participate in a particular Flexible
Algorithm, but the selected Flex-Algorithm definition includes a bit Algorithm, but the selected Flex-Algorithm Definition includes a bit
in the IS-IS FADF Sub-TLV that is not supported by the node, it MUST in the IS-IS FADF sub-TLV that is not supported by the node, it MUST
stop participating in such Flexible Algorithm. stop participating in such Flexible Algorithm.
New flag bits may be defined in the future. Implementations MUST New flag bits may be defined in the future. Implementations MUST
check all advertised flag bits in the received IS-IS FADF Sub-TLV - check all advertised flag bits in the received IS-IS FADF sub-TLV --
not just the subset currently defined. not just the subset currently defined.
M-flag MUST not be used when calculating prefix reachability for SRv6 The M-flag MUST not be used when calculating prefix reachability for
Locator prefix. the SRv6 Locator prefix.
6.5. IS-IS Flexible Algorithm Exclude SRLG Sub-TLV 6.5. IS-IS Flexible Algorithm Exclude SRLG Sub-TLV
The Flexible Algorithm definition can specify Shared Risk Link Groups The Flexible Algorithm Definition can specify Shared Risk Link Groups
(SRLGs) that the operator wants to exclude during the Flex-Algorithm (SRLGs) that the operator wants to exclude during the Flex-Algorithm
path computation. path computation.
The IS-IS Flexible Algorithm Exclude SRLG Sub-TLV (FAESRLG) is used The IS-IS Flexible Algorithm Exclude SRLG (FAESRLG) sub-TLV is used
to advertise the exclude rule that is used during the Flex-Algorithm to advertise the exclude rule that is used during the Flex-Algorithm
path calculation as specified in Section 13. path calculation, as specified in Section 13.
The IS-IS FAESRLG Sub-TLV is a Sub-TLV of the IS-IS FAD Sub-TLV. It The IS-IS FAESRLG sub-TLV is a sub-TLV of the IS-IS FAD sub-TLV. It
has the following format: has the following format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Shared Risk Link Group Value | | Shared Risk Link Group Value |
+- -+ +- -+
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: 5 where:
Type: 5
Length: variable, dependent on number of SRLG values. MUST be a Length: variable, dependent on number of SRLG values. MUST be a
multiple of 4 octets. multiple of 4 octets.
Shared Risk Link Group Value: SRLG value as defined in [RFC5307]. Shared Risk Link Group Value: SRLG value, as defined in
[RFC5307].
The IS-IS FAESRLG Sub-TLV MUST NOT appear more than once in a single The IS-IS FAESRLG sub-TLV MUST NOT appear more than once in a single
IS-IS FAD Sub-TLV. If it appears more than once, the IS-IS FAD Sub- IS-IS FAD sub-TLV. If it appears more than once, the IS-IS FAD sub-
TLV MUST be ignored by the receiver. TLV MUST be ignored by the receiver.
The IS-IS FAESRLG Sub-TLV MAY appear more than once in the set of FAD The IS-IS FAESRLG sub-TLV MAY appear more than once in the set of FAD
sub-TLVs for a given Flex-Algorithm from a given IS. This may be sub-TLVs for a given Flex-Algorithm from a given IS. This may be
necessary in cases where the total number of SRLG values which are necessary in cases where the total number of SRLG values that are
specified cause the FAD sub-TLV to exceed the maximum length of a specified cause the FAD sub-TLV to exceed the maximum length of a
single FAD sub-TLV. In such a case the receiver MUST use the union single FAD sub-TLV. In such a case, the receiver MUST use the union
of all values across all IS-IS FAESRLG Sub-TLVs from such set. of all values across all IS-IS FAESRLG sub-TLVs from such set.
7. Sub-TLVs of OSPF FAD TLV 7. Sub-TLVs of the OSPF FAD TLV
7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV 7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV
The Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub-TLV) is The OSPF Flexible Algorithm Exclude Admin Group (FAEAG) sub-TLV is a
a Sub-TLV of the OSPF FAD TLV. Its usage is described in sub-TLV of the OSPF FAD TLV. Its usage is described in Section 6.1.
Section 6.1. It has the following format: It has the following format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Admin Group | | Extended Admin Group |
+- -+ +- -+
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: 1 where:
Type: 1
Length: variable, dependent on the size of the Extended Admin Length: variable, dependent on the size of the Extended Admin
Group. MUST be a multiple of 4 octets. Group. MUST be a multiple of 4 octets.
Extended Administrative Group: Extended Administrative Group as Extended Administrative Group: Extended Administrative Group, as
defined in [RFC7308]. defined in [RFC7308].
The OSPF FAEAG Sub-TLV MUST NOT appear more than once in an OSPF FAD The OSPF FAEAG sub-TLV MUST NOT appear more than once in an OSPF FAD
TLV. If it appears more than once, the OSPF FAD TLV MUST be ignored TLV. If it appears more than once, the OSPF FAD TLV MUST be ignored
by the receiver. by the receiver.
7.2. OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV 7.2. OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV
The OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV is a Sub- The OSPF Flexible Algorithm Include-Any Admin Group sub-TLV is a sub-
TLV of the OSPF FAD TLV. The usage of this Sub-TLVs is described in TLV of the OSPF FAD TLV. The usage of this sub-TLV is described in
Section 6.2. It has the following format: Section 6.2. It has the following format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Admin Group | | Extended Admin Group |
+- -+ +- -+
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: 2 where:
Type: 2
Length: variable, dependent on the size of the Extended Admin Length: variable, dependent on the size of the Extended Admin
Group. MUST be a multiple of 4 octets. Group. MUST be a multiple of 4 octets.
Extended Administrative Group: Extended Administrative Group as Extended Administrative Group: Extended Administrative Group, as
defined in [RFC7308]. defined in [RFC7308].
The OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV MUST NOT The OSPF Flexible Algorithm Include-Any Admin Group sub-TLV MUST NOT
appear more than once in an OSPF FAD TLV. If it appears more than appear more than once in an OSPF FAD TLV. If it appears more than
once, the OSPF FAD TLV MUST be ignored by the receiver. once, the OSPF FAD TLV MUST be ignored by the receiver.
7.3. OSPF Flexible Algorithm Include-All Admin Group Sub-TLV 7.3. OSPF Flexible Algorithm Include-All Admin Group Sub-TLV
The OSPF Flexible Algorithm Include-All Admin Group Sub-TLV is a Sub- The OSPF Flexible Algorithm Include-All Admin Group sub-TLV is a sub-
TLV of the OSPF FAD TLV. The usage of this Sub-TLVs is described in TLV of the OSPF FAD TLV. The usage of this sub-TLV is described in
Section 6.3. It has the following format: Section 6.3. It has the following format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Admin Group | | Extended Admin Group |
+- -+ +- -+
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: 3 where:
Type: 3
Length: variable, dependent on the size of the Extended Admin Length: variable, dependent on the size of the Extended Admin
Group. MUST be a multiple of 4 octets. Group. MUST be a multiple of 4 octets.
Extended Administrative Group: Extended Administrative Group as Extended Administrative Group: Extended Administrative Group, as
defined in [RFC7308]. defined in [RFC7308].
The OSPF Flexible Algorithm Include-All Admin Group Sub-TLV MUST NOT The OSPF Flexible Algorithm Include-All Admin Group sub-TLV MUST NOT
appear more than once in an OSPF FAD TLV. If it appears more than appear more than once in an OSPF FAD TLV. If it appears more than
once, the OSPF FAD TLV MUST be ignored by the receiver. once, the OSPF FAD TLV MUST be ignored by the receiver.
7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV 7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV
The OSPF Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) The OSPF Flexible Algorithm Definition Flags (FADF) sub-TLV is a sub-
is a Sub-TLV of the OSPF FAD TLV. It has the following format: TLV of the OSPF FAD TLV. It has the following format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | | Flags |
+- -+ +- -+
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: 4 where:
Type: 4
Length: variable, dependent on the size of the Flags field. MUST Length: variable, dependent on the size of the Flags field. MUST
be a multiple of 4 octets. be a multiple of 4 octets.
Flags: Flags:
0 1 2 3 4 5 6 7...
+-+-+-+-+-+-+-+-+...
|M| | | ...
+-+-+-+-+-+-+-+-+...
0 1 2 3 4 5 6 7... M-flag: when set, the Flex-Algorithm-specific prefix and ASBR
+-+-+-+-+-+-+-+-+... metric MUST be used for inter-area and external prefix
|M| | | ... calculation. This flag is not applicable to prefixes
+-+-+-+-+-+-+-+-+... advertised as SRv6 locators.
M-flag: when set, the Flex-Algorithm specific prefix and ASBR
metric MUST be used for inter-area and external prefix
calculation. This flag is not applicable to prefixes
advertised as SRv6 locators.
A new IANA "IGP Flexible Algorithm Definition Flags Registry" is A new IANA "IGP Flexible Algorithm Definition Flags" registry is
defined for allocation of bits in the Flags field - see Section 18.2. defined for allocation of bits in the Flags field -- see
Section 18.2.
Bits are defined/sent starting with Bit 0 defined above. Additional Bits are defined/sent starting with bit 0 defined above. Additional
bit definitions that may be defined in the future SHOULD be assigned bit definitions that may be defined in the future SHOULD be assigned
in ascending bit order so as to minimize the number of bits that will in ascending bit order to minimize the number of bits that will need
need to be transmitted. to be transmitted.
Undefined bits MUST be transmitted as 0. Undefined bits MUST be transmitted as 0.
Bits that are not transmitted MUST be treated as if they are set to 0 Bits that are not transmitted MUST be treated as if they are set to 0
on receipt. on receipt.
The OSPF FADF Sub-TLV MUST NOT appear more than once in an OSPF FAD The OSPF FADF sub-TLV MUST NOT appear more than once in an OSPF FAD
TLV. If it appears more than once, the OSPF FAD TLV MUST be ignored TLV. If it appears more than once, the OSPF FAD TLV MUST be ignored
by the receiver. by the receiver.
If the OSPF FADF Sub-TLV is not present inside the OSPF FAD TLV, all If the OSPF FADF sub-TLV is not present inside the OSPF FAD TLV, all
the bits are assumed to be set to 0. the bits are assumed to be set to 0.
If a node is configured to participate in a particular Flexible If a node is configured to participate in a particular Flexible
Algorithm, but the selected Flex-Algorithm definition includes a bit Algorithm, but the selected Flex-Algorithm Definition includes a bit
in the OSPF FADF Sub-TLV that is not supported by the node, it MUST in the OSPF FADF sub-TLV that is not supported by the node, it MUST
stop participating in such Flexible Algorithm. stop participating in such Flexible Algorithm.
New flag bits may be defined in the future. Implementations MUST New flag bits may be defined in the future. Implementations MUST
check all advertised flag bits in the received OSPF FADF Sub-TLV - check all advertised flag bits in the received OSPF FADF sub-TLV --
not just the subset currently defined. not just the subset currently defined.
M-flag MUST not be used when calculating prefix reachability for SRv6 The M-flag MUST not be used when calculating prefix reachability for
Locator prefix. the SRv6 Locator prefix.
7.5. OSPF Flexible Algorithm Exclude SRLG Sub-TLV 7.5. OSPF Flexible Algorithm Exclude SRLG Sub-TLV
The OSPF Flexible Algorithm Exclude SRLG Sub-TLV (FAESRLG Sub-TLV) is The OSPF Flexible Algorithm Exclude SRLG (FAESRLG) sub-TLV is a sub-
a Sub-TLV of the OSPF FAD TLV. Its usage is described in TLV of the OSPF FAD TLV. Its usage is described in Section 6.5. It
Section 6.5. It has the following format: has the following format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Shared Risk Link Group Value | | Shared Risk Link Group Value |
+- -+ +- -+
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: 5 where:
Type: 5
Length: variable, dependent on the number of SRLGs. MUST be a Length: variable, dependent on the number of SRLGs. MUST be a
multiple of 4 octets. multiple of 4 octets.
Shared Risk Link Group Value: SRLG value as defined in [RFC4203]. Shared Risk Link Group Value: SRLG value, as defined in
[RFC4203].
The OSPF FAESRLG Sub-TLV MUST NOT appear more than once in an OSPF The OSPF FAESRLG sub-TLV MUST NOT appear more than once in an OSPF
FAD TLV. If it appears more than once, the OSPF FAD TLV MUST be FAD TLV. If it appears more than once, the OSPF FAD TLV MUST be
ignored by the receiver. ignored by the receiver.
8. IS-IS Flexible Algorithm Prefix Metric Sub-TLV 8. IS-IS Flexible Algorithm Prefix Metric Sub-TLV
The IS-IS Flexible Algorithm Prefix Metric (FAPM) Sub-TLV supports The IS-IS Flexible Algorithm Prefix Metric (FAPM) sub-TLV supports
the advertisement of a Flex-Algorithm specific prefix metric the advertisement of a Flex-Algorithm-specific prefix metric
associated with a given prefix advertisement. associated with a given prefix advertisement.
The IS-IS FAPM Sub-TLV is a sub-TLV of TLVs 135, 235, 236, and 237 The IS-IS FAPM sub-TLV is a sub-TLV of TLVs 135, 235, 236, and 237
and has the following format: and has the following format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |Flex-Algorithm | | Type | Length |Flex-Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric | | Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: 6 where:
Type: 6
Length: 5 octets Length: 5 octets
Flex-Algorithm: Single octet value between 128 and 255 inclusive. Flex-Algorithm: single octet value between 128 and 255 inclusive.
Metric: 4 octets of metric information Metric: 4 octets of metric information.
The IS-IS FAPM Sub-TLV MAY appear multiple times in its parent TLV. The IS-IS FAPM sub-TLV MAY appear multiple times in its parent TLV.
If it appears more than once with the same Flex-Algorithm value, the If it appears more than once with the same Flex-Algorithm value, the
first instance MUST be used and any subsequent instances MUST be first instance MUST be used and any subsequent instances MUST be
ignored. ignored.
If a prefix is advertised with a Flex-Algorithm prefix metric larger If a prefix is advertised with a Flex-Algorithm prefix metric larger
than MAX_PATH_METRIC as defined in [RFC5305] this prefix MUST NOT be than MAX_PATH_METRIC, as defined in [RFC5305], this prefix MUST NOT
considered during the Flexible Algorithm computation. be considered during the Flexible Algorithm computation.
The usage of the Flex-Algorithm prefix metric is described in The usage of the Flex-Algorithm prefix metric is described in
Section 13. Section 13.
The IS-IS FAPM Sub-TLV MUST NOT be advertised as a sub-TLV of the IS- The IS-IS FAPM sub-TLV MUST NOT be advertised as a sub-TLV of the IS-
IS SRv6 Locator TLV [I-D.ietf-lsr-isis-srv6-extensions]. The IS-IS IS SRv6 Locator TLV [RFC9352]. The IS-IS SRv6 Locator TLV includes
SRv6 Locator TLV includes the Algorithm and Metric fields which MUST the Algorithm and Metric fields, which MUST be used instead. If the
be used instead. If the FAPM Sub-TLV is present as a sub-TLV of the FAPM sub-TLV is present as a sub-TLV of the IS-IS SRv6 Locator TLV in
IS-IS SRv6 Locator TLV in the received LSP, such FAPM Sub-TLV MUST be the received LSP, such FAPM sub-TLV MUST be ignored.
ignored.
9. OSPF Flexible Algorithm Prefix Metric Sub-TLV 9. OSPF Flexible Algorithm Prefix Metric Sub-TLV
The OSPF Flexible Algorithm Prefix Metric (FAPM) Sub-TLV supports the The OSPF Flexible Algorithm Prefix Metric (FAPM) sub-TLV supports the
advertisement of a Flex-Algorithm specific prefix metric associated advertisement of a Flex-Algorithm-specific prefix metric associated
with a given prefix advertisement. with a given prefix advertisement.
The OSPF Flex-Algorithm Prefix Metric (FAPM) Sub-TLV is a Sub-TLV of The OSPF FAPM sub-TLV is a sub-TLV of the:
the:
- OSPFv2 Extended Prefix TLV [RFC7684] * OSPFv2 Extended Prefix TLV [RFC7684] and
- Following OSPFv3 TLVs as defined in [RFC8362]: * following OSPFv3 TLVs, as defined in [RFC8362]:
Inter-Area Prefix TLV - Inter-Area Prefix TLV
External Prefix TLV - External-Prefix TLV
OSPF FAPM Sub-TLV has the following format: The OSPF FAPM sub-TLV has the following format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Flex-Algorithm | Flags | Reserved | |Flex-Algorithm | Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric | | Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where: where:
Type: 3 for OSPFv2, and 26 for OSPFv3
Type: 3 for OSPFv2, 26 for OSPFv3 Length: 8 octets
Length: 8 octets Flex-Algorithm: single octet value between 128 and 255 inclusive.
Flex-Algorithm: Single octet value between 128 and 255 inclusive. Flags: 1-octet value
Flags: One octet value 0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+ |E| |
|E| | +-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+
E bit : position 0: The type of external metric. If bit is E bit: position 0: The type of external metric. If the bit is
set, the metric specified is a Type 2 external metric. This set, the metric specified is a Type 2 external metric. This
bit is applicable only to OSPF External and NSSA external bit is applicable only to OSPF external and Not-So-Stubby
prefixes. This is semantically the same as the E bit in Area (NSSA) external prefixes. This is semantically the
section A.4.5 of [RFC2328] and section A.4.7 of [RFC5340] for same as the E bit in Appendix A.4.5 of [RFC2328] and
OSPFv2 and OSPFv3 respectively. Appendix A.4.7 of [RFC5340] for OSPFv2 and OSPFv3,
respectively.
Bits 1 through 7: MUST be cleared by originator and ignored by Bits 1 through 7: MUST be cleared by the originator and
receiver. ignored by the receiver.
Reserved: MUST be set to 0, ignored at reception. Reserved: MUST be set to 0 and ignored at reception.
Metric: 4 octets of metric information Metric: 4 octets of metric information.
The OSPF FAPM Sub-TLV MAY appear multiple times in its parent TLV. The OSPF FAPM sub-TLV MAY appear multiple times in its parent TLV.
If it appears more than once with the same Flex-Algorithm value, the If it appears more than once with the same Flex-Algorithm value, the
first instance MUST be used and any subsequent instances MUST be first instance MUST be used and any subsequent instances MUST be
ignored. ignored.
The usage of the Flex-Algorithm prefix metric is described in The usage of the Flex-Algorithm prefix metric is described in
Section 13. Section 13.
10. OSPF Flexible Algorithm ASBR Reachability Advertisement 10. OSPF Flexible Algorithm ASBR Reachability Advertisement
An OSPF ABR advertises the reachability of ASBRs in its attached An OSPF ABR advertises the reachability of ASBRs in its attached
areas to enable routers within those areas to perform route areas to enable routers within those areas to perform route
calculations for external prefixes advertised by the ASBRs. OSPF calculations for external prefixes advertised by the ASBRs. OSPF
extensions for advertisement of Flex-Algorithm specific reachability extensions for advertisement of Flex-Algorithm-specific reachability
and metric for ASBRs is similarly required for Flex-Algorithm and the metric for ASBRs is similarly required for Flex-Algorithm
external prefix computations as described further in Section 13.1. external prefix computations, as described further in Section 13.1.
10.1. OSPFv2 Extended Inter-Area ASBR LSA 10.1. OSPFv2 Extended Inter-Area ASBR LSA
The OSPFv2 Extended Inter-Area ASBR (EIA-ASBR) LSA is an OSPF Opaque The OSPFv2 Extended Inter-Area ASBR (EIA-ASBR) LSA is an OSPF Opaque
LSA [RFC5250] that is used to advertise additional attributes related LSA [RFC5250] that is used to advertise additional attributes related
to the reachability of the OSPFv2 ASBR that is external to the area to the reachability of the OSPFv2 ASBR that is external to the area
yet internal to the OSPF domain. Semantically, the OSPFv2 EIA-ASBR yet internal to the OSPF domain. Semantically, the OSPFv2 EIA-ASBR
LSA is equivalent to the fixed format Type 4 Summary LSA [RFC2328]. LSA is equivalent to the fixed format Type 4 summary-LSA [RFC2328].
Unlike the Type 4 Summary LSA, the LSID of the EIA-ASBR LSA does not Unlike the Type 4 summary-LSA, the Link State ID (LSID) of the EIA-
carry the ASBR Router-ID - the ASBR Router-ID is carried in the body ASBR LSA does not carry the ASBR Router ID -- the ASBR Router ID is
of the LSA. The OSPFv2 EIA-ASBR LSA is advertised by an OSPFv2 ABR carried in the body of the LSA. The OSPFv2 EIA-ASBR LSA is
and its flooding is defined to be area-scoped only. advertised by an OSPFv2 ABR, and its flooding is defined to be area-
scoped only.
An OSPFv2 ABR generates the EIA-ASBR LSA for an ASBR when it is An OSPFv2 ABR generates the EIA-ASBR LSA for an ASBR when it is
advertising the Type-4 Summary LSA for it and has the need for advertising the Type 4 summary-LSA for it and has the need for
advertising additional attributes for that ASBR beyond what is advertising additional attributes for that ASBR beyond what is
conveyed in the fixed format Type-4 Summary LSA. An OSPFv2 ABR MUST conveyed in the fixed-format Type 4 summary-LSA. An OSPFv2 ABR MUST
NOT advertise the EIA-ASBR LSA for an ASBR for which it is not NOT advertise the EIA-ASBR LSA for an ASBR for which it is not
advertising the Type 4 Summary LSA. This ensures that the ABR does advertising the Type 4 summary-LSA. This ensures that the ABR does
not generate the EIA-ASBR LSA for an ASBR to which it does not have not generate the EIA-ASBR LSA for an ASBR to which it does not have
reachability in the base OSPFv2 topology calculation. The OSPFv2 ABR reachability in the base OSPFv2 topology calculation. The OSPFv2 ABR
SHOULD NOT advertise the EIA-ASBR LSA for an ASBR when it does not SHOULD NOT advertise the EIA-ASBR LSA for an ASBR when it does not
have additional attributes to advertise for that ASBR. have additional attributes to advertise for that ASBR.
The OSPFv2 EIA-ASBR LSA has the following format: The OSPFv2 EIA-ASBR LSA has the following format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | LS Type | | LS age | Options | LS Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque Type | Opaque ID | | Opaque Type | Opaque ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router | | Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number | | LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | Length | | LS checksum | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+- TLVs -+ +- TLVs -+
| ... | | ... |
LS age and Options fields are as defined in Section A.4.1. of The LS age and Options fields are as defined in Appendix A.4.1 of
[RFC2328]. [RFC2328].
The LS Type MUST be 10, indicating that the Opaque LSA flooding scope The LS Type MUST be 10, indicating that the Opaque LSA flooding scope
is area-local [RFC5250]. is area-local [RFC5250].
The Opaque Type used by the OSPFv2 EIA-ASBR LSA is 11. The Opaque The Opaque Type used by the OSPFv2 EIA-ASBR LSA is 11. The Opaque
Type is used to differentiate the various types of OSPFv2 Opaque LSAs Type is used to differentiate the various types of OSPFv2 Opaque LSAs
and is described in Section 3 of [RFC5250]. and is described in Section 3 of [RFC5250].
The Opaque ID field is an arbitrary value used to maintain multiple The Opaque ID field is an arbitrary value used to maintain multiple
OSPFv2 EIA-ASBR LSAs. For OSPFv2 EIA-ASBR LSAs, the Opaque ID has no OSPFv2 EIA-ASBR LSAs. For OSPFv2 EIA-ASBR LSAs, the Opaque ID has no
semantic significance other than to differentiate OSPFv2 EIA-ASBR semantic significance other than to differentiate OSPFv2 EIA-ASBR
LSAs originated by the same OSPFv2 ABR. If multiple OSPFv2 EIA-ASBR LSAs originated by the same OSPFv2 ABR. If multiple OSPFv2 EIA-ASBR
LSAs specify the same ASBR, the attributes from the Opaque LSA with LSAs specify the same ASBR, the attributes from the Opaque LSA with
the lowest Opaque ID SHOULD be used. the lowest Opaque ID SHOULD be used.
Advertising Router, LS sequence number, and LS checksum fields are as The Advertising Router, LS sequence number, and LS checksum fields
defined in Section A.4.1. of [RFC2328]. are as defined in Appendix A.4.1 of [RFC2328].
The Length field is as defined in Section A.4.1. of [RFC5250]. It The Length field is as defined in Appendix A.4.1 of [RFC2328]. It
represents the total length (in octets) of the Opaque LSA, including represents the total length (in octets) of the Opaque LSA, including
the LSA header and all TLVs (including padding). the LSA header and all TLVs (including padding).
The format of the TLVs within the body of the OSPFv2 EIA-ASBR LSA is The format of the TLVs within the body of the OSPFv2 EIA-ASBR LSA is
the same as the format used by the Traffic Engineering Extensions to the same as the format used by the Traffic Engineering Extensions to
OSPFv2 [RFC3630]. The variable TLV section consists of one or more OSPFv2 [RFC3630]. The variable TLV section consists of one or more
nested TLV tuples. Nested TLVs are also referred to as sub- TLVs. nested TLV tuples. Nested TLVs are also referred to as sub-TLVs.
The TLV Length field defines the length of the value portion in The TLV Length field defines the length of the value portion in
octets (thus, a TLV with no value portion would have a length of 0). octets (thus, a TLV with no value portion would have a length of 0).
The TLV is padded to 4-octet alignment; padding is not included in The TLV is padded to 4-octet alignment; padding is not included in
the Length field (so a 3-octet value would have a length of 3, but the Length field (so a 3-octet value would have a length of 3, but
the total size of the TLV would be 8 octets). Nested TLVs are also the total size of the TLV would be 8 octets). Nested TLVs are also
32-bit aligned. For example, a 1-octet value would have the Length 32-bit aligned. For example, a 1-octet value would have the Length
field set to 1, and 3 octets of padding would be added to the end of field set to 1, and 3 octets of padding would be added to the end of
the value portion of the TLV. The padding is composed of zeros. the value portion of the TLV. The padding is composed of zeros.
10.1.1. OSPFv2 Extended Inter-Area ASBR TLV 10.1.1. OSPFv2 Extended Inter-Area ASBR TLV
The OSPFv2 Extended Inter-Area ASBR (EIA-ASBR) TLV is a top-level TLV The OSPFv2 Extended Inter-Area ASBR (EIA-ASBR) TLV is a top-level TLV
of the OSPFv2 EIA-ASBR LSA and is used to advertise additional of the OSPFv2 EIA-ASBR LSA and is used to advertise additional
attributes associated with the reachability of an ASBR. attributes associated with the reachability of an ASBR.
The OSPFv2 EIA-ASBR TLV has the following format: The OSPFv2 EIA-ASBR TLV has the following format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ASBR Router ID | | ASBR Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. . . .
. Sub-TLVs . . Sub-TLVs .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where: where:
Type: 1
Type: 1 Length: variable number of octets.
Length: variable number of octets
ASBR Router ID: four octets carrying the OSPF Router ID of the ASBR Router ID: 4 octets carrying the OSPF Router ID of the ASBR
ASBR whose information is being carried. whose information is being carried.
Sub-TLVs : variable Sub-TLVs: variable
Only a single OSPFv2 EIA-ASBR TLV MUST be advertised in each OSPFv2 Only a single OSPFv2 EIA-ASBR TLV MUST be advertised in each OSPFv2
EIA-ASBR LSA and the receiver MUST ignore all instances of this TLV EIA-ASBR LSA, and the receiver MUST ignore all instances of this TLV
other than the first one in an LSA. other than the first one in an LSA.
OSPFv2 EIA-ASBR TLV MUST be present inside an OSPFv2 EIA-ASBR LSA and The OSPFv2 EIA-ASBR TLV MUST be present inside an OSPFv2 EIA-ASBR LSA
MUST include at least a single sub-TLV, otherwise the OSPFv2 EIA-ASBR and MUST include at least a single sub-TLV; otherwise, the OSPFv2
LSA MUST be ignored by the receiver. EIA-ASBR LSA MUST be ignored by the receiver.
10.2. OSPF Flexible Algorithm ASBR Metric Sub-TLV 10.2. OSPF Flexible Algorithm ASBR Metric Sub-TLV
The OSPF Flexible Algorithm ASBR Metric (FAAM) Sub-TLV supports the The OSPF Flexible Algorithm ASBR Metric (FAAM) sub-TLV supports the
advertisement of a Flex-Algorithm specific metric associated with a advertisement of a Flex-Algorithm-specific metric associated with a
given ASBR reachability advertisement by an ABR. given ASBR reachability advertisement by an ABR.
The OSPF Flex-Algorithm ASBR Metric (FAAM) Sub-TLV is a Sub-TLV of The OSPF FAAM sub-TLV is a sub-TLV of the:
the:
- OSPFv2 Extended Inter-Area ASBR TLV as defined in Section 10.1.1 * OSPFv2 Extended Inter-Area ASBR TLV, as defined in Section 10.1.1,
and
- OSPFv3 Inter-Area-Router TLV defined in [RFC8362] * OSPFv3 Inter-Area-Router TLV, as defined in [RFC8362].
OSPF FAAM Sub-TLV has the following format: The OSPF FAAM sub-TLV has the following format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Flex-Algorithm | Reserved | |Flex-Algorithm | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric | | Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where: where:
Type: 1 for OSPFv2, and 33 for OSPFv3
Type: 1 for OSPFv2, 33 for OSPFv3 Length: 8 octets
Length: 8 octets
Flex-Algorithm: Single octet value between 128 and 255 inclusive. Flex-Algorithm: single octet value between 128 and 255 inclusive.
Reserved: Three octets. MUST be set to 0, ignored at reception. Reserved: 3 octets. MUST be set to 0 and ignored at reception.
Metric: 4 octets of metric information Metric: 4 octets of metric information.
The OSPF FAAM Sub-TLV MAY appear multiple times in its parent TLV. The OSPF FAAM sub-TLV MAY appear multiple times in its parent TLV.
If it appears more than once with the same Flex-Algorithm value, the If it appears more than once with the same Flex-Algorithm value, the
first instance MUST be used and any subsequent instances MUST be first instance MUST be used and any subsequent instances MUST be
ignored. ignored.
The advertisement of the ASBR reachability using the OSPF FAAM Sub- The advertisement of the ASBR reachability using the OSPF FAAM sub-
TLV inside the OSPFv2 EIA-ASBR LSA follows Section 12.4.3 of TLV inside the OSPFv2 EIA-ASBR LSA follows Section 12.4.3 of
[RFC2328] and inside the OSPFv3 E-Inter-Area-Router LSA follows [RFC2328] and inside the OSPFv3 E-Inter-Area-Router-LSA follows
Section 4.8.5 of [RFC5340]. The reachability of the ASBR is Section 4.8.5 of [RFC5340]. The reachability of the ASBR is
evaluated in the context of the specific Flex-Algorithm. evaluated in the context of the specific Flex-Algorithm.
The FAAM computed by the ABR will be equal to the metric to reach the The FAAM computed by the ABR will be equal to the metric to reach the
ASBR for a given Flex-Algorithm in a source area or the cumulative ASBR for a given Flex-Algorithm in a source area or the cumulative
metric via other ABR(s) when the ASBR is in a remote area. This is metric via an ABR(s) when the ASBR is in a remote area. This is
similar in nature to how the metric is set when the ASBR reachability similar in nature to how the metric is set when the ASBR reachability
metric is computed in the default algorithm for the metric in the metric is computed in the default algorithm for the metric in the
OSPFv2 Type 4 ASBR Summary LSA and the OSPFv3 Inter-Area-Router LSA. OSPFv2 Type 4 ASBR summary-LSA and the OSPFv3 Inter-Area-Router-LSA.
An OSPF ABR MUST NOT include the OSPF FAAM Sub-TLV with a specific An OSPF ABR MUST NOT include the OSPF FAAM sub-TLV with a specific
Flex-Algorithm in its reachability advertisement for an ASBR between Flex-Algorithm in its reachability advertisement for an ASBR between
areas unless that ASBR is reachable for it in the context of that areas unless that ASBR is reachable for it in the context of that
specific Flex-Algorithm. specific Flex-Algorithm.
An OSPF ABR MUST include the OSPF FAAM Sub-TLVs as part of the ASBR An OSPF ABR MUST include the OSPF FAAM sub-TLVs as part of the ASBR
reachability advertisement between areas for any Flex-Algorithm for reachability advertisement between areas for any Flex-Algorithm for
which the winning FAD includes the M-flag and the ASBR is reachable which the winning FAD includes the M-flag and the ASBR is reachable
in the context of that specific Flex-Algorithm. in the context of that specific Flex-Algorithm.
OSPF routers MUST use the OSPF FAAM Sub-TLV to calculate the OSPF routers MUST use the OSPF FAAM sub-TLV to calculate the
reachability of the ASBRs if the winning FAD for the specific Flex- reachability of the ASBRs if the winning FAD for the specific Flex-
Algorithm includes the M-flag. OSPF routers MUST NOT use the OSPF Algorithm includes the M-flag. OSPF routers MUST NOT use the OSPF
FAAM Sub-TLV to calculate the reachability of the ASBRs for the FAAM sub-TLV to calculate the reachability of the ASBRs for the
specific Flex-Algorithm if the winning FAD for such Flex-Algorithm specific Flex-Algorithm if the winning FAD for such Flex-Algorithm
does not include the M-flag. Instead, the OSPFv2 Type 4 Summary LSAs does not include the M-flag. Instead, the OSPFv2 Type 4 summary-LSAs
or the OSPFv3 Inter-Area-Router-LSAs MUST be used instead as or the OSPFv3 Inter-Area-Router-LSAs MUST be used, as specified in
specified in section 16.2 of [RFC2328] and section 4.8.5 of [RFC5340] Section 16.2 of [RFC2328] and Section 4.8.5 of [RFC5340] for OSPFv2
for OSPFv2 and OSPFv3 respectively. and OSPFv3, respectively.
The processing of a new or changed OSPF FAAM Sub-TLV triggers the The processing of a new or changed OSPF FAAM sub-TLV triggers the
processing of External routes similar to what is described in section processing of external routes similar to what is described in
16.5 of the [RFC2328] for OSPFv2 and section 4.8.5 of [RFC5340] for Section 16.5 of [RFC2328] for OSPFv2 and Section 4.8.5 of [RFC5340]
OSPFv3 for the specific Flex-Algorithm. The External and NSSA for OSPFv3 for the specific Flex-Algorithm. The OSPF external and
External route calculation should be limited to Flex-Algorithm(s) for NSSA external route calculation should be limited to a Flex-
which the winning FAD(s) includes the M-flag. Algorithm(s) for which the winning FAD(s) includes the M-flag.
Processing of the OSPF FAAM Sub-TLV does not require the existence of Processing of the OSPF FAAM sub-TLV does not require the existence of
the equivalent OSPFv2 Type 4 Summary LSA or the OSPFv3 Inter-Area- the equivalent OSPFv2 Type 4 summary-LSA or the OSPFv3 Inter-Area-
Router-LSA that is advertised by the same ABR inside the area. The Router-LSA that is advertised by the same ABR inside the area. The
presence of the base LSA is not mandatory for the usage of the presence of the base LSA is not mandatory for the usage of the
extended LSA with the OSPF FAAM Sub-TLV. extended LSA with the OSPF FAAM sub-TLV.
11. Advertisement of Node Participation in a Flex-Algorithm 11. Advertisement of Node Participation in a Flex-Algorithm
When a router is configured to participate in a particular Flex- When a router is configured to participate in a particular Flex-
Algorithm and is advertising such participation, it is participating Algorithm and is advertising such participation, it is participating
in that Flex-Algorithm. in that Flex-Algorithm.
Paths for various data-planes MAY be computed for a specific Flex- Paths for various data planes MAY be computed for a specific Flex-
Algorithm. Each data-plane uses its own specific forwarding over Algorithm. Each data plane uses its own specific forwarding over
such Flex-Algorithm paths. To guarantee the presence of the data- such Flex-Algorithm paths. To guarantee the presence of the data-
plane specific forwarding, associated with a particular Flex- plane-specific forwarding, associated with a particular Flex-
Algorithm, a router MUST advertise its participation for a particular Algorithm, a router MUST advertise its participation for a particular
Flex-Algorithm for each data-plane. Some data-planes may share a Flex-Algorithm for each data plane. Some data planes may share a
common participation advertisement (e.g. SR-MPLS and SRv6). common participation advertisement (e.g., SR-MPLS and SRv6).
Advertisement of the participation for any particular Flex-Algorithm Advertisement of the participation for any particular Flex-Algorithm
in any data-plane is subject to the condition specified in in any data plane is subject to the condition specified in
Section 5.3. Section 5.3.
11.1. Advertisement of Node Participation for Segment Routing 11.1. Advertisement of Node Participation for Segment Routing
[RFC8667], [RFC8665], and [RFC8666] (IGP Segment Routing extensions) [RFC8665], [RFC8666], and [RFC8667] (IGP Segment Routing extensions)
describe how the SR-Algorithm is used to compute the IGP best path. describe how the SR-Algorithm is used to compute the IGP best path.
Routers advertise support for the SR-Algorithm as a node capability Routers advertise support for the SR-Algorithm as a node capability,
as described in the above-mentioned IGP Segment Routing extensions. as described in the above-mentioned IGP Segment Routing extensions.
To advertise participation for a particular Flex-Algorithm for To advertise participation for a particular Flex-Algorithm for
Segment Routing, including both SR-MPLS and SRv6, the Flex-Algorithm Segment Routing, including both SR-MPLS and SRv6, the Flex-Algorithm
value MUST be advertised in the SR-Algorithm TLV (OSPF) or sub-TLV value MUST be advertised in the SR-Algorithm TLV (OSPF) or sub-TLV
(IS-IS). (IS-IS).
Segment Routing Flex-Algorithm participation advertisement is Segment Routing Flex-Algorithm participation advertisement is
topology independent. When a router advertises participation in an topology independent. When a router advertises participation in an
SR-Algorithm, the participation applies to all topologies in which SR-Algorithm, the participation applies to all topologies in which
the advertising node participates. the advertising node participates.
11.2. Advertisement of Node Participation for Other Data-planes 11.2. Advertisement of Node Participation for Other Data Planes
This section describes considerations related to how other data- This section describes considerations related to how other data
planes can advertise their participation in a specific Flex- planes can advertise their participation in a specific Flex-
Algorithm. Algorithm.
Data-plane specific Flex-Algorithm participation advertisements MAY Data-plane-specific Flex-Algorithm participation advertisements MAY
be topology specific or MAY be topology independent, depending on the be topology specific or MAY be topology independent, depending on the
data-plane itself. data plane itself.
Data-plane specific advertisement for Flex-Algorithm participation Data-plane-specific advertisement for Flex-Algorithm participation
MUST be defined for each data-plane and is outside the scope of this MUST be defined for each data plane and is outside the scope of this
document. document.
12. Advertisement of Link Attributes for Flex-Algorithm 12. Advertisement of Link Attributes for Flex-Algorithm
Various link attributes may be used during the Flex-Algorithm path Various link attributes may be used during the Flex-Algorithm path
calculation. For example, include or exclude rules based on link calculation. For example, include or exclude rules based on link
affinities can be part of the Flex-Algorithm definition as defined in affinities can be part of the Flex-Algorithm Definition, as defined
Section 6 and Section 7. in Sections 6 and 7.
Application-specific link attributes, as specified in [RFC8919] or Application-specific link attributes, as specified in [RFC8919] or
[RFC8920], that are to be used during Flex-Algorithm calculation MUST [RFC8920], that are to be used during Flex-Algorithm calculation MUST
use the Application-Specific Link Attribute (ASLA) advertisements use the Application-Specific Link Attribute (ASLA) advertisements
defined in [RFC8919] or [RFC8920], unless, in the case of IS-IS, the defined in [RFC8919] or [RFC8920] unless, in the case of IS-IS, the
L-Flag is set in the ASLA advertisement. When the L-Flag is set, L-flag is set in the ASLA advertisement. When the L-flag is set,
then legacy advertisements MUST be used, subject to the procedures then legacy advertisements MUST be used, subject to the procedures
and constraints defined in [[RFC8919] Section 4.2 and Section 6. and constraints defined in Section 4.2 of [RFC8919] and Section 6.
The mandatory use of ASLA advertisements applies to link attributes The mandatory use of ASLA advertisements applies to link attributes
specifically mentioned in this document (Min Unidirectional Link specifically mentioned in this document (Min Unidirectional Link
Delay, TE Default Metric, Administrative Group, Extended Delay, TE Default Metric, Administrative Group, Extended
Administrative Group and Shared Risk Link Group) and any other link Administrative Group, and Shared Risk Link Group) and any other link
attributes that may be used in support of Flex-Algorithm in the attributes that may be used in support of Flex-Algorithm in the
future. future.
A new Application Identifier Bit is defined to indicate that the ASLA A new Application Identifier Bit is defined to indicate that the ASLA
advertisement is associated with the Flex-Algorithm application. advertisement is associated with the Flex-Algorithm application.
This bit is set in the Standard Application Bit Mask (SABM) defined This bit is set in the Standard Application Bit Mask (SABM) defined
in [RFC8919] or [RFC8920]: in [RFC8919] or [RFC8920]:
Bit-3: Flexible Algorithm (X-bit) Bit 3: Flexible Algorithm (X-bit)
ASLA Admin Group Advertisements to be used by the Flexible Algorithm ASLA Admin Group Advertisements to be used by the Flexible Algorithm
application MAY use either the Administrative Group or Extended application MAY use either the Administrative Group or Extended
Administrative Group encodings. Administrative Group encodings.
A receiver supporting this specification MUST accept both ASLA A receiver supporting this specification MUST accept both ASLA
Administrative Group and Extended Administrative Group TLVs as Administrative Group and Extended Administrative Group TLVs, as
defined in [RFC8919] or [RFC8920]. In the case of IS-IS, if the defined in [RFC8919] or [RFC8920]. In the case of IS-IS, if the
L-Flag is set in ASLA advertisement, as defined in [RFC8919] L-flag is set in the ASLA advertisement, as defined in Section 4.2 of
Section 4.2, then the receiver MUST be able to accept both [RFC8919], then the receiver MUST be able to accept both the
Administrative Group TLV as defined in [RFC5305] and Extended Administrative Group TLV, as defined in [RFC5305], and the Extended
Administrative Group TLV as defined in [RFC7308]. Administrative Group TLV, as defined in [RFC7308].
13. Calculation of Flexible Algorithm Paths 13. Calculation of Flexible Algorithm Paths
A router MUST be configured to participate in a given Flex-Algorithm A router MUST be configured to participate in a given Flex-Algorithm
K and MUST select the FAD based on the rules defined in Section 5.3 K and MUST select the FAD based on the rules defined in Section 5.3
before it can compute any path for that Flex-Algorithm. before it can compute any path for that Flex-Algorithm.
No specific two-way connectivity check is performed during the Flex- No specific two-way connectivity check is performed during the Flex-
Algorithm path computation. The result of the existing, Flex- Algorithm path computation. The result of the existing Flex-
Algorithm agnostic, two-way connectivity check is used during the Algorithm-agnostic, two-way connectivity check is used during the
Flex-Algorithm path computation. Flex-Algorithm path computation.
As described in Section 11, participation for any particular Flex- As described in Section 11, participation for any particular Flex-
Algorithm MUST be advertised on a per data-plane basis. Calculation Algorithm MUST be advertised on a per data plane basis. Calculation
of the paths for any particular Flex-Algorithm is data-plane of the paths for any particular Flex-Algorithm is data plane
specific. specific.
Multiple data-planes MAY use the same Flex-Algorithm value at the Multiple data planes MAY use the same Flex-Algorithm value at the
same time, and as such, share the FAD for it. Traffic for each data- same time and, as such, share the FAD for it. Traffic for each data
plane will be forwarded based on the data-plane specific forwarding plane will be forwarded based on the data-plane-specific forwarding
entries. entries.
Flex-Algorithm definition is data-plane independent and is used by The Flex-Algorithm Definition is data plane independent and is used
all Flex-Algorithm data-planes. by all Flex-Algorithm data planes.
The way various data-planes handle nodes that do not participate in The way various data planes handle nodes that do not participate in
Flexible Algorithm is data-plane specific. If the data-plane only Flexible Algorithm is data plane specific. If the data plane only
wants to consider participating nodes during the Flex-Algorithm wants to consider participating nodes during the Flex-Algorithm
calculation, then when computing paths for a given Flex-Algorithm, calculation, then when computing paths for a given Flex-Algorithm,
all nodes that do not advertise participation for that Flex-Algorithm all nodes that do not advertise participation for that Flex-Algorithm
in their data-plane specific advertisements MUST be pruned from the in their data-plane-specific advertisements MUST be pruned from the
topology. Segment Routing, including both SR-MPLS and SRv6, are topology. Segment Routing, including both SR-MPLS and SRv6, are data
data-planes that MUST use such pruning when computing Flex-Algorithm planes that MUST use such pruning when computing Flex-Algorithm
paths. paths.
When computing the path for a given Flex-Algorithm, the metric-type When computing the path for a given Flex-Algorithm, the metric-type
that is part of the Flex-Algorithm definition (Section 5) MUST be that is part of the Flex-Algorithm Definition (Section 5) MUST be
used. used.
When computing the path for a given Flex-Algorithm, the calculation- When computing the path for a given Flex-Algorithm, the calculation-
type that is part of the Flex-Algorithm definition (Section 5) MUST type that is part of the Flex-Algorithm Definition (Section 5) MUST
be used. be used.
Various link include or exclude rules can be part of the Flex- Various links that include or exclude rules can be part of the Flex-
Algorithm definition. To refer to a particular bit within an Admin Algorithm Definition. To refer to a particular bit within an Admin
Group or Extended Admin Group we use the term 'color'. Group or Extended Admin Group, we use the term "color".
Rules, in the order as specified below, MUST be used to prune links Rules, in the order as specified below, MUST be used to prune links
from the topology during the Flex-Algorithm computation. from the topology during the Flex-Algorithm computation.
For all links in the topology: For all links in the topology:
1. Check if any exclude AG rule is part of the Flex-Algorithm 1. Check if any exclude Administrative Group rule is part of the
definition. If such exclude rule exists, check if any color that Flex-Algorithm Definition. If such exclude rule exists, check if
is part of the exclude rule is also set on the link. If such a any color that is part of the exclude rule is also set on the
color is set, the link MUST be pruned from the computation. link. If such a color is set, the link MUST be pruned from the
computation.
2. Check if any exclude SRLG rule is part of the Flex-Algorithm 2. Check if any exclude SRLG rule is part of the Flex-Algorithm
definition. If such exclude rule exists, check if the link is Definition. If such exclude rule exists, check if the link is
part of any SRLG that is also part of the SRLG exclude rule. If part of any SRLG that is also part of the SRLG exclude rule. If
the link is part of such SRLG, the link MUST be pruned from the the link is part of such SRLG, the link MUST be pruned from the
computation. computation.
3. Check if any include-any AG rule is part of the Flex-Algorithm 3. Check if any include-any Administrative Group rule is part of the
definition. If such include-any rule exists, check if any color Flex-Algorithm Definition. If such include-any rule exists,
that is part of the include-any rule is also set on the link. If check if any color that is part of the include-any rule is also
no such color is set, the link MUST be pruned from the set on the link. If no such color is set, the link MUST be
computation. pruned from the computation.
4. Check if any include-all AG rule is part of the Flex-Algorithm 4. Check if any include-all Administrative Group rule is part of the
definition. If such include-all rule exists, check if all colors Flex-Algorithm Definition. If such include-all rule exists,
that are part of the include-all rule are also set on the link. check if all colors that are part of the include-all rule are
If all such colors are not set on the link, the link MUST be also set on the link. If all such colors are not set on the
pruned from the computation. link, the link MUST be pruned from the computation.
5. If the Flex-Algorithm definition uses other than IGP metric 5. If the Flex-Algorithm Definition uses something other than the
(Section 5), and such metric is not advertised for the particular IGP metric (Section 5), and such metric is not advertised for the
link in a topology for which the computation is done, such link particular link in a topology for which the computation is done,
MUST be pruned from the computation. A metric of value 0 MUST NOT such link MUST be pruned from the computation. A metric of value
be assumed in such a case. 0 MUST NOT be assumed in such a case.
13.1. Multi-area and Multi-domain Considerations 13.1. Multi-area and Multi-domain Considerations
Any IGP Shortest Path Tree calculation is limited to a single area. Any IGP Shortest Path Tree calculation is limited to a single area.
This applies to Flex-Algorithm calculations as well. Given that the This applies to Flex-Algorithm calculations as well. Given that the
computing router does not have visibility of the topology of the next computing router does not have visibility of the topology of the next
areas or domain, the Flex-Algorithm specific path to an inter-area or areas or domain, the Flex-Algorithm-specific path to an inter-area or
inter-domain prefix will be computed for the local area only. The inter-domain prefix will be computed for the local area only. The
egress L1/L2 router (ABR in OSPF), or ASBR for inter-domain case, egress L1/L2 router (ABR in OSPF), or ASBR for an inter-domain case,
will be selected based on the best path for the given Flex-Algorithm will be selected based on the best path for the given Flex-Algorithm
in the local area and such egress ABR or ASBR router will be in the local area, and such egress ABR or ASBR router will be
responsible to compute the best Flex-Algorithm specific path over the responsible to compute the best Flex-Algorithm-specific path over the
next area or domain. This may produce an end-to-end path, which is next area or domain. This may produce an end-to-end path, which is
suboptimal based on Flex-Algorithm constraints. In cases where the suboptimal based on Flex-Algorithm constraints. In cases where the
ABR or ASBR has no reachability to a prefix for a given Flex- ABR or ASBR has no reachability to a prefix for a given Flex-
Algorithm in the next area or domain, the traffic could be dropped by Algorithm in the next area or domain, the traffic could be dropped by
the ABR/ASBR. the ABR/ASBR.
To allow the optimal end-to-end path for an inter-area or inter- To allow the optimal end-to-end path for an inter-area or inter-
domain prefix for any Flex-Algorithm to be computed, the FAPM has domain prefix for any Flex-Algorithm to be computed, the FAPM has
been defined in Section 8 and Section 9. For external route been defined in Sections 8 and 9. For external route calculation for
calculation for prefixes originated by ASBRs in remote areas in OSPF, prefixes originated by ASBRs in remote areas in OSPF, the FAAM has
the FAAM has been defined in Section 10.2 for the ABR to indicate its been defined in Section 10.2 for the ABR to indicate its ASBR
ASBR reachability along with the metric for the specific Flex- reachability along with the metric for the specific Flex-Algorithm.
Algorithm.
If the FAD selected based on the rules defined in Section 5.3 If the FAD selected based on the rules defined in Section 5.3
includes the M-flag, an ABR or ASBR MUST include the FAPM (Section 8, includes the M-flag, an ABR or an ASBR MUST include the FAPM (see
Section 9) when advertising the prefix, that is reachable in a given Sections 8 and 9) when advertising the prefix that is reachable in a
Flex-Algorithm, between areas or domains. Such metric will be equal given Flex-Algorithm between areas or domains. Such metric will be
to the metric to reach the prefix for that Flex-Algorithm in its equal to the metric to reach the prefix for that Flex-Algorithm in
source area or domain. This is similar in nature to how the metric its source area or domain. This is similar in nature to how the
is set when prefixes are advertised between areas or domains for the metric is set when prefixes are advertised between areas or domains
default algorithm. When a prefix is unreachable in its source area for the default algorithm. When a prefix is unreachable in its
or domain in a specific Flex-Algorithm, then an ABR or ASBR MUST NOT source area or domain in a specific Flex-Algorithm, then an ABR or
include the FAPM for that Flex-Algorithm when advertising the prefix ASBR MUST NOT include the FAPM for that Flex-Algorithm when
between areas or domains. advertising the prefix between areas or domains.
If the FAD selected based on the rules defined in Section 5.3 If the FAD selected based on the rules defined in Section 5.3
includes the M-flag, the FAPM MUST be used during the calculation of includes the M-flag, the FAPM MUST be used during the calculation of
prefix reachability for the inter-area and external prefixes. If the prefix reachability for the inter-area and external prefixes. If the
FAPM for the Flex-Algorithm is not advertised with the inter-area or FAPM for the Flex-Algorithm is not advertised with the inter-area or
external prefix reachability advertisement, the prefix MUST be external prefix reachability advertisement, the prefix MUST be
considered as unreachable for that Flex-Algorithm. Similarly, in the considered as unreachable for that Flex-Algorithm. Similarly, in the
case of OSPF, for ASBRs in remote areas, if the FAAM is not case of OSPF, for ASBRs in remote areas, if the FAAM is not
advertised by the local ABR(s), the ASBR MUST be considered as advertised by the local ABR(s), the ASBR MUST be considered as
unreachable for that Flex-Algorithm and the external prefix unreachable for that Flex-Algorithm, and the external prefix
advertisements from such an ASBR are not considered for that Flex- advertisements from such an ASBR are not considered for that Flex-
Algorithm. Algorithm.
Flex-Algorithm prefix metrics and the OSPF Flex-Algorithm ASBR The Flex-Algorithm prefix metrics and the OSPF Flex-Algorithm ASBR
metrics MUST NOT be used during the Flex-Algorithm computation unless metrics MUST NOT be used during the Flex-Algorithm computation unless
the FAD selected based on the rules defined in Section 5.3 includes the FAD selected based on the rules defined in Section 5.3 includes
the M-Flag, as described in (Section 6.4 or Section 7.4). the M-flag, as described in Sections 6.4 or 7.4.
In the case of OSPF, when calculating external routes in a Flex- In the case of OSPF, when calculating external routes in a Flex-
Algorithm, if the winning FAD includes the M-Flag, and where the Algorithm, if the winning FAD includes the M-flag, and the
advertising ASBR is in a remote area, the metric will be the sum of advertising ASBR is in a remote area, the metric will be the sum of
the following: the following:
* the FAPM for that Flex-Algorithm advertised with the external * the FAPM for that Flex-Algorithm advertised with the external
route by the ASBR route by the ASBR
* the metric to reach the ASBR for that Flex-Algorithm from the * the metric to reach the ASBR for that Flex-Algorithm from the
local ABR i.e., the FAAM for that Flex-Algorithm advertised by the local ABR, i.e., the FAAM for that Flex-Algorithm advertised by
ABR in the local area for that ASBR the ABR in the local area for that ASBR
* the Flex-Algorithm specific metric to reach the local ABR * the Flex-Algorithm-specific metric to reach the local ABR
This is similar in nature to how the metric is calculated for routes This is similar in nature to how the metric is calculated for routes
learned from remote ASBRs in the default algorithm using the OSPFv2 learned from remote ASBRs in the default algorithm using the OSPFv2
Type 4 ASBR Summary LSA and the OSPFv3 Inter-Area-Router LSA. Type 4 ASBR summary-LSA and the OSPFv3 Inter-Area-Router-LSA.
If the FAD selected based on the rules defined in Section 5.3 does If the FAD selected based on the rules defined in Section 5.3 does
not include the M-flag, then the IGP metrics associated with the not include the M-flag, then the IGP metrics associated with the
prefix reachability advertisements used by the base IS-IS and OSPF prefix reachability advertisements used by the base IS-IS and OSPF
protocol MUST be used for the Flex-Algorithm route computation. protocol MUST be used for the Flex-Algorithm route computation.
Similarly, in the case of external route calculations in OSPF, the Similarly, in the case of external route calculations in OSPF, the
ASBR reachability is determined based on the base OSPFv2 Type 4 ASBR reachability is determined based on the base OSPFv2 Type 4
Summary LSA and the OSFPv3 Inter-Area-Router LSA. summary-LSA and the OSFPv3 Inter-Area-Router-LSA.
It is NOT RECOMMENDED to use the Flex-Algorithm for inter-area or It is NOT RECOMMENDED to use the Flex-Algorithm for inter-area or
inter-domain prefix reachability without the M-flag set. The reason inter-domain prefix reachability without the M-flag set. The reason
is that without the explicit Flex-Algorithm Prefix Metric is that, without the explicit Flex-Algorithm prefix metric
advertisement (and the Flex-Algorithm ASBR metric advertisement in advertisement (and the Flex-Algorithm ASBR metric advertisement in
the case of OSPF external route calculation), it is not possible to the case of OSPF external route calculation), it is not possible to
conclude whether the ABR or ASBR has reachability to the inter-area conclude whether the ABR or ASBR has reachability to the inter-area
or inter-domain prefix for a given Flex-Algorithm in the next area or or inter-domain prefix for a given Flex-Algorithm in the next area or
domain. Sending the Flex-Algorithm traffic for such a prefix towards domain. Sending the Flex-Algorithm traffic for such a prefix towards
the ABR or ASBR may result in traffic looping or persistent traffic the ABR or ASBR may result in traffic looping or persistent traffic
drop. drop.
During the route computation, it is possible for the Flex-Algorithm During the route computation, it is possible for the Flex-Algorithm-
specific metric to exceed the maximum value that can be stored in an specific metric to exceed the maximum value that can be stored in an
unsigned 32-bit variable. In such scenarios, the value MUST be unsigned 32-bit variable. In such scenarios, the value MUST be
considered to be of value 0xFFFFFFFF during the computation and considered to be of value 0xFFFFFFFF during the computation and
advertised as such. advertised as such.
The FAPM MUST NOT be advertised with IS-IS L1 or L2 intra-area, The FAPM MUST NOT be advertised with IS-IS L1 or L2 intra-area,
OSPFv2 intra-area, or OSPFv3 intra-area routes. If the FAPM is OSPFv2 intra-area, or OSPFv3 intra-area routes. If the FAPM is
advertised for these route-types, it MUST be ignored during the advertised for these route-types, it MUST be ignored during the
prefix reachability calculation. prefix reachability calculation.
The M-flag in the FAD is not applicable to prefixes advertised as The M-flag in the FAD is not applicable to prefixes advertised as
SRv6 locators. The IS-IS SRv6 Locator TLV SRv6 locators. The IS-IS SRv6 Locator TLV [RFC9352] includes the
[I-D.ietf-lsr-isis-srv6-extensions] includes the Algorithm and Metric Algorithm and Metric fields. When the SRv6 Locator is advertised
fields. When the SRv6 Locator is advertised between areas or between areas or domains, the Metric field in the Locator TLV of IS-
domains, the metric field in the Locator TLV of IS-IS MUST be used IS MUST be used irrespective of the M-flag in the FAD advertisement.
irrespective of the M-flag in the FAD advertisement.
OSPF external and NSSA external prefix advertisements MAY include a OSPF external and NSSA external prefix advertisements MAY include a
non-zero forwarding address in the prefix advertisements in the base non-zero forwarding address in the prefix advertisements in the base
protocol. In such a scenario, the Flex-Algorithm specific protocol. In such a scenario, the Flex-Algorithm-specific
reachability of the external prefix is determined by Flex-Algorithm reachability of the external prefix is determined by Flex-Algorithm-
specific reachability of the forwarding address. specific reachability of the forwarding address.
In OSPF, the procedures for translation of NSSA external prefix In OSPF, the procedures for translation of NSSA external prefix
advertisements into external prefix advertisements performed by an advertisements into external prefix advertisements performed by an
NSSA ABR [RFC3101] remain unchanged for Flex-Algorithm. An NSSA NSSA ABR [RFC3101] remain unchanged for Flex-Algorithm. An NSSA
translator MUST include the OSPF FAPM Sub-TLVs for all Flex- translator MUST include the OSPF FAPM sub-TLVs for all Flex-
Algorithms that are in the original NSSA external prefix Algorithms that are in the original NSSA external prefix
advertisement from the NSSA ASBR in the translated external prefix advertisement from the NSSA ASBR in the translated external prefix
advertisement generated by it regardless of its participation in advertisement generated by it, regardless of its participation in
those Flex-Algorithms or its having reachability to the NSSA ASBR in those Flex-Algorithms or its having reachability to the NSSA ASBR in
those Flex-Algorithms. those Flex-Algorithms.
An area could become partitioned from the perspective of the Flex- An area could become partitioned from the perspective of the Flex-
Algorithm due to the constraints and/or metric being used for it, Algorithm due to the constraints and/or metric being used for it
while maintaining the continuity in the base algorithm. When that while maintaining the continuity in the base algorithm. When that
happens, some destinations inside that area could become unreachable happens, some destinations inside that area could become unreachable
in that Flex-Algorithm. These destinations will not be able to use in that Flex-Algorithm. These destinations will not be able to use
an inter-area path. This is the consequence of the fact that the an inter-area path. This is the consequence of the fact that the
inter-area prefix reachability advertisement would not be available inter-area prefix reachability advertisement would not be available
for these intra-area destinations within the area. It is RECOMMENDED for these intra-area destinations within the area. It is RECOMMENDED
to minimize the risk of such partitioning by providing enough to minimize the risk of such partitioning by providing enough
redundancy inside the area for each Flex-Algorithm being used. redundancy inside the area for each Flex-Algorithm being used.
14. Flex-Algorithm and Forwarding Plane 14. Flex-Algorithm and Forwarding Plane
This section describes how Flex-Algorithm paths are used in This section describes how Flex-Algorithm paths are used in
forwarding. forwarding.
14.1. Segment Routing MPLS Forwarding for Flex-Algorithm 14.1. Segment Routing MPLS Forwarding for Flex-Algorithm
This section describes how Flex-Algorithm paths are used with SR MPLS This section describes how Flex-Algorithm paths are used with SR MPLS
forwarding. forwarding.
Prefix SID advertisements include an SR-Algorithm value and, as such, Prefix-SID advertisements include an SR-Algorithm value and, as such,
are associated with the specified SR-Algorithm. Prefix-SIDs are also are associated with the specified SR-Algorithm. Prefix-SIDs are also
associated with a specific topology which is inherited from the associated with a specific topology that is inherited from the
associated prefix reachability advertisement. When the algorithm associated prefix reachability advertisement. When the algorithm
value advertised is a Flex-Algorithm value, the Prefix SID is value advertised is a Flex-Algorithm value, the Prefix-SID is
associated with paths calculated using that Flex-Algorithm in the associated with paths calculated using that Flex-Algorithm in the
associated topology. associated topology.
A Flex-Algorithm path MUST be installed in the MPLS forwarding plane A Flex-Algorithm path MUST be installed in the MPLS forwarding plane
using the MPLS label that corresponds to the Prefix-SID that was using the MPLS label that corresponds to the Prefix-SID that was
advertised for that Flex-algorithm. If the Prefix SID for a given advertised for that Flex-algorithm. If the Prefix-SID for a given
Flex-algorithm is not known, the Flex-Algorithm specific path cannot Flex-Algorithm is not known, the Flex-Algorithm-specific path cannot
be installed in the MPLS forwarding plane. be installed in the MPLS forwarding plane.
Traffic that is supposed to be routed via Flex-Algorithm specific Traffic that is supposed to be routed via Flex-Algorithm-specific
paths MUST be dropped when there are no such paths available. paths MUST be dropped when there are no such paths available.
Loop Free Alternate (LFA) paths ([RFC6571] or its variants) for a Loop Free Alternate (LFA) paths ([RFC6571] or its variants) for a
given Flex-Algorithm MUST be computed using the same constraints as given Flex-Algorithm MUST be computed using the same constraints as
the calculation of the primary paths for that Flex-Algorithm. LFA the calculation of the primary paths for that Flex-Algorithm. LFA
paths MUST only use Prefix-SIDs advertised specifically for the given paths MUST only use Prefix-SIDs advertised specifically for the given
algorithm. LFA paths MUST NOT use an Adjacency-SID that belongs to a algorithm. LFA paths MUST NOT use an Adjacency SID that belongs to a
link that has been pruned from the Flex-Algorithm computation. link that has been pruned from the Flex-Algorithm computation.
If LFA protection is being used to protect a given Flex-Algorithm If LFA protection is being used to protect a given Flex-Algorithm
paths, all routers in the area participating in the given Flex- path, all routers in the area participating in the given Flex-
Algorithm SHOULD advertise at least one Flex-Algorithm specific Node- Algorithm SHOULD advertise at least one Flex-Algorithm-specific Node-
SID. These Node-SIDs are used to steer traffic over the LFA computed SID. These Node-SIDs are used to steer traffic over the LFA-computed
backup path. backup path.
14.2. SRv6 Forwarding for Flex-Algorithm 14.2. SRv6 Forwarding for Flex-Algorithm
This section describes how Flex-Algorithm paths are used with SRv6 This section describes how Flex-Algorithm paths are used with SRv6
forwarding. forwarding.
In SRv6 a node is provisioned with a (topology, algorithm) specific In SRv6, a node is provisioned with a (topology, algorithm) specific
locator for each of the topology/algorithm pairs supported by that locator for each of the topology/algorithm pairs supported by that
node. Each locator is an aggregate prefix for all SIDs provisioned node. Each locator is an aggregate prefix for all SIDs provisioned
on that node which have the matching topology/algorithm. on that node that have the matching topology/algorithm.
The SRv6 locator advertisement in IS-IS The SRv6 locator advertisement in IS-IS [RFC9352] includes the Multi-
[I-D.ietf-lsr-isis-srv6-extensions] includes the MTID value that Topology Identifier (MTID) value that associates the locator with a
associates the locator with a specific topology. SRv6 locator specific topology. SRv6 locator advertisements also include an
advertisements also includes an Algorithm value that explicitly algorithm value that explicitly associates the locator with a
associates the locator with a specific algorithm. When the algorithm specific algorithm. When the algorithm value advertised with a
value advertised with a locator represents a Flex-Algorithm, the locator represents a Flex-Algorithm, the paths to the locator prefix
paths to the locator prefix MUST be calculated using the specified MUST be calculated using the specified Flex-Algorithm in the
Flex-Algorithm in the associated topology. associated topology.
Forwarding entries for the locator prefixes advertised in IS-IS MUST Forwarding entries for the locator prefixes advertised in IS-IS MUST
be installed in the forwarding plane of the receiving SRv6 capable be installed in the forwarding plane of the receiving SRv6-capable
routers when the associated topology/algorithm is participating in routers when the associated topology/algorithm is participating in
them. Forwarding entries for locators associated with Flex- them. Forwarding entries for locators associated with Flex-
Algorithms in which the node is not participating MUST NOT be Algorithms in which the node is not participating MUST NOT be
installed in the forwarding plane. installed in the forwarding plane.
When the locator is associated with a Flex-Algorithm, LFA paths to When the locator is associated with a Flex-Algorithm, LFA paths to
the locator prefix MUST be calculated using such Flex-Algorithm in the locator prefix MUST be calculated using such Flex-Algorithm in
the associated topology, to guarantee that they follow the same the associated topology to guarantee that they follow the same
constraints as the calculation of the primary paths. LFA paths MUST constraints as the calculation of the primary paths. LFA paths MUST
only use SRv6 SIDs advertised specifically for the given Flex- only use SRv6 SIDs advertised specifically for the given Flex-
Algorithm. Algorithm.
If LFA protection is being used to protect locators associated with a If LFA protection is being used to protect locators associated with a
given Flex-Algorithm, all routers in the area participating in the given Flex-Algorithm, all routers in the area participating in the
given Flex-Algorithm SHOULD advertise at least one Flex-Algorithm given Flex-Algorithm SHOULD advertise at least one Flex-Algorithm-
specific locator and END SID per node and one END.X SID for every specific locator and END SID per node and one END.X SID for every
link that has not been pruned from such Flex-Algorithm computation. link that has not been pruned from such Flex-Algorithm computation.
These locators and SIDs are used to steer traffic over the LFA- These locators and SIDs are used to steer traffic over the LFA-
computed backup path. computed backup path.
14.3. Other Data-planes' Forwarding for Flex-Algorithm 14.3. Other Data Planes' Forwarding for Flex-Algorithm
Any data-plane that wants to use Flex-Algorithm specific forwarding Any data plane that wants to use Flex-Algorithm-specific forwarding
needs to install some form of Flex-Algorithm specific forwarding needs to install some form of Flex-Algorithm-specific forwarding
entries. entries.
Data-plane specific forwarding for Flex-Algorithm MUST be defined for Data-plane-specific forwarding for Flex-Algorithms MUST be defined
each data-plane and is outside the scope of this document. for each data plane and is outside the scope of this document.
15. Operational Considerations 15. Operational Considerations
15.1. Inter-area Considerations 15.1. Inter-area Considerations
The scope of the Flex-Algorithm computation is an area, so is the The scope of the Flex-Algorithm computation and the scope of the FAD
scope of the FAD. In IS-IS, the Router Capability TLV in which the is an area. In IS-IS, the Router Capability TLV in which the FAD
FAD Sub-TLV is advertised MUST have the S-bit clear, which prevents sub-TLV is advertised MUST have the S bit clear, which prevents it
it from being flooded outside the level in which it was originated. from being flooded outside the level in which it was originated.
Even though in OSPF the FAD Sub-TLV can be flooded in an RI LSA that Even though in OSPF the FAD sub-TLV can be flooded in an RI LSA that
has AS flooding scope, the FAD selection is performed for each has an AS flooding scope, the FAD selection is performed for each
individual area in which it is being used. individual area in which it is being used.
There is no requirement for the FAD for a particular Flex-Algorithm There is no requirement for the FAD for a particular Flex-Algorithm
to be identical in all areas in the network. For example, traffic to be identical in all areas in the network. For example, traffic
for the same Flex-Algorithm may be optimized for minimal delay (e.g., for the same Flex-Algorithm may be optimized for minimal delay (e.g.,
using delay metric) in one area or level, while being optimized for using delay metric) in one area or level while being optimized for
available bandwidth (e.g., using IGP metric) in another area or available bandwidth (e.g., using IGP metric) in another area or
level. level.
As described in Section 5.1, IS-IS allows the re-generation of the As described in Section 5.1, IS-IS allows the regeneration of the
winning FAD from level 2, without any modification to it, into a winning FAD from level 2, without any modification to it, into a
level 1 area. This allows the operator to configure the FAD in one level 1 area. This allows the operator to configure the FAD in one
or multiple routers in the level 2, without the need to repeat the or multiple routers in level 2, without the need to repeat the same
same task in each level 1 area, if the intent is to have the same FAD task in each level 1 area, if the intent is to have the same FAD for
for the particular Flex-Algorithm across all levels. This can the particular Flex-Algorithm across all levels. This can similarly
similarly be achieved in OSPF by using the AS flooding scope of the be achieved in OSPF by using the AS flooding scope of the RI LSA in
RI LSA in which the FAD Sub-TLV for the particular Flex-Algoritm is which the FAD sub-TLV for the particular Flex-Algorithm is
advertised. advertised.
Re-generation of the FAD from a level 1 area to the level 2 area is Regeneration of the FAD from a level 1 area to the level 2 area is
not supported in IS-IS, so if the intent is to regenerate the FAD not supported in IS-IS, so if the intent is to regenerate the FAD
between IS-IS levels, the FAD MUST be defined on router(s) that are between IS-IS levels, the FAD MUST be defined on a router(s) that is
in level 2. In OSPF, the FAD definition can be done in any area and in level 2. In OSPF, the FAD definition can be done in any area and
be propagated to all routers in the OSPF routing domain by using the propagated to all routers in the OSPF routing domain by using the AS
AS flooding scope of the RI LSA. flooding scope of the RI LSA.
15.2. Usage of SRLG Exclude Rule with Flex-Algorithm 15.2. Usage of the SRLG Exclude Rule with Flex-Algorithm
There are two different ways in which SRLG information can be used There are two different ways in which SRLG information can be used
with Flex-Algorithm: with Flex-Algorithms:
In a context of a single Flex-Algorithm, it can be used for * In a context of a single Flex-Algorithm, it can be used for
computation of backup paths, as described in computation of backup paths, as described in
[I-D.ietf-rtgwg-segment-routing-ti-lfa]. This usage does not [RTGWG-SEGMENT-ROUTING-TI-LFA]. This usage does not require
require association of any specific SRLG constraint with the given association of any specific SRLG constraint with the given Flex-
Flex-Algorithm definition. Algorithm Definition.
In the context of multiple Flex-Algorithms, it can be used for * In the context of multiple Flex-Algorithms, it can be used for
creating disjoint sets of paths by pruning the links belonging to creating disjoint sets of paths by pruning the links belonging to
a specific SRLG from the topology on which a specific Flex- a specific SRLG from the topology on which a specific Flex-
Algorithm computes its paths. This usage: Algorithm computes its paths. This usage:
Facilitates the usage of already deployed SRLG configurations - facilitates the usage of already deployed SRLG configurations
for setup of disjoint paths between two or more Flex- for the setup of disjoint paths between two or more Flex-
Algorithms. Algorithms and
Requires explicit association of a given Flex-Algorithm with a - requires explicit association of a given Flex-Algorithm with a
specific set of SRLG constraints as defined in Section 6.5 and specific set of SRLG constraints, as defined in Sections 6.5
Section 7.5. and 7.5.
The two usages mentioned above are orthogonal. The two usages mentioned above are orthogonal.
15.3. Max-metric consideration 15.3. Max-Metric Consideration
Both IS-IS and OSPF have a mechanism to set the IGP metric on a link Both IS-IS and OSPF have a mechanism to set the IGP metric on a link
to a value that would make the link either non-reachable or to serve to a value that would make the link either unreachable or serve as
as the link of last resort. Similar functionality would be needed the link of last resort. Similar functionality would be needed for
for the Min Unidirectional Link Delay and TE metric, as these can be the Min Unidirectional Link Delay and TE metric, as these can be used
used to compute Flex-Algorithm paths. to compute Flex-Algorithm paths.
The link can be made un-reachable for all Flex-Algorithms that use The link can be made unreachable for all Flex-Algorithms that use the
Min Unidirectional Link Delay as metric, as described in Section 5.1, Min Unidirectional Link Delay as a metric, as described in
by removing the Flex-Algorithm ASLA Min Unidirectional Link Delay Section 5.1, by removing the Flex-Algorithm ASLA Min Unidirectional
advertisement for the link. The link can be made the link of last Link Delay advertisement for the link. The link can be made the link
resort by setting the delay value in the Flex-Algorithm ASLA delay of last resort by setting the delay value in the Flex-Algorithm ASLA
advertisement for the link to the value of 16,777,215 (2^24 - 1). delay advertisement for the link to the value of 16,777,215 (2^24 -
1).
The link can be made un-reachable for all Flex-Algorithms that use TE The link can be made unreachable for all Flex-Algorithms that use the
metric, as described in Section 5.1, by removing the Flex-Algorithm TE metric, as described in Section 5.1, by removing the Flex-
ASLA TE metric advertisement for the link. The link can be made the Algorithm ASLA TE metric advertisement for the link. The link can be
link of last resort by setting the TE metric value in the Flex- made the link of last resort by setting the TE metric value in the
Algorithm ASLA delay advertisement for the link to the value of (2^24 Flex-Algorithm ASLA delay advertisement for the link to the value of
- 1) in IS-IS and (2^32 - 1) in OSPF. (2^24 - 1) in IS-IS and (2^32 - 1) in OSPF.
15.4. FAD Definition and Changes 15.4. Flexible Algorithm Definition and Changes
When configuring a node to participate in a specific Flex-Algorithm, When configuring a node to participate in a specific Flex-Algorithm,
the components of the FAD (calculation-type, metric-type, the components of the FAD (calculation-type, metric-type, and
constraints) should be considered carefully. The configuration of constraints) should be considered carefully. The configuration of
participation in a particular Flex-Algorithm doesn't guarantee that participation in a particular Flex-Algorithm doesn't guarantee that
the node will actively participate in it, because it may not support the node will actively participate in it, because it may not support
the calculation-type, metric type or some constraint advertised by the calculation-type, the metric-type, or some constraint advertised
the winning FAD (see Section 5.3). Changes in the FAD configuration by the winning FAD (see Section 5.3). Changes in the FAD
should also be considered in light of the capabilities of the configuration should also be considered in light of the capabilities
participating routers in the scope of the FAD advertisement. of the participating routers in the scope of the FAD advertisement.
As Section 5.3 notes, a change in the Flex-Algorithm definition may As Section 5.3 notes, a change in the Flex-Algorithm Definition may
require network-wide SPF re-computation and network re-convergence. require network-wide Shortest Path First (SPF) recomputation and
This potential for disruption should be taken into consideration when network reconvergence. This potential for disruption should be taken
planning and making changes to the FAD. into consideration when planning and making changes to the FAD.
15.5. Number of Flex-Algorithms 15.5. Number of Flex-Algorithms
The maximum number of Flex-Algorithms is determined by the algorithm The maximum number of Flex-Algorithms is determined by the algorithm
range that is (128-255), as specified in Section 4. Although range 128-255, as specified in Section 4. Although possible, it is
possible, it is not expected that all of them will be used not expected that all of them will be used simultaneously.
simultaneously. Typically, only a limited subset of Flex-Algorithms Typically, only a limited subset of Flex-Algorithms is expected to be
is expected to be deployed in the network. deployed in the network.
16. Backward Compatibility 16. Backward Compatibility
This extension brings no new backward compatibility issues. IS-IS, This extension brings no new backward-compatibility issues. IS-IS,
OSPFv2 and OSPFv3 all have well-defined handling of unrecognized TLVs OSPFv2, and OSPFv3 all have well-defined handling of unrecognized
and sub-TLVs that allows the introduction of new extensions, similar TLVs and sub-TLVs that allows the introduction of new extensions,
to those defined here, without introducing any interoperability similar to those defined here, without introducing any
issues. interoperability issues.
17. Security Considerations 17. Security Considerations
This draft adds two new ways to disrupt IGP networks: This document adds two new ways to disrupt IGP networks:
An attacker can hijack a particular Flex-Algorithm by advertising * An attacker can hijack a particular Flex-Algorithm by advertising
a FAD with a priority of 255 (or any priority higher than that of a FAD with a priority of 255 (or any priority higher than that of
the legitimate nodes). the legitimate nodes).
An attacker could make it look like a router supports a particular * An attacker could make it look like a router supports a particular
Flex-Algorithm when it actually doesn't, or vice versa. Flex-Algorithm when it actually doesn't, or vice versa.
Both of these attacks can be addressed by the existing security Both of these attacks can be addressed by the existing security
extensions as described in [RFC5304] and [RFC5310] for IS-IS, in extensions, as described in [RFC5304] and [RFC5310] for IS-IS, in
[RFC2328] and [RFC7474] for OSPFv2, and in [RFC5340] and [RFC4552] [RFC2328] and [RFC7474] for OSPFv2, and in [RFC4552] and [RFC5340]
for OSPFv3. for OSPFv3.
If the node that is authenticated is taken over by an attacker, such If the node that is authenticated is taken over by an attacker, such
rogue node can advertise the FAD for any Flex-Algorithm. Doing so rogue node can advertise the FAD for any Flex-Algorithm. Doing so
may result in traffic for such Flex-Algorithm to be misrouted, or not may result in traffic for such Flex-Algorithm to be misrouted, or not
being delivered at all, for example, by using an unsupported metric- delivered at all, for example, by using an unsupported metric-type,
type, calculation-type, or constraint. Such attack is not calculation-type, or constraint. Such attack is not preventable
preventable through authentication, and it is not different from through authentication, and it is not different from advertising any
advertising any other incorrect information through IS-IS or OSPF. other incorrect information through IS-IS or OSPF.
18. IANA Considerations 18. IANA Considerations
18.1. IGP IANA Considerations 18.1. IGP IANA Considerations
18.1.1. IGP Algorithm Types Registry 18.1.1. IGP Algorithm Types Registry
This document makes the following registrations in the "IGP Algorithm This document makes the following registration in the "IGP Algorithm
Types" registry: Types" registry:
Type: 128-255. +=========+=====================+=====================+
| Value | Description | Reference |
Description: Flexible Algorithms. +=========+=====================+=====================+
| 128-255 | Flexible Algorithms | RFC 9350, Section 4 |
+---------+---------------------+---------------------+
Reference: This document (Section 4). Table 1: IGP Algorithm Types Registry
18.1.2. IGP Metric-Type Registry 18.1.2. IGP Metric-Type Registry
IANA is requested to set up a registry called "IGP Metric-Type IANA has created the "IGP Metric-Type" registry within the "Interior
Registry" under the "Interior Gateway Protocol (IGP) Parameters" IANA Gateway Protocol (IGP) Parameters" registry group. The registration
grouping. The registration policy for this registry is "Standards policy is "Standards Action" [RFC8126] [RFC7120]. Values are
Action" ([RFC8126] and [RFC7120]). assigned from the range 0-255 and have been registered as follows.
Values in this registry come from the range 0-255.
This document registers following values in the "IGP Metric-Type
Registry":
Type: 0
Description: IGP metric
Reference: This document (Section 5.1)
Type: 1
Description: Min Unidirectional Link Delay as defined in
[RFC8570], section 4.2, and [RFC7471], section 4.2.
Reference: This document (Section 5.1)
Type: 2
Description: Traffic Engineering Default Metric as defined in
[RFC5305], section 3.7, and Traffic engineering metric as defined
in [RFC3630], section 2.5.5
Reference: This document (Section 5.1) +======+======================================+===========+
| Type | Description | Reference |
+======+======================================+===========+
| 0 | IGP Metric | RFC 9350, |
| | | Section |
| | | 5.1 |
+------+--------------------------------------+-----------+
| 1 | Min Unidirectional Link Delay as | RFC 9350, |
| | defined in [RFC8570], Section 4.2 | Section |
| | and [RFC7471], Section 4.2 | 5.1 |
+------+--------------------------------------+-----------+
| 2 | Traffic Engineering Default Metric | RFC 9350, |
| | as defined in [RFC5305], Section 3.7 | Section |
| | and Traffic Engineering Metric as | 5.1 |
| | defined in [RFC3630], Section 2.5.5 | |
+------+--------------------------------------+-----------+
18.2. Flexible Algorithm Definition Flags Registry Table 2: IGP Metric-Type Registry
IANA is requested to set up a registry called "IGP Flexible Algorithm 18.2. IGP Flexible Algorithm Definition Flags Registry
Definition Flags Registry" under the "Interior Gateway Protocol (IGP)
Parameters" IANA grouping. The registration policy for this registry
is "Standards Action" ([RFC8126] and [RFC7120]). New registrations
should be assigned in ascending bit order (see Section 6.4).
This document defines the following single bit in Flexible Algorithm IANA has created the "IGP Flexible Algorithm Definition Flags"
Definition Flags registry: registry within the "Interior Gateway Protocol (IGP) Parameters"
registry group. The registration policy is "Standards Action". New
registrations should be assigned in ascending bit order (see
Section 6.4); the following single bit has been assigned as follows.
Bit # Name +=====+=============================+====================+
----- ------------------------------ | Bit | Name | Reference |
0 Prefix Metric Flag (M-flag) +=====+=============================+====================+
| 0 | Prefix Metric Flag (M-flag) | RFC 9350, Sections |
| | | 6.4 and 7.4 |
+-----+-----------------------------+--------------------+
Reference: This document (Section 6.4, Section 7.4). Table 3: IGP Flexible Algorithm Definition Flags Registry
18.3. IS-IS IANA Considerations 18.3. IS-IS IANA Considerations
18.3.1. IS-IS Sub-TLVs for IS-IS Router CAPABILITY TLV 18.3.1. IS-IS Sub-TLVs for IS-IS Router CAPABILITY TLV Registry
This document makes the following registrations in the "IS-IS Sub-
TLVs for IS-IS Router CAPABILITY TLV" registry.
Type: 26. This document makes the following registration in the "IS-IS Sub-TLVs
for IS-IS Router CAPABILITY TLV" registry.
Description: Flexible Algorithm Definition (FAD) +=======+=====================================+=============+
| Value | Description | Reference |
+=======+=====================================+=============+
| 26 | Flexible Algorithm Definition (FAD) | RFC 9350, |
| | | Section 5.1 |
+-------+-------------------------------------+-------------+
Reference: This document (Section 5.1). Table 4: IS-IS Sub-TLVs for IS-IS Router CAPABILITY TLV
Registry
18.3.2. IS-IS Sub-TLVs for TLVs Advertising Prefix Reachability 18.3.2. IS-IS Sub-TLVs for TLVs Advertising Prefix Reachability
Registry
This document makes the following registrations in the "IS-IS Sub- This document makes the following registration in the "IS-IS Sub-TLVs
TLVs for TLVs Advertising Prefix Reachability" registry. for TLVs Advertising Prefix Reachability" registry.
Type: 6
Description: Flexible Algorithm Prefix Metric (FAPM).
Reference: This document (Section 8).
18.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV
This document creates the following Sub-Sub-TLV Registry, under the
IS-IS TLV Codepoints grouping.
Registry: Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV
Registration Procedure: Expert review. (Note that the IS-IS TLV
Codepoints grouping includes Expert Review guidance that applies
to all registries thereunder.)
Reference: This document (Section 5.1)
This document defines the following Sub-Sub-TLVs in the "Sub-Sub-TLVs
for Flexible Algorithm Definition Sub-TLV" registry:
Type: 0
Description: Reserved
Reference: This document.
Type: 1
Description: Flexible Algorithm Exclude Admin Group
Reference: This document (Section 6.1).
Type: 2
Description: Flexible Algorithm Include-Any Admin Group
Reference: This document (Section 6.2).
Type: 3
Description: Flexible Algorithm Include-All Admin Group
Reference: This document (Section 6.3).
Type: 4
Description: Flexible Algorithm Definition Flags
Reference: This document (Section 6.4). +======+==================+====+=====+=====+=====+=====+===========+
| Type | Description | 27 | 135 | 235 | 236 | 237 | Reference |
+======+==================+====+=====+=====+=====+=====+===========+
| 6 | Flexible | n | y | y | y | y | RFC 9350, |
| | Algorithm Prefix | | | | | | Section 8 |
| | Metric (FAPM) | | | | | | |
+------+------------------+----+-----+-----+-----+-----+-----------+
Type: 5 Table 5: IS-IS Sub-TLVs for TLVs Advertising Prefix Reachability
Registry
Description: Flexible Algorithm Exclude SRLG 18.3.3. IS-IS Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV
Registry
Reference: This document (Section 6.5). IANA has created the "IS-IS Sub-Sub-TLVs for Flexible Algorithm
Definition Sub-TLV" registry within the "IS-IS TLV Codepoints"
registry group. The registration procedure is "Expert Review" (note
that the "IS-IS TLV Codepoints" registry group includes Expert Review
guidance that applies to all registries thereunder).
Type: 6-255 The sub-sub-TLVs defined in this document have been assigned as
follows.
Description: Unassigned +=======+========================================+=============+
| Type | Description | Reference |
+=======+========================================+=============+
| 0 | Reserved | RFC 9350 |
+-------+----------------------------------------+-------------+
| 1 | Flexible Algorithm Exclude Admin Group | RFC 9350, |
| | | Section 6.1 |
+-------+----------------------------------------+-------------+
| 2 | Flexible Algorithm Include-Any Admin | RFC 9350, |
| | Group | Section 6.2 |
+-------+----------------------------------------+-------------+
| 3 | Flexible Algorithm Include-All Admin | RFC 9350, |
| | Group | Section 6.3 |
+-------+----------------------------------------+-------------+
| 4 | Flexible Algorithm Definition Flags | RFC 9350, |
| | | Section 6.4 |
+-------+----------------------------------------+-------------+
| 5 | Flexible Algorithm Exclude SRLG | RFC 9350, |
| | | Section 6.5 |
+-------+----------------------------------------+-------------+
| 6-255 | Unassigned | |
+-------+----------------------------------------+-------------+
Reference: This document. Table 6: IS-IS Sub-Sub-TLVs for Flexible Algorithm
Definition Sub-TLV Registry
18.4. OSPF IANA Considerations 18.4. OSPF IANA Considerations
18.4.1. OSPF Router Information (RI) TLVs Registry 18.4.1. OSPF Router Information (RI) TLVs Registry
This specification makes the following registration in the OSPF This document makes the following registration in the "OSPF Router
Router Information (RI) TLVs Registry. Information (RI) TLVs" registry.
Type: 16
Description: Flexible Algorithm Definition (FAD) TLV. +=======+=========================================+=============+
| Value | Description | Reference |
+=======+=========================================+=============+
| 16 | Flexible Algorithm Definition (FAD) TLV | RFC 9350, |
| | | Section 5.2 |
+-------+-----------------------------------------+-------------+
Reference: This document (Section 5.2). Table 7: OSPF Router Information (RI) TLVs Registry
18.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs 18.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs Registry
This document makes the following registrations in the "OSPFv2 This document makes the following registration in the "OSPFv2
Extended Prefix TLV Sub-TLVs" registry. Extended Prefix TLV Sub-TLVs" registry.
Type: 3 +=======+=========================================+===========+
| Value | Description | Reference |
Description: Flexible Algorithm Prefix Metric (FAPM). +=======+=========================================+===========+
| 3 | Flexible Algorithm Prefix Metric (FAPM) | RFC 9350, |
| | | Section 9 |
+-------+-----------------------------------------+-----------+
Reference: This document (Section 9). Table 8: OSPFv2 Extended Prefix TLV Sub-TLVs Registry
18.4.3. OSPFv3 Extended-LSA Sub-TLVs 18.4.3. OSPFv3 Extended-LSA Sub-TLVs Registry
This document makes the following registrations in the "OSPFv3 This document makes the following registrations in the "OSPFv3
Extended-LSA Sub-TLVs" registry. Extended-LSA Sub-TLVs" registry.
Type: 26 +=======+=========================================+==============+
| Value | Description | Reference |
Description: Flexible Algorithm Prefix Metric (FAPM). +=======+=========================================+==============+
| 26 | Flexible Algorithm Prefix Metric (FAPM) | RFC 9350, |
Reference: This document (Section 9). | | | Section 9 |
+-------+-----------------------------------------+--------------+
Type: 33 | 33 | OSPF Flexible Algorithm ASBR Metric | RFC 9350, |
| | | Section 10.2 |
Description: OSPF Flexible Algorithm ASBR Metric +-------+-----------------------------------------+--------------+
Reference: This document (Section 10.2).
For both of these sub-TLVs the column L2BN in the registry is set to
"X" - meaning "sub-TLV is not a Router Link sub-TLV; it MUST NOT
appear in L2 Bundle Member sub-TLV".
18.4.4. OSPF Flex-Algorithm Prefix Metric Bits
This specification requests creation of the "OSPF Flex-Algorithm Table 9: OSPFv3 Extended-LSA Sub-TLVs Registry
Prefix Metric Bits" registry under the "Open Shortest Path First
(OSPF) Parameters" with the following initial values:
Bit Number: 0 18.4.4. OSPF Flex-Algorithm Prefix Metric Bits Registry
Description: E bit - External Type IANA has created the "OSPF Flex-Algorithm Prefix Metric Bits"
registry under the "Open Shortest Path First (OSPF) Parameters"
registry. The registration procedure is "IETF Review". Bits 1-7 are
unassigned, and the initial value has been assigned as follows.
Reference: this document (Section 9). +============+=======================+=====================+
| Bit Number | Description | Reference |
+============+=======================+=====================+
| 0 | E bit - External Type | RFC 9350, Section 9 |
+------------+-----------------------+---------------------+
The bits 1-7 are unassigned and the registration procedure to be Table 10: OSPF Flex-Algorithm Prefix Metric Bits Registry
followed for this registry is IETF Review.
18.4.5. OSPFv2 Opaque LSA Option Types 18.4.5. Opaque Link-State Advertisements (LSA) Option Types Registry
This document makes the following registrations in the "Opaque Link- This document makes the following registration in the "Opaque Link-
State Advertisements (LSA) Option Types" registry under the "Open State Advertisements (LSA) Option Types" registry within the "Open
Shortest Path First (OSPF) Opaque Link-State Advertisements (LSA) Shortest Path First (OSPF) Opaque Link-State Advertisements (LSA)
Option Types" grouping. Option Types" registry group.
Value: 11
Description: OSPFv2 Extended Inter-Area ASBR (EIA-ASBR) LSA
Reference: This document (Section 10.1).
18.4.6. OSPFv2 Extended Inter-Area ASBR TLVs
This specification requests creation of "OSPFv2 Extended Inter-Area
ASBR TLVs" registry under the OSPFv2 Parameters Registry with the
following initial values.
Value: 1
Description : Extended Inter-Area ASBR +=======+==========================+==============+
| Value | Opaque Type | Reference |
+=======+==========================+==============+
| 11 | OSPFv2 Extended Inter- | RFC 9350, |
| | Area ASBR (EIA-ASBR) LSA | Section 10.1 |
+-------+--------------------------+--------------+
Reference: this document Table 11: Opaque Link-State Advertisements
(LSA) Option Types Registry
The values 2 to 32767 are unassigned, values 32768 to 33023 are 18.4.6. OSPFv2 Extended Inter-Area ASBR TLVs Registry
reserved for experimental use while the values 0 and 33024 to 65535
are reserved. The registration procedure to be followed for this
registry is IETF Review or IESG Approval.
18.4.7. OSPFv2 Inter-Area ASBR Sub-TLVs IANA has created the "OSPFv2 Extended Inter-Area ASBR TLVs" registry
within the "Open Shortest Path First v2 (OSPFv2) Parameters" registry
group. The registration procedure is "IETF Review" or "IESG
Approval". The initial value has been assigned as follows.
This specification requests creation of "OSPFv2 Extended Inter-Area +=======+==========================+===========+
ASBR Sub-TLVs" registry under the "Open Shortest Path First v2 | Value | Description | Reference |
(OSPFv2) Parameters" grouping, with the following initial values. +=======+==========================+===========+
| 1 | Extended Inter-Area ASBR | RFC 9350 |
+-------+--------------------------+-----------+
Value: 1 Table 12: OSPFv2 Extended Inter-Area ASBR
TLVs Registry
Description : OSPF Flexible Algorithm ASBR Metric The values 2-32767 are unassigned, the values 32768-33023 are
reserved for Experimental Use, and the values 0 and 33024-65535 are
reserved.
Reference: this document 18.4.7. OSPFv2 Extended Inter-Area ASBR Sub-TLVs Registry
The values 2 to 32767 are unassigned, values 32768 to 33023 are IANA has created the "OSPFv2 Extended Inter-Area ASBR Sub-TLVs"
reserved for experimental use while the values 0 and 33024 to 65535 registry under the "Open Shortest Path First v2 (OSPFv2) Parameters"
are reserved. The registration procedure to be followed for this registry. The registration procedure is "IETF Review" or "IESG
registry is IETF Review or IESG Approval. Approval". The initial value has been assigned as follows.
18.4.8. OSPF Flexible Algorithm Definition TLV Sub-TLV Registry +=======+=====================================+===========+
| Value | Description | Reference |
+=======+=====================================+===========+
| 1 | OSPF Flexible Algorithm ASBR Metric | RFC 9350 |
+-------+-------------------------------------+-----------+
This document creates the following registry under the "Open Shortest Table 13: OSPFv2 Extended Inter-Area ASBR Sub-TLVs Registry
Path First (OSPF) Parameters" grouping:
Registry: OSPF Flexible Algorithm Definition TLV sub-TLVs The values 2-32767 are unassigned, the values 32768-33023 are
reserved for Experimental Use, and the values 0 and 33024-65535 are
reserved.
Registration Procedure: IETF Review or IESG Approval 18.4.8. OSPF Flexible Algorithm Definition TLV Sub-TLVs Registry
Reference: This document (Section 5.2) IANA has created the "OSPF Flexible Algorithm Definition TLV Sub-
TLVs" registry within the "Open Shortest Path First (OSPF)
Parameters" registry group. The registration procedure is "IETF
Review" or "IESG Approval".
The "OSPF Flexible Algorithm Definition TLV sub-TLV" registry will The "OSPF Flexible Algorithm Definition TLV Sub-TLVs" registry will
define sub-TLVs at any level of nesting for the Flexible Algorithm define sub-TLVs at any level of nesting for the Flexible Algorithm
TLV New values can be allocated via IETF Review or IESG Approval. TLV, and new values can be allocated via the registration procedure.
This document registers following Sub-TLVs in the "OSPF Flexible
Algorithm Definition TLV sub-TLV" registry:
Type: 0
Description: Reserved
Reference: This document (Section 7.1).
Type: 1
Description: Flexible Algorithm Exclude Admin Group
Reference: This document (Section 7.1).
Type: 2
Description: Flexible Algorithm Include-Any Admin Group
Reference: This document (Section 7.2).
Type: 3
Description: Flexible Algorithm Include-All Admin Group
Reference: This document (Section 7.3).
Type: 4
Description: Flexible Algorithm Definition Flags
Reference: This document (Section 7.4).
Type: 5 This document registers the following sub-TLVs.
Description: Flexible Algorithm Exclude SRLG +============+========================================+=============+
| Bit Number | Description | Reference |
+============+========================================+=============+
| 0 | Reserved | RFC 9350 |
+------------+----------------------------------------+-------------+
| 1 | Flexible Algorithm | RFC 9350, |
| | Exclude Admin Group | Section 7.1 |
+------------+----------------------------------------+-------------+
| 2 | Flexible Algorithm | RFC 9350, |
| | Include-Any Admin Group | Section 7.2 |
+------------+----------------------------------------+-------------+
| 3 | Flexible Algorithm | RFC 9350, |
| | Include-All Admin Group | Section 7.3 |
+------------+----------------------------------------+-------------+
| 4 | Flexible Algorithm | RFC 9350, |
| | Definition Flags | Section 7.4 |
+------------+----------------------------------------+-------------+
| 5 | Flexible Algorithm | RFC 9350, |
| | Exclude SRLG | Section 7.5 |
+------------+----------------------------------------+-------------+
Reference: This document (Section 7.5). Table 14: OSPF Flexible Algorithm Definition TLV Sub-TLVs Registry
The values 6 to 32767 are unassigned, values 32768-33023 are for The values 6-32767 are unassigned, and values 32768-33023 are for
experimental use; these will not be registered with IANA. Experimental Use; these will not be registered with IANA.
Types in the range 33024-65535 are not to be assigned at this time. Types in the range 33024-65535 are not to be assigned at this time.
Before any assignments can be made in the 33024-65535 range, there Before any assignments can be made in the 33024-65535 range, there
MUST be an IETF specification that specifies IANA Considerations that MUST be an IETF specification that specifies IANA considerations that
covers the range being assigned. cover the range being assigned.
18.4.9. Link Attribute Applications Registry
This document registers following bit in the Link Attribute
Applications Registry:
Bit-3
Description: Flexible Algorithm (X-bit)
Reference: This document (Section 12).
19. Acknowledgements
This draft, among other things, is also addressing the problem that
the [I-D.gulkohegde-routing-planes-using-sr] was trying to solve.
All authors of that draft agreed to join this draft.
Thanks to Eric Rosen, Tony Przygienda, William Britto A J, Gunter Van
De Velde, Dirk Goethals, Manju Sivaji and, Baalajee S for their
detailed review and excellent comments.
Thanks to Cengiz Halit for his review and feedback during initial 18.4.9. Link Attribute Application Identifiers Registry
phase of the solution definition.
Thanks to Kenji Kumaki for his comments. This document registers the following bit in the "Link Attribute
Application Identifiers" registry.
Thanks to Acee Lindem for editorial comments. +=====+============================+======================+
| Bit | Description | Reference |
+=====+============================+======================+
| 3 | Flexible Algorithm (X-bit) | RFC 9350, Section 12 |
+-----+----------------------------+----------------------+
20. References Table 15: Link Attribute Application Identifiers Registry
20.1. Normative References 19. References
[I-D.ietf-lsr-isis-srv6-extensions] 19.1. Normative References
Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
Z. Hu, "IS-IS Extensions to Support Segment Routing over
IPv6 Dataplane", Work in Progress, Internet-Draft, draft-
ietf-lsr-isis-srv6-extensions-18, 20 October 2021,
<https://www.ietf.org/archive/id/draft-ietf-lsr-isis-srv6-
extensions-18.txt>.
[ISO10589] ISO, "Intermediate system to Intermediate system intra- [ISO10589] ISO, "Information technology - Telecommunications and
domain routeing information exchange protocol for use in information exchange between systems - Intermediate System
conjunction with the protocol for providing the to Intermediate System intra-domain routeing information
connectionless-mode Network Service (ISO 8473)", ISO/ exchange protocol for use in conjunction with the protocol
IEC 10589:2002, Second Edition, November 2002. for providing the connectionless-mode network service (ISO
8473)", Second Edition, ISO/IEC 10589:2002, November 2002.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in [RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in
Support of Generalized Multi-Protocol Label Switching Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005, (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,
<https://www.rfc-editor.org/info/rfc4203>. <https://www.rfc-editor.org/info/rfc4203>.
skipping to change at page 48, line 37 skipping to change at line 2174
[RFC8919] Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and [RFC8919] Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and
J. Drake, "IS-IS Application-Specific Link Attributes", J. Drake, "IS-IS Application-Specific Link Attributes",
RFC 8919, DOI 10.17487/RFC8919, October 2020, RFC 8919, DOI 10.17487/RFC8919, October 2020,
<https://www.rfc-editor.org/info/rfc8919>. <https://www.rfc-editor.org/info/rfc8919>.
[RFC8920] Psenak, P., Ed., Ginsberg, L., Henderickx, W., Tantsura, [RFC8920] Psenak, P., Ed., Ginsberg, L., Henderickx, W., Tantsura,
J., and J. Drake, "OSPF Application-Specific Link J., and J. Drake, "OSPF Application-Specific Link
Attributes", RFC 8920, DOI 10.17487/RFC8920, October 2020, Attributes", RFC 8920, DOI 10.17487/RFC8920, October 2020,
<https://www.rfc-editor.org/info/rfc8920>. <https://www.rfc-editor.org/info/rfc8920>.
20.2. Informative References [RFC9352] Psenak, P., Ed., Filsfils, C., Bashandy, A., Decraene, B.,
and Z. Hu, "IS-IS Extensions to Support Segment Routing
[I-D.gulkohegde-routing-planes-using-sr] over the IPv6 Data Plane", RFC 9352, DOI 10.17487/RFC9352,
Hegde, S. and A. Gulko, "Separating Routing Planes using February 2023, <https://www.rfc-editor.org/info/rfc9352>.
Segment Routing", Work in Progress, Internet-Draft, draft-
gulkohegde-routing-planes-using-sr-00, 13 March 2017,
<https://www.ietf.org/archive/id/draft-gulkohegde-routing-
planes-using-sr-00.txt>.
[I-D.ietf-rtgwg-segment-routing-ti-lfa] 19.2. Informative References
Litkowski, S., Bashandy, A., Filsfils, C., Francois, P.,
Decraene, B., and D. Voyer, "Topology Independent Fast
Reroute using Segment Routing", Work in Progress,
Internet-Draft, draft-ietf-rtgwg-segment-routing-ti-lfa-
08, 21 January 2022, <https://www.ietf.org/archive/id/
draft-ietf-rtgwg-segment-routing-ti-lfa-08.txt>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998, DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>. <https://www.rfc-editor.org/info/rfc2328>.
[RFC3101] Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option", [RFC3101] Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option",
RFC 3101, DOI 10.17487/RFC3101, January 2003, RFC 3101, DOI 10.17487/RFC3101, January 2003,
<https://www.rfc-editor.org/info/rfc3101>. <https://www.rfc-editor.org/info/rfc3101>.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering [RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
skipping to change at page 50, line 31 skipping to change at line 2256
D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE) D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE)
Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March
2019, <https://www.rfc-editor.org/info/rfc8570>. 2019, <https://www.rfc-editor.org/info/rfc8570>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer, [RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6 D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986, (SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021, DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>. <https://www.rfc-editor.org/info/rfc8986>.
[ROUTING-PLANES-USING-SR]
Hegde, S. and A. Gulko, "Separating Routing Planes using
Segment Routing", Work in Progress, Internet-Draft, draft-
gulkohegde-routing-planes-using-sr-00, 13 March 2017,
<https://datatracker.ietf.org/doc/html/draft-gulkohegde-
routing-planes-using-sr-00>.
[RTGWG-SEGMENT-ROUTING-TI-LFA]
Litkowski, S., Bashandy, A., Filsfils, C., Francois, P.,
Decraene, B., and D. Voyer, "Topology Independent Fast
Reroute using Segment Routing", Work in Progress,
Internet-Draft, draft-ietf-rtgwg-segment-routing-ti-lfa-
09, 23 December 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-rtgwg-
segment-routing-ti-lfa-09>.
Acknowledgements
This document, among other things, addresses the problem that
[ROUTING-PLANES-USING-SR] was trying to solve. All authors of that
document agreed to join this document.
Thanks to Eric Rosen, Tony Przygienda, William Britto A. J., Gunter
Van de Velde, Dirk Goethals, Manju Sivaji, and Baalajee S. for their
detailed review and excellent comments.
Thanks to Cengiz Halit for his review and feedback during the initial
phase of the solution definition.
Thanks to Kenji Kumaki for his comments.
Thanks to Acee Lindem for editorial comments.
Authors' Addresses Authors' Addresses
Peter Psenak (editor) Peter Psenak (editor)
Cisco Systems, Inc. Cisco Systems, Inc.
Apollo Business Center Apollo Business Center
Mlynske nivy 43 Mlynske nivy 43
Bratislava 82109 Bratislava
Slovakia Slovakia
Email: ppsenak@cisco.com Email: ppsenak@cisco.com
Shraddha Hegde Shraddha Hegde
Juniper Networks, Inc. Juniper Networks, Inc.
Embassy Business Park Embassy Business Park
Bangalore, KA Bangalore 560093
560093 KA
India India
Email: shraddha@juniper.net Email: shraddha@juniper.net
Clarence Filsfils Clarence Filsfils
Cisco Systems, Inc. Cisco Systems, Inc.
Brussels Brussels
Belgium Belgium
Email: cfilsfil@cisco.com Email: cfilsfil@cisco.com
Ketan Talaulikar Ketan Talaulikar
Cisco Systems, Inc Cisco Systems, Inc
India India
Email: ketant.ietf@gmail.com Email: ketant.ietf@gmail.com
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