Internet Engineering Task Force (IETF) D. Dhody
Request for Comments: 9168 Huawei Technologies
Category: Standards Track A. Farrel
ISSN: 2070-1721 Old Dog Consulting
Z. Li
Huawei Technologies
December 2021
January 2022
Path Computation Element Communication Protocol (PCEP) Extension for
Flow Specification
Abstract
The Path Computation Element (PCE) is a functional component capable
of selecting paths through a traffic engineering (TE) network. These
paths may be supplied in response to requests for computation or may
be unsolicited requests issued by the PCE to network elements. Both
approaches use the PCE Communication Protocol (PCEP) to convey the
details of the computed path.
Traffic flows may be categorized and described using "Flow
Specifications". RFC 8955 defines the Flow Specification and
describes how Flow Specification components are used to describe
traffic flows. RFC 8955 also defines how Flow Specifications may be
distributed in BGP to allow specific traffic flows to be associated
with routes.
This document specifies a set of extensions to PCEP to support
dissemination of Flow Specifications. This allows a PCE to indicate
what traffic should be placed on each path that it is aware of.
The extensions defined in this document include the creation, update,
and withdrawal of Flow Specifications via PCEP and can be applied to
tunnels initiated by the PCE or to tunnels where control is delegated
to the PCE by the Path Computation Client (PCC). Furthermore, a PCC
requesting a new path can include Flow Specifications in the request
to indicate the purpose of the tunnel allowing the PCE to factor this
into the path computation.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
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/rfc9168.
Copyright Notice
Copyright (c) 2021 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
include Revised BSD License text as described in Section 4.e of the
Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.
Table of Contents
1. Introduction
2. Terminology
3. Procedures for PCE Use of Flow Specifications
3.1. Context for PCE Use of Flow Specifications
3.2. Elements of the Procedure
3.2.1. Capability Advertisement
3.2.1.1. PCEP OPEN Open Message
3.2.1.2. IGP PCE Capabilities Advertisement
3.2.2. Dissemination Procedures
3.2.3. Flow Specification Synchronization
4. PCE FlowSpec Capability TLV
5. PCEP FLOWSPEC Object
6. Flow Filter TLV
7. Flow Specification TLVs
8. Detailed Procedures
8.1. Default Behavior and Backward Compatibility
8.2. Composite Flow Specifications
8.3. Modifying Flow Specifications
8.4. Multiple Flow Specifications
8.5. Adding and Removing Flow Specifications
8.6. VPN Identifiers
8.7. Priorities and Overlapping Flow Specifications
9. PCEP Messages
10. IANA Considerations
10.1. PCEP Objects
10.1.1. PCEP FLOWSPEC Object Flag Field
10.2. PCEP TLV Type Indicators
10.3. Flow Specification TLV Type Indicators
10.4. PCEP Error Codes
10.5. PCE Capability Flag
11. Security Considerations
12. Manageability Considerations
12.1. Management of Multiple Flow Specifications
12.2. Control of Function through Configuration and Policy
12.3. Information and Data Models
12.4. Liveness Detection and Monitoring
12.5. Verifying Correct Operation
12.6. Requirements for Other Protocols and Functional Components
12.7. Impact on Network Operation
13. References
13.1. Normative References
13.2. Informative References
Acknowledgements
Contributors
Authors' Addresses
1. Introduction
[RFC4655] defines the Path Computation Element (PCE), a functional
component capable of computing paths for use in traffic engineering
networks. PCE was originally conceived for use in Multiprotocol
Label Switching (MPLS) for traffic engineering (TE) networks to
derive the routes of Label Switched Paths (LSPs). However, the scope
of PCE was quickly extended to make it applicable to networks
controlled by Generalized MPLS (GMPLS), and more recent work has
brought other traffic engineering technologies and planning
applications into scope (for example, Segment Routing (SR)
[RFC8664]).
[RFC5440] describes the PCEP. PCE Communication Protocol (PCEP). PCEP
defines the communication between a Path Computation Client (PCC) and
a PCE, or between PCE and PCE, enabling computation of the path for
MPLS-TE LSPs.
Stateful PCE [RFC8231] specifies a set of extensions to PCEP to
enable control of TE-LSPs by a PCE that retains state about the LSPs
provisioned in the network (a stateful PCE). [RFC8281] describes the
setup, maintenance, and teardown of LSPs initiated by a stateful PCE
without the need for local configuration on the PCC, thus allowing
for a dynamic network that is centrally controlled. [RFC8283]
introduces the architecture for PCE as a central controller and
describes how PCE can be viewed as a component that performs
computation to place "flows" within the network and decide how these
flows are routed.
The description of traffic flows by the combination of multiple Flow
Specification components and their dissemination as traffic flow
specifications (Flow Specifications) is described for BGP in
[RFC8955]. In BGP, a Flow Specification is comprised of traffic
filtering rules and is associated with actions to perform on the
packets that match the Flow Specification. The BGP routers that
receive a Flow Specification can classify received packets according
to the traffic filtering rules and can direct packets based on the
associated actions.
When a PCE is used to initiate tunnels (such as TE-LSPs or SR paths)
using PCEP, it is important that the head end of the tunnels
understands what traffic to place on each tunnel. The data flows
intended for a tunnel can be described using Flow Specification
components. When PCEP is in use for tunnel initiation, it makes
sense for that same protocol to be used to distribute the Flow
Specification components that describe what data is to flow on those
tunnels.
This document specifies a set of extensions to PCEP to support
dissemination of Flow Specification components. We term the
description of a traffic flow using Flow Specification components as
a "Flow Specification". This term is conceptually the same as the
term used in [RFC8955]; however, no mechanism is provided to
distribute an action associated with the Flow Specification because
there is only one action that is applicable in the PCEP context (that
is, directing the matching traffic to the identified LSP).
The extensions defined in this document include the creation, update,
and withdrawal of Flow Specifications via PCEP and can be applied to
tunnels initiated by the PCE or to tunnels where control is delegated
to the PCE by the PCC. Furthermore, a PCC requesting a new path can
include Flow Specifications in the request to indicate the purpose of
the tunnel allowing the PCE to factor this into the path computation.
Flow Specifications are carried in TLVs within a new object called
the FLOWSPEC object defined in this document. The flow filtering
rules indicated by the Flow Specifications are mainly defined by BGP
Flow Specifications.
Note that PCEP-installed Flow Specifications are intended to be
installed only at the head end of the LSP to which they direct
traffic. It is acceptable (and potentially desirable) that other
routers in the network have Flow Specifications installed that match
the same traffic but direct it onto different routes or to different
LSPs. Those other Flow Specifications may be installed using the
PCEP extensions defined in this document, distributed using BGP per
[RFC8955], or configured using manual operations. Since this
document is about PCEP-installed Flow Specifications, those other
Flow Specifications at other routers are out of scope. In this
context, however, it is worth noting that changes to the wider
routing system (such as the distribution and installation of BGP Flow
Specifications, or fluctuations in the IGP link state database) might
mean that traffic matching the PCEP Flow Specification never reaches
the head end of the LSP at which the PCEP Flow Specification has been
installed. This may or may not be desirable according to the
operator's traffic engineering and routing policies and is
particularly applicable at LSPs that do not have their head ends at
the ingress edge of the network, but it is not an effect that this
document seeks to address.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document uses the following terms defined in [RFC5440]: PCC,
PCE, and PCEP Peer.
The following term from [RFC8955] is used frequently throughout this
document:
| A Flow Specification is an n-tuple consisting of several matching
| criteria that can be applied to IP traffic. A given IP packet is
| said to match the defined Flow Specification if it matches all the
| specified criteria.
[RFC8955] also states that "[a] given Flow Specification may be
associated with a set of attributes" and that "...attributes can be
used to encode a set of predetermined actions." However, in the
context of this document, no action is explicitly specified as
associated with the Flow Specification since the action "forward of forwarding
all matching traffic onto the associated path" path is implicit.
How an implementation decides to filter traffic that matches a Flow
Specification does not form part of this specification, but a flag is
provided to indicate whether the sender of a PCEP message that
includes a Flow Specification intends it to be installed as a Longest
Prefix Match (LPM) route or as a Flow Specification policy.
This document uses the terms "stateful PCE" and "active PCE" as
advocated in [RFC7399].
3. Procedures for PCE Use of Flow Specifications
3.1. Context for PCE Use of Flow Specifications
In the PCE architecture, there are five steps in the setup and use of
LSPs:
1. Decide which LSPs to set up. The decision may be made by a user,
by a PCC, or by the PCE. There can be a number of triggers for
this, including user intervention and dynamic response to changes
in traffic demands.
2. Decide what properties to assign to an LSP. This can include
bandwidth reservations, priorities, and the Differentiated
Services Code Point (DSCP) (i.e., MPLS Traffic Class field).
This function is also determined by user configuration or in
response to predicted or observed traffic demands.
3. Decide what traffic to put on the LSP. This is effectively
determining which traffic flows to assign to which LSPs;
practically, this is closely linked to the first two decisions
listed above.
4. Cause the LSP to be set up and modified to have the right
characteristics. This will usually involve the PCE advising or
instructing the PCC at the head end of the LSP, and the PCC will
then signal the LSP across the network.
5. Tell the head end of the LSP what traffic to put on the LSP.
This may happen after or at the same time as the LSP is set up.
This step is the subject of this document.
3.2. Elements of the Procedure
There are three elements in the procedure:
1. A PCE and a PCC must be able to indicate whether or not they
support the use of Flow Specifications.
2. A PCE or PCC must be able to include Flow Specifications in PCEP
messages with a clear understanding of the applicability of those
Flow Specifications in each case. This includes whether the use
of such information is mandatory, constrained, or optional and
how overlapping Flow Specifications will be resolved.
3. Flow Specification information/state must be synchronized between
PCEP peers so that, on recovery, the peers have the same
understanding of which Flow Specifications apply just as is
required in the case of stateful PCE and LSP delegation (see
Section 5.6 of [RFC8231]).
The following subsections describe these points.
3.2.1. Capability Advertisement
As with most PCEP capability advertisements, the ability to support
Flow Specifications can be indicated in the PCEP OPEN Open message or in
IGP PCE capability advertisements.
3.2.1.1. PCEP OPEN Open Message
During PCEP session establishment, a PCC or PCE that supports the
procedures described in this document announces this fact by
including the "PCE PCE FlowSpec Capability" Capability TLV (described in Section 4) in
the OPEN object carried in the PCEP OPEN Open message.
The presence of the PCE FlowSpec Capability TLV in the OPEN object in
a PCE's OPEN Open message indicates that the PCE can distribute FlowSpecs
to PCCs and can receive FlowSpecs in messages from PCCs.
The presence of the PCE FlowSpec Capability TLV in the OPEN object in
a PCC's OPEN Open message indicates that the PCC supports the FlowSpec
functionality described in this document.
If either one of a pair of PCEP peers does not include the PCE
FlowSpec Capability TLV in the OPEN object in its OPEN Open message, then
the other peer MUST NOT include a FLOWSPEC object in any PCEP message
sent to the peer. If a FLOWSPEC object is received when support has
not been indicated, the receiver will respond with a PCErr message
reporting the objects containing the FlowSpec as described in
[RFC5440]: that is, it will use "Unknown Object" if it does not
support this specification and "Not supported object" if it supports
this specification but has not chosen to support FLOWSPEC objects on
this PCEP session.
3.2.1.2. IGP PCE Capabilities Advertisement
The ability to advertise support for PCEP and PCE features in IGP
advertisements is provided for OSPF in [RFC5088] and for IS-IS in
[RFC5089]. The mechanism uses the PCE Discovery TLV, which has a
PCE-CAP-FLAGS sub-TLV containing bit flags, each of which indicates
support for a different feature.
This document defines a new PCE-CAP-FLAGS sub-TLV bit, the FlowSpec
Capable flag (bit number 16). Setting the bit indicates that an
advertising PCE supports the procedures defined in this document.
Note that while PCE FlowSpec capability may be advertised during
discovery, PCEP speakers that wish to use Flow Specification in PCEP
MUST negotiate PCE FlowSpec capability during PCEP session setup, as
specified in Section 3.2.1.1. A PCC MAY initiate PCE FlowSpec
capability negotiation at PCEP session setup even if it did not
receive any IGP PCE capability advertisement, and a PCEP peer that
advertised support for FlowSpec in the IGP is not obliged to support
these procedures on any given PCEP session.
3.2.2. Dissemination Procedures
This section describes the procedures to support Flow Specifications
in PCEP messages.
The primary purpose of distributing Flow Specification information is
to allow a PCE to indicate to a PCC what traffic it should place on a
path (such as an LSP or an SR path). This means that the Flow
Specification may be included in:
* PCInitiate messages so that an active PCE can indicate the traffic
to place on a path at the time that the PCE instantiates the path.
* PCUpd messages so that an active PCE can indicate or change the
traffic to place on a path that has already been set up.
* PCRpt messages so that a PCC can report the traffic that the PCC
will place on the path.
* PCReq messages so that a PCC can indicate what traffic it plans to
place on a path when it requests that the PCE perform a
computation in case that information aids the PCE in its work.
* PCRep messages so that a PCE that has been asked to compute a path
can suggest which traffic could be placed on a path that a PCC may
be about to set up.
* PCErr messages so that issues related to paths and the traffic
they carry can be reported to the PCE by the PCC and problems with
other PCEP messages that carry Flow Specifications can be
reported.
To carry Flow Specifications in PCEP messages, this document defines
a new PCEP object called the "PCEP FLOWSPEC object". The object is
OPTIONAL in the messages described above and MAY appear more than
once in each message.
To describe a traffic flow, the PCEP FLOWSPEC object carries a Flow
Filter TLV.
The inclusion of multiple PCEP FLOWSPEC objects allows multiple
traffic flows to be placed on a single path.
Once a PCE and PCC have established that they can both support the
use of Flow Specifications in PCEP messages, such information may be
exchanged at any time for new or existing paths.
The application and prioritization of Flow Specifications are
described in Section 8.7.
As per [RFC8231], any attributes of the path received from a PCE are
subject to the PCC's local policy. This holds true for the Flow
Specifications as well.
3.2.3. Flow Specification Synchronization
The Flow Specifications are carried along with the LSP state
information as per [RFC8231], making the Flow Specifications part of
the LSP database (LSP-DB). Thus, the synchronization of the Flow
Specification information is done as part of LSP-DB synchronization.
This may be achieved using normal state synchronization procedures as
described in [RFC8231] or enhanced state synchronization procedures
as defined in [RFC8232].
The approach selected will be implementation and deployment specific
and will depend on issues such as how the databases are constructed
and what level of synchronization support is needed.
4. PCE FlowSpec Capability TLV
The PCE-FLOWSPEC-CAPABILITY TLV is an optional TLV that can be
carried in the OPEN object [RFC5440] to exchange the PCE FlowSpec
capabilities of the PCEP speakers.
The format of the PCE-FLOWSPEC-CAPABILITY TLV follows the format of
all PCEP TLVs as defined in [RFC5440] and is shown in Figure 1.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=51 | Length=2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value=0 | Padding |
+---------------------------------------------------------------+
Figure 1: PCE-FLOWSPEC-CAPABILITY TLV Format
The type of the PCE-FLOWSPEC-CAPABILITY TLV is 51, and it has a fixed
length of 2 octets. The Value field MUST be set to 0 and MUST be
ignored on receipt. The two bytes of padding MUST be set to zero and
ignored on receipt.
The inclusion of this TLV in an OPEN object indicates that the sender
can perform FlowSpec handling as defined in this document.
5. PCEP FLOWSPEC Object
The PCEP FLOWSPEC object defined in this document is compliant with
the PCEP object format defined in [RFC5440]. It is OPTIONAL in the
PCReq, PCRep, PCErr, PCInitiate, PCRpt, and PCUpd messages and MAY be
present zero, one, or more times. Each instance of the object
specifies a separate traffic flow.
The PCEP FLOWSPEC object MAY carry a FlowSpec filter rule encoded in
a Flow Filter TLV as defined in Section 6.
The FLOWSPEC Object-Class is 43 (to be assigned by IANA).
The FLOWSPEC Object-Type is 1.
The format of the body of the PCEP FLOWSPEC object is shown in
Figure 2.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FS-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFI | Reserved | Flags |L|R|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: PCEP FLOWSPEC Object Body Format
FS-ID (32 bits): A PCEP-specific identifier for the FlowSpec
information. A PCE or PCC creates an FS-ID for each FlowSpec that
it originates, and the value is unique within the scope of that
PCE or PCC and is constant for the lifetime of a PCEP session.
All subsequent PCEP messages can identify the FlowSpec using the
FS-ID. The values 0 and 0xFFFFFFFF are reserved and MUST NOT be
used. Note that [NUMERIC-IDS-SEC] gives advice on assigning
transient numeric identifiers such as the FS-ID so as to minimize
security risks.
AFI (16 bits): Address Family Identifier as used in BGP [RFC4760]
(AFI=1 for IPv4 or VPNv4, AFI=2 for IPv6 and VPNv6 as per
[RFC8956]).
Reserved (8 bits): MUST be set to zero on transmission and ignored
on receipt.
Flags (8 bits): Two flags are currently assigned:
R bit: The Remove bit is set when a PCEP FLOWSPEC object is
included in a PCEP message to indicate removal of the Flow
Specification from the associated tunnel. If the bit is clear,
the Flow Specification is being added or modified.
L bit: The Longest Prefix Match (LPM) bit is set to indicate that
the Flow Specification is to be installed as a route subject to
LPM forwarding. If the bit is clear, the Flow Specification
described by the Flow Filter TLV (see Section 6) is to be
installed as a Flow Specification. If the bit is set, only
Flow Specifications that describe IPv4 or IPv6 destinations are
meaningful in the Flow Filter TLV, and others are ignored. If
the L is set and the receiver does not support the use of Flow
Specifications that are present in the Flow Filter TLV for the
installation of a route subject to LPM forwarding, then the
PCEP peer MUST respond with a PCErr message with Error-Type 30
(FlowSpec Error) and Error-value 5 (Unsupported LPM Route).
Unassigned bits MUST be set to zero on transmission and ignored on
receipt.
If the PCEP speaker receives a message with the R bit set in the
FLOWSPEC object and the Flow Specification identified with an FS-ID
does not exist, it MUST generate a PCErr with Error-Type 30 (FlowSpec
Error) and Error-value 4 (Unknown FlowSpec).
If the PCEP speaker does not understand or support the AFI in the
FLOWSPEC message, the PCEP peer MUST respond with a PCErr message
with Error-Type 30 (FlowSpec Error) and Error-value 2 (Malformed
FlowSpec).
The following TLVs can be used in the FLOWSPEC object:
Speaker Entity Identifier TLV: As specified in [RFC8232], the
SPEAKER-ENTITY-ID TLV encodes a unique identifier for the node
that does not change during the lifetime of the PCEP speaker.
This is used to uniquely identify the FlowSpec originator and thus
is used in conjunction with the FS-ID to uniquely identify the
FlowSpec information. This TLV MUST be included. If the TLV is
missing, the PCEP peer MUST respond with a PCErr message with
Error-Type 30 (FlowSpec Error) and Error-value 2 (Malformed
FlowSpec). If more than one instance of this TLV is present, the
first MUST be processed, and subsequent instances MUST be ignored.
Flow Filter TLV (variable): One TLV MAY be included. The Flow
Filter TLV is OPTIONAL when the R bit is set.
The Flow Filter TLV MUST be present when the R bit is clear. If the
TLV is missing when the R bit is clear, the PCEP peer MUST respond
with a PCErr message with Error-Type 30 (FlowSpec Error) and Error-
value 2 (Malformed FlowSpec).
Filtering based on the L2 fields is out of scope of this document.
6. Flow Filter TLV
One new PCEP TLV is defined to convey Flow Specification filtering
rules that specify what traffic is carried on a path. The TLV
follows the format of all PCEP TLVs as defined in [RFC5440]. The
Type field values come from the code point space for PCEP TLVs and
has the value 52 for Flow Filter TLV.
The Value field of the TLV contains one or more sub-TLVs (the Flow
Specification TLVs) as defined in Section 7, and they represent the
complete definition of a Flow Specification for traffic to be placed
on the tunnel. This tunnel is indicated by the PCEP message in which
the PCEP FLOWSPEC object is carried. The set of Flow Specification
TLVs in a single instance of a Flow Filter TLV is combined to
indicate the specific Flow Specification. Note that the PCEP
FLOWSPEC object can include just one Flow Filter TLV.
Further Flow Specifications can be included in a PCEP message by
including additional FLOWSPEC objects.
In the future, there may be a desire to add support for L2 Flow
Specifications (such as described in [BGP-L2VPN]).
7. Flow Specification TLVs
The Flow Filter TLV carries one or more Flow Specification TLVs. The
Flow Specification TLV follows the format of all PCEP TLVs as defined
in [RFC5440]. However, the Type values are selected from a separate
IANA registry (see Section 10.3) rather than from the common PCEP TLV
registry.
Type values are chosen so that there can be commonality with Flow
Specifications defined for use with BGP [RFC8955] [RFC8956]. This is
possible because the BGP Flow Spec encoding uses a single octet to
encode the type, whereas PCEP uses 2 octets. Thus, the space of
values for the Type field is partitioned as shown in Table 1.
+=======+=======================================+
+===========+=======================================+
| Range | Description |
+=======+=======================================+
+===========+=======================================+
| 0 .. 0-255 | Per BGP Flow Spec registry defined by |
| 255 | [RFC8955] and [RFC8956]. |
| | |
| | Not to be allocated in this registry. |
+-------+---------------------------------------+
+-----------+---------------------------------------+
| 256 256-65535 | New PCEP Flow Specifications |
| .. | allocated according to the registry |
| 65535 | defined in this document. |
+-------+---------------------------------------+
+-----------+---------------------------------------+
Table 1: Flow Specification TLV Type Ranges
[RFC8955] is the reference for the "Flow Spec Component Types"
registry and defines the allocations it contains. [RFC8956]
requested for another registry the creation of the "Flow Spec IPv6 Component Types" and
requested
registry, as well as its initial allocations in it. allocations. If the AFI (in the
FLOWSPEC object) is set to IPv4, the range 0..255 is as per "Flow
Spec Component Types" [RFC8955]; if the AFI is set to IPv6, the range
0..255 is as per "Flow Spec IPv6 Component Types" [RFC8956].
The content of the Value field in each TLV is specific to the type/
AFI and describes the parameters of the Flow Specification. The
definition of the format of many of these Value fields is inherited
from BGP specifications. Specifically, the inheritance is from
[RFC8955] and [RFC8956], but it may also be inherited from future BGP
specifications.
When multiple Flow Specification TLVs are present in a single Flow
Filter TLV, they are combined to produce a more detailed
specification of a flow. For examples and rules about how this is
achieved, see [RFC8955]. As described in [RFC8955], where it says "A
given component type MAY (exactly once) be present in the Flow
Specification", a Flow Filter TLV MUST NOT contain more than one Flow
Specification TLV of the same type: an implementation that receives a
PCEP message with a Flow Filter TLV that contains more than one Flow
Specification TLV of the same type MUST respond with a PCErr message
with Error-Type 30 (FlowSpec Error) and Error-value 2 (Malformed
FlowSpec) and MUST NOT install the Flow Specification.
An implementation that receives a PCEP message carrying a Flow
Specification TLV with a type value that it does not recognize or
support MUST respond with a PCErr message with Error-Type 30
(FlowSpec Error) and Error-value 1 (Unsupported FlowSpec) and MUST
NOT install the Flow Specification.
When used in other protocols (such as BGP), these Flow Specifications
are also associated with actions to indicate how traffic matching the
Flow Specification should be treated. In PCEP, however, the only
action is to associate the traffic with a tunnel and to forward
matching traffic onto that path, so no encoding of an action is
needed.
Section 8.7 describes how overlapping Flow Specifications are
prioritized and handled.
All Flow Specification TLVs with Types in the range 0 to 255 have
values defined for use in BGP (for example, in [RFC8955] and
[RFC8956]) and are set using the BGP encoding but without the type
octet (the relevant information is in the Type field of the TLV).
The Value field is padded with trailing zeros to achieve 4-byte
alignment.
This document defines the following new types:
+======+=====================+==================+
| Type | Description | Value Defined In |
+======+=====================+==================+
| 256 | Route Distinguisher | RFC 9168 |
+------+---------------------+------------------+
| 257 | IPv4 Multicast Flow | RFC 9168 |
+------+---------------------+------------------+
| 258 | IPv6 Multicast Flow | RFC 9168 |
+------+---------------------+------------------+
Table 2: Flow Specification TLV Types Defined
in this Document
To allow identification of a VPN in PCEP via a Route Distinguisher
(RD) [RFC4364], a new TLV, ROUTE-DISTINGUISHER TLV, is defined in
this document. A Flow Specification TLV with Type 256 (ROUTE-
DISTINGUISHER TLV) carries an RD value, which is used to identify
that other flow filter information (for example, an IPv4 destination
prefix) is associated with a specific VPN identified by the RD. See
Section 8.6 for further discussion of VPN identification.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=256 | Length=8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Distinguisher |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: The Format of the ROUTE-DISTINGUISHER TLV
The format of the RD is as per [RFC4364].
Although it may be possible to describe a multicast Flow
Specification from the combination of other Flow Specification TLVs
with specific values, it is more convenient to use a dedicated Flow
Specification TLV. Flow Specification TLVs with Type values 257 and
258 are used to identify a multicast flow for IPv4 and IPv6,
respectively. The Value field is encoded as shown in Figure 4.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |S|G| Src Mask Len | Grp Mask Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Source Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Group multicast Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Multicast Flow Specification TLV Encoding
The address fields and address mask lengths of the two Multicast Flow
Specification TLVs contain source and group prefixes for matching
against packet flows noting flows. Note that the two address fields are 32 bits
for an IPv4 Multicast Flow and 128 bits for an IPv6 Multicast Flow.
The Reserved field MUST be set to zero and ignored on receipt.
Two bit flags (S and G) are defined to describe the multicast
wildcarding in use. If the S bit is set, then source wildcarding is
in use, and the values in the Source Mask Length and Source Address
fields MUST be ignored. If the G bit is set, then group wildcarding
is in use, and the values in the Group Mask Length and Group
multicast Address fields MUST be ignored. The G bit MUST NOT be set
unless the S bit is also set: if a Multicast Flow Specification TLV
is received with S bit = 0 and G bit = 1, the receiver MUST respond
with a PCErr with Error-Type 30 (FlowSpec Error) and Error-value 2
(Malformed FlowSpec).
The three multicast mappings may be achieved as follows:
(S, G) - S bit = 0, G bit = 0, the Source Address and Group
multicast Address prefixes are both used to define the multicast
flow.
(*, G) - S bit = 1, G bit = 0, the Group multicast Address prefix
is used to define the multicast flow, but the Source Address
prefix is ignored.
(*, *) = - S bit = 1, G bit = 1, the Source Address and Group
multicast Address prefixes are both ignored.
8. Detailed Procedures
This section outlines some specific detailed procedures for using the
protocol extensions defined in this document.
8.1. Default Behavior and Backward Compatibility
The default behavior is that no Flow Specification is applied to a
tunnel. That is, the default is that the FLOWSPEC object is not
used, as is the case in all systems before the implementation of this
specification.
In this case, it is a local matter (such as through configuration)
how tunnel head ends are instructed in terms of what traffic to place
on a tunnel.
[RFC5440] describes how receivers respond when they see unknown PCEP
objects.
8.2. Composite Flow Specifications
Flow Specifications may be represented by a single Flow Specification
TLV or may require a more complex description using multiple Flow
Specification TLVs. For example, a flow indicated by a source-
destination pair of IPv6 addresses would be described by the
combination of Destination IPv6 Prefix and Source IPv6 Prefix Flow
Specification TLVs.
8.3. Modifying Flow Specifications
A PCE may want to modify a Flow Specification associated with a
tunnel, or a PCC may want to report a change to the Flow
Specification it is using with a tunnel.
It is important to identify the specific Flow Specification so it is
clear that this is a modification of an existing flow and not the
addition of a new flow as described in Section 8.4. The FS-ID field
of the PCEP FLOWSPEC object is used to identify a specific Flow
Specification in the context of the content of the Speaker Entity
Identifier TLV.
When modifying a Flow Specification, all Flow Specification TLVs for
the intended specification of the flow MUST be included in the PCEP
FLOWSPEC object. The FS-ID MUST be retained from the previous
description of the flow, and the same Speaker Entity Identity Identifier TLV
MUST be used.
8.4. Multiple Flow Specifications
It is possible that traffic from multiple flows will be placed on a
single tunnel. In some cases, it is possible to define these within
a single PCEP FLOWSPEC object by widening the scope of a Flow
Specification TLV: for example, traffic to two destination IPv4
prefixes might be captured by a single Flow Specification TLV with
type "Destination" with a suitably adjusted prefix. However, this is
unlikely to be possible in most scenarios, and it must be recalled
that it is not permitted to include two Flow Specification TLVs of
the same type within one Flow Filter TLV.
The normal procedure, therefore, is to carry each Flow Specification
in its own PCEP FLOWSPEC object. Multiple objects may be present on
a single PCEP message, or multiple PCEP messages may be used.
8.5. Adding and Removing Flow Specifications
The Remove bit in the PCEP FLOWSPEC object is left clear when a Flow
Specification is being added or modified.
To remove a Flow Specification, a PCEP FLOWSPEC object is included
with the FS-ID matching the one being removed, and the R bit is set
to indicate removal. In this case, it is not necessary to include
any Flow Specification TLVs.
If the R bit is set and Flow Specification TLVs are present, an
implementation MAY ignore them. If the implementation checks the
Flow Specification TLVs against those recorded for the FS-ID and
Speaker Entity Identity Identifier of the Flow Specification being removed and
finds a mismatch, the Flow Specification matching the FS-ID MUST
still be removed, and the implementation SHOULD record a local
exception or log.
8.6. VPN Identifiers
VPN instances are identified in BGP using RDs [RFC4364]. These
values are not normally considered to have any meaning outside of the
network, and they are not encoded in data packets belonging to the
VPNs. However, RDs provide a useful way of identifying VPN instances
and are often manually or automatically assigned to VPNs as they are
provisioned.
Thus, the RD provides a useful way to indicate that traffic for a
particular VPN should be placed on a given tunnel. The tunnel head
end will need to interpret this Flow Specification not as a filter on
the fields of data packets but rather using the other mechanisms that
it already uses to identify VPN traffic. This These mechanisms could be
based on the incoming port (for port-based VPNs) or may leverage
knowledge of the VPN Routing and Forwarding (VRF) that is in use for
the traffic.
8.7. Priorities and Overlapping Flow Specifications
Flow Specifications can overlap. For example, two different Flow
Specifications may be identical except for the length of the prefix
in the destination address. In these cases, the PCC must determine
how to prioritize the Flow Specifications so as to know which path to
assign packets that match both Flow Specifications. That is, the PCC
must assign a precedence to the Flow Specifications so that it checks
each incoming packet for a match in a predictable order.
The processing of BGP Flow Specifications is described in [RFC8955].
Section 5.1 of that document explains the order of traffic filtering
rules to be executed by an implementation of that specification.
PCCs MUST apply the same ordering rules as defined in [RFC8955].
Furthermore, it is possible that Flow Specifications will be
distributed by BGP as well as by PCEP as described in this document.
In such cases, implementations supporting both approaches MUST apply
the prioritization and ordering rules as set out in [RFC8955]
regardless of which protocol distributed the Flow Specifications.
However, implementations MAY provide a configuration control to allow
one protocol to take precedence over the other; this may be
particularly useful if the Flow Specifications make identical matches
on traffic but have different actions. It is RECOMMENDED that a
message be logged for the operator to understand the behavior when
two Flow Specifications distributed by different protocols overlap,
especially when one acts to replace another.
Section 12.1 of this document covers manageability considerations
relevant to the prioritized ordering of Flow Specifications.
An implementation that receives a PCEP message carrying a Flow
Specification that it cannot resolve against other Flow
Specifications already installed (for example, because the new Flow
Specification has irresolvable conflicts with other Flow
Specifications that are already installed) MUST respond with a PCErr
message with Error-Type 30 (FlowSpec Error) and Error-value 3
(Unresolvable Conflict) and MUST NOT install the Flow Specification.
9. PCEP Messages
This section describes the format of messages that contain FLOWSPEC
objects. The only difference from previous message formats is the
inclusion of that object.
The figures in this section use the notation defined in [RFC5511].
The FLOWSPEC object is OPTIONAL and MAY be carried in the PCEP
messages.
The PCInitiate message is defined in [RFC8281] and updated as below:
<PCInitiate Message> ::= <Common Header>
<PCE-initiated-lsp-list>
Where:
<PCE-initiated-lsp-list> ::= <PCE-initiated-lsp-request>
[<PCE-initiated-lsp-list>]
<PCE-initiated-lsp-request> ::=
( <PCE-initiated-lsp-instantiation>|
<PCE-initiated-lsp-deletion> )
<PCE-initiated-lsp-instantiation> ::= <SRP>
<LSP>
[<END-POINTS>]
<ERO>
[<attribute-list>]
[<flowspec-list>]
Where:
<flowspec-list> ::= <FLOWSPEC> [<flowspec-list>]
The PCUpd message is defined in [RFC8231] and updated as below:
<PCUpd Message> ::= <Common Header>
<update-request-list>
Where:
<update-request-list> ::= <update-request>
[<update-request-list>]
<update-request> ::= <SRP>
<LSP>
<path>
[<flowspec-list>]
Where:
<path>::= <intended-path><intended-attribute-list>
<flowspec-list> ::= <FLOWSPEC> [<flowspec-list>]
The PCRpt message is defined in [RFC8231] and updated as below:
<PCRpt Message> ::= <Common Header>
<state-report-list>
Where:
<state-report-list> ::= <state-report>[<state-report-list>]
<state-report> ::= [<SRP>]
<LSP>
<path>
[<flowspec-list>]
Where:
<path>::= <intended-path>
[<actual-attribute-list><actual-path>]
<intended-attribute-list>
<flowspec-list> ::= <FLOWSPEC> [<flowspec-list>]
The PCReq message is defined in [RFC5440] and updated in [RFC8231];
it is further updated below for a Flow Specification:
<PCReq Message>::= <Common Header>
[<svec-list>]
<request-list>
Where:
<svec-list>::= <SVEC>[<svec-list>]
<request-list>::= <request>[<request-list>]
<request>::= <RP>
<END-POINTS>
[<LSP>]
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<RRO>[<BANDWIDTH>]]
[<IRO>]
[<LOAD-BALANCING>]
[<flowspec-list>]
Where:
<flowspec-list> ::= <FLOWSPEC> [<flowspec-list>]
The PCRep message is defined in [RFC5440] and updated in [RFC8231];
it is further updated below for a Flow Specification:
<PCRep Message> ::= <Common Header>
<response-list>
Where:
<response-list>::=<response>[<response-list>]
<response>::=<RP>
[<LSP>]
[<NO-PATH>]
[<attribute-list>]
[<path-list>]
[<flowspec-list>]
Where:
<flowspec-list> ::= <FLOWSPEC> [<flowspec-list>]
10. IANA Considerations
This document requests that IANA allocate code points for the
protocol elements defined in this document.
10.1. PCEP Objects
IANA maintains a subregistry called "PCEP Objects" within the "Path
Computation Element Protocol (PCEP) Numbers" registry. Each PCEP
object has an Object-Class and an Object-Type, and IANA has allocated
new code points in this subregistry as follows:
+====================+==========+=======================+===========+
| Object-Class Value | Name | Object-Type | Reference |
+====================+==========+=======================+===========+
| 43 | FLOWSPEC | 0: Reserved | RFC 9168 |
| | +-----------------------+-----------+
| | | 1: Flow | RFC 9168 |
| | | Specification | |
+--------------------+----------+-----------------------+-----------+
Table 3: PCEP Objects Subregistry Additions
10.1.1. PCEP FLOWSPEC Object Flag Field
This document requests that a new subregistry, "FLOWSPEC Object Flag
Field", be created within the "Path Computation Element Protocol
(PCEP) Numbers" registry to manage the Flag field of the FLOWSPEC
object. New values are to be assigned by Standards Action [RFC8126].
Each bit should be tracked with the following qualities:
* Bit number (counting from bit 0 as the most significant bit)
* Capability description
* Defining RFC
The initial population of this registry is as follows:
+=====+================+===========+
| Bit | Description | Reference |
+=====+================+===========+
| 0-5 | Unassigned | |
+-----+----------------+-----------+
| 6 | LPM (L bit) | RFC 9168 |
+-----+----------------+-----------+
| 7 | Remove (R bit) | RFC 9168 |
+-----+----------------+-----------+
Table 4: Initial Contents of the
FLOWSPEC Object Flag Field
Registry
10.2. PCEP TLV Type Indicators
IANA maintains a subregistry called "PCEP TLV Type Indicators" within
the "Path Computation Element Protocol (PCEP) Numbers" registry.
IANA has made the following allocations in this subregistry:
+=======+=============================+===========+
| Value | Description | Reference |
+=======+=============================+===========+
| 51 | PCE-FLOWSPEC-CAPABILITY TLV | RFC 9168 |
+-------+-----------------------------+-----------+
| 52 | FLOW FILTER TLV | RFC 9168 |
+-------+-----------------------------+-----------+
Table 5: PCEP TLV Type Indicators Subregistry
Additions
10.3. Flow Specification TLV Type Indicators
IANA has created a new subregistry called "PCEP Flow Specification
TLV Type Indicators" within the "Path Computation Element Protocol
(PCEP) Numbers" registry.
Allocations from this registry are to be made according to the
following assignment policies [RFC8126]:
+=======+===================================+
+=============+===================================+
| Range | Registration Procedures |
+=======+===================================+
+=============+===================================+
| 0 .. 0-255 | Reserved - must not be allocated. |
| 255 | |
| | Usage mirrors the BGP Flow Spec |
| | registry [RFC8955] [RFC8956]. |
+-------+-----------------------------------+
+-------------+-----------------------------------+
| 256 256-64506 | Specification Required |
+-------------+-----------------------------------+
| .. | |
| 64506 | |
+-------+-----------------------------------+
| 64507 64507-65531 | First Come First Served |
+-------------+-----------------------------------+
| .. | |
| 65531 | |
+-------+-----------------------------------+
| 65532 65532-65535 | Experimental Use |
| .. | |
| 65535 | |
+-------+-----------------------------------+
+-------------+-----------------------------------+
Table 6: Registration Procedures for the PCEP
Flow Specification TLV Type Indicators
Subregistry
IANA has populated this registry with values defined in this document
as follows, taking the new values from the range 256 to 64506:
+=======+=====================+
| Value | Meaning |
+=======+=====================+
| 256 | Route Distinguisher |
+-------+---------------------+
| 257 | IPv4 Multicast |
+-------+---------------------+
| 258 | IPv6 Multicast |
+-------+---------------------+
Table 7: Initial Contents
of the PCEP Flow
Specification TLV Type
Indicators Subregistry
10.4. PCEP Error Codes
IANA maintains a subregistry called "PCEP-ERROR Object Error Types
and Values" within the "Path Computation Element Protocol (PCEP)
Numbers" registry. Entries in this subregistry are described by
Error-Type and Error-value. IANA has added the following assignment
to this subregistry:
+============+================+=========================+===========+
| Error-Type | Meaning | Error-value | Reference |
+============+================+=========================+===========+
| 30 | FlowSpec error | 0: Unassigned | RFC 9168 |
| | +-------------------------+-----------+
| | | 1: Unsupported | RFC 9168 |
| | | FlowSpec | |
| | +-------------------------+-----------+
| | | 2: Malformed | RFC 9168 |
| | | FlowSpec | |
| | +-------------------------+-----------+
| | | 3: Unresolvable | RFC 9168 |
| | | Conflict | |
| | +-------------------------+-----------+
| | | 4: Unknown | RFC 9168 |
| | | FlowSpec | |
| | +-------------------------+-----------+
| | | 5: Unsupported | RFC 9168 |
| | | LPM Route | |
| | +-------------------------+-----------+
| | | 6-255: | RFC 9168 |
| | | Unassigned | |
+------------+----------------+-------------------------+-----------+
Table 8: PCEP-ERROR Object Error Types and Values Subregistry
Additions
10.5. PCE Capability Flag
IANA has registered a new capability bit in the OSPF Parameters "Path
Computation Element (PCE) Capability Flags" registry as follows:
+=====+========================+===========+
| Bit | Capability Description | Reference |
+=====+========================+===========+
| 16 | FlowSpec | RFC 9168 |
+-----+------------------------+-----------+
Table 9: Path Computation Element (PCE)
Capability Flags Registry Additions
11. Security Considerations
We may assume that a system that utilizes a remote PCE is subject to
a number of vulnerabilities that could allow spurious LSPs or SR
paths to be established or that could result in existing paths being
modified or torn down. Such systems, therefore, apply security
considerations as described in [RFC5440], Section 2.5 of [RFC6952],
[RFC8253], and [RFC8955].
The description of Flow Specifications associated with paths set up
or controlled by a PCE adds a further detail that could be attacked
without tearing down LSPs or SR paths but causes traffic to be
misrouted within the network. Therefore, the use of the security
mechanisms for PCEP referenced above is important.
Visibility into the information carried in PCEP does not have direct
privacy concerns for end users' data; however, knowledge of how data
is routed in a network may make that data more vulnerable. Of
course, the ability to interfere with the way data is routed also
makes the data more vulnerable. Furthermore, knowledge of the
connected endpoints (such as multicast receivers or VPN sites) is
usually considered private customer information. Therefore,
implementations or deployments concerned with protecting privacy MUST
apply the mechanisms described in the documents referenced above, in
particular, to secure the PCEP session using IPsec per Sections 10.4
to 10.6 of [RFC5440] or TLS per [RFC8253]. Note that TCP-MD5
security as originally suggested in [RFC5440] does not provide
sufficient security or privacy guarantees and SHOULD NOT be relied
upon.
Experience with Flow Specifications in BGP systems indicates that
they can become complex and that the overlap of Flow Specifications
installed in different orders can lead to unexpected results.
Although this is not directly a security issue per se, the confusion
and unexpected forwarding behavior may be engineered or exploited by
an attacker. Furthermore, this complexity might give rise to a
situation where the forwarding behaviors might create gaps in the
monitoring and inspection of particular traffic or provide a path
that avoids expected mitigations. Therefore, implementers and
operators SHOULD pay careful attention to the manageability
considerations described in Section 12 and familiarize themselves
with the careful explanations in [RFC8955].
12. Manageability Considerations
The feature introduced by this document enables operational
manageability of networks operated in conjunction with a PCE and
using PCEP. Without this feature, but in In the case of a stateful active PCE or with PCE-initiated PCE-
initiated services, in the absence of this feature, additional manual
configuration is needed to tell the head ends what traffic to place
on the network services (LSPs, SR paths, etc.).
This section follows the advice and guidance of [RFC6123].
12.1. Management of Multiple Flow Specifications
Experience with Flow Specification in BGP suggests that there can be
a lot of complexity when two or more Flow Specifications overlap.
This can arise, for example, with addresses indicated using prefixes
and could cause confusion about what traffic should be placed on
which path. Unlike the behavior in a distributed routing system, it
is not important to the routing stability and consistency of the
network that each head-end implementation applies the same rules to
disambiguate overlapping Flow Specifications, but it is important
that:
* a network operator can easily find out what traffic is being
placed on which path and why. This will facilitate analysis of
the network and diagnosis of faults.
* a PCE be able to correctly predict the effect of instructions it
gives to a PCC. This will ensure that traffic is correctly placed
on the network without causing congestion or other network
inefficiencies and that traffic is correctly delivered.
To that end, a PCC MUST enable an operator to view the Flow
Specifications that it has installed, and these MUST be presented in
order of precedence such that when two Flow Specifications overlap,
the one that will be serviced with higher precedence is presented to
the operator first.
A discussion of precedence ordering for Flow Specifications is found
in Section 8.7.
12.2. Control of Function through Configuration and Policy
Support for the function described in this document implies that a
functional element that is capable of requesting that a PCE compute
and control a path is also able to configure the specification of
what traffic should be placed on that path. Where there is a human
involved in this action, configuration of the Flow Specification must
be available through an interface (such as a graphical user interface
or a Command Line Interface). Where a distinct software component
(i.e., one not co-implemented with the PCE) is used, a protocol
mechanism will be required that could be PCEP itself or a data model,
such as extensions to the YANG model for requesting path computation
[TEAS-YANG-PATH].
Implementations MAY be constructed with a configurable switch to say
indicate whether they support the functions defined in this document.
Otherwise, such implementations MUST indicate that they support the
function as described in Section 4. If an implementation supports allows
configurable support of this function, that support MAY be
configurable per peer or once for the whole implementation.
As mentioned in Section 12.1, a PCE implementation SHOULD provide a
mechanism to configure variations in the precedence ordering of Flow
Specifications per PCC.
12.3. Information and Data Models
The YANG model in [PCE-PCEP-YANG] can be used to model and monitor
PCEP states and messages. To make that YANG model useful for the
extensions described in this document, it would need to be augmented
to cover the new protocol elements.
Similarly, as noted in Section 12.2, the YANG model defined in
[TEAS-YANG-PATH] could be extended to allow the specification of Flow
Specifications.
Finally, as mentioned in Section 12.1, a PCC implementation SHOULD
provide a mechanism to allow an operator to read the Flow
Specifications from a PCC and to understand in what order they will
be executed. This could be achieved using a new YANG model.
12.4. Liveness Detection and Monitoring
The extensions defined in this document do not require any additional
liveness detection and monitoring support. See [RFC5440] and
[RFC5886] for more information.
12.5. Verifying Correct Operation
The chief element of operation that needs to be verified (in addition
to the operation of the protocol elements as described in [RFC5440])
is the installation, precedence, and correct operation of the Flow
Specifications at a PCC.
In addition to the YANG model, for reading Flow Specifications
described in Section 12.3, tools may be needed to inject Operations
and Management (OAM) traffic at the PCC that matches specific
criteria so that it can be monitored while traveling along the
desired path. Such tools are outside the scope of this document.
12.6. Requirements for Other Protocols and Functional Components
This document places no requirements on other protocols or
components.
12.7. Impact on Network Operation
The use of the features described in this document clearly have an
important impact on network traffic since they cause traffic to be
routed on specific paths in the network. However, in practice, these
changes make no direct changes to the network operation because
traffic is already placed on those paths using some pre-existing
configuration mechanism. Thus, the significant change is the
reduction in mechanisms that have to be applied rather than a change
to how the traffic is passed through the network.
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://www.rfc-editor.org/info/rfc4760>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[RFC5511] Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
Used to Form Encoding Rules in Various Routing Protocol
Specifications", RFC 5511, DOI 10.17487/RFC5511, April
2009, <https://www.rfc-editor.org/info/rfc5511>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for Stateful PCE", RFC 8231,
DOI 10.17487/RFC8231, September 2017,
<https://www.rfc-editor.org/info/rfc8231>.
[RFC8232] Crabbe, E., Minei, I., Medved, J., Varga, R., Zhang, X.,
and D. Dhody, "Optimizations of Label Switched Path State
Synchronization Procedures for a Stateful PCE", RFC 8232,
DOI 10.17487/RFC8232, September 2017,
<https://www.rfc-editor.org/info/rfc8232>.
[RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
"PCEPS: Usage of TLS to Provide a Secure Transport for the
Path Computation Element Communication Protocol (PCEP)",
RFC 8253, DOI 10.17487/RFC8253, October 2017,
<https://www.rfc-editor.org/info/rfc8253>.
[RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for PCE-Initiated LSP Setup in a Stateful PCE
Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
<https://www.rfc-editor.org/info/rfc8281>.
[RFC8955] Loibl, C., Hares, S., Raszuk, R., McPherson, D., and M.
Bacher, "Dissemination of Flow Specification Rules",
RFC 8955, DOI 10.17487/RFC8955, December 2020,
<https://www.rfc-editor.org/info/rfc8955>.
[RFC8956] Loibl, C., Ed., Raszuk, R., Ed., and S. Hares, Ed.,
"Dissemination of Flow Specification Rules for IPv6",
RFC 8956, DOI 10.17487/RFC8956, December 2020,
<https://www.rfc-editor.org/info/rfc8956>.
13.2. Informative References
[BGP-L2VPN]
Hao, W., Eastlake, D. E., Litkowski, S., and S. Zhuang,
"BGP Dissemination of L2 Flow Specification Rules", Work
in Progress, Internet-Draft, draft-ietf-idr-flowspec-
l2vpn-18, 24 October 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-
flowspec-l2vpn-18>.
[NUMERIC-IDS-SEC]
Gont, F. and I. Arce, "Security Considerations for
Transient Numeric Identifiers Employed in Network
Protocols", Work in Progress, Internet-Draft, draft-gont-
numeric-ids-sec-considerations-06, 5 December 2020,
<https://datatracker.ietf.org/doc/html/draft-gont-numeric-
ids-sec-considerations-06>.
[PCE-PCEP-YANG]
Dhody, D., Hardwick, J., Beeram, V. P., and J. Tantsura,
"A YANG Data Model for Path Computation Element
Communications Protocol (PCEP)", Work in Progress,
Internet-Draft, draft-ietf-pce-pcep-yang-17, 23 October
2021, <https://datatracker.ietf.org/doc/html/draft-ietf-
pce-pcep-yang-17>.
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<https://www.rfc-editor.org/info/rfc4655>.
[RFC5088] Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
Zhang, "OSPF Protocol Extensions for Path Computation
Element (PCE) Discovery", RFC 5088, DOI 10.17487/RFC5088,
January 2008, <https://www.rfc-editor.org/info/rfc5088>.
[RFC5089] Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
Zhang, "IS-IS Protocol Extensions for Path Computation
Element (PCE) Discovery", RFC 5089, DOI 10.17487/RFC5089,
January 2008, <https://www.rfc-editor.org/info/rfc5089>.
[RFC5886] Vasseur, JP., Ed., Le Roux, JL., and Y. Ikejiri, "A Set of
Monitoring Tools for Path Computation Element (PCE)-Based
Architecture", RFC 5886, DOI 10.17487/RFC5886, June 2010,
<https://www.rfc-editor.org/info/rfc5886>.
[RFC6123] Farrel, A., "Inclusion of Manageability Sections in Path
Computation Element (PCE) Working Group Drafts", RFC 6123,
DOI 10.17487/RFC6123, February 2011,
<https://www.rfc-editor.org/info/rfc6123>.
[RFC6952] Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
BGP, LDP, PCEP, and MSDP Issues According to the Keying
and Authentication for Routing Protocols (KARP) Design
Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013,
<https://www.rfc-editor.org/info/rfc6952>.
[RFC7399] Farrel, A. and D. King, "Unanswered Questions in the Path
Computation Element Architecture", RFC 7399,
DOI 10.17487/RFC7399, October 2014,
<https://www.rfc-editor.org/info/rfc7399>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8283] Farrel, A., Ed., Zhao, Q., Ed., Li, Z., and C. Zhou, "An
Architecture for Use of PCE and the PCE Communication
Protocol (PCEP) in a Network with Central Control",
RFC 8283, DOI 10.17487/RFC8283, December 2017,
<https://www.rfc-editor.org/info/rfc8283>.
[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
DOI 10.17487/RFC8664, December 2019,
<https://www.rfc-editor.org/info/rfc8664>.
[TEAS-YANG-PATH]
Busi, I., Belotti, S., Lopez, V., Sharma, A., and Y. Shi,
"YANG Data Model for requesting Path Computation", Work in
Progress, Internet-Draft, draft-ietf-teas-yang-path-
computation-16, 6 September 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-
yang-path-computation-16>.
Acknowledgements
Thanks to Julian Lucek, Sudhir Cheruathur, Olivier Dugeon, Jayant
Agarwal, Jeffrey Zhang, Acee Lindem, Vishnu Pavan Beeram, Julien
Meuric, Deborah Brungard, Éric Vyncke, Erik Kline, Benjamin Kaduk,
Martin Duke, Roman Danyliw, and Alvaro Retana for useful discussions
and comments.
Contributors
Shankara
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore 560066
Karnataka
India
Email: shankara@huawei.com
Qiandeng Liang
Huawei Technologies
Yuhuatai District
101 Software Avenue,
Nanjing, 210012
China
Email: liangqiandeng@huawei.com
Cyril Margaria
Juniper Networks
200 Somerset Corporate Boulevard, Suite 4001
Bridgewater, NJ 08807
United States of America
Email: cmargaria@juniper.net
Colby Barth
Juniper Networks
200 Somerset Corporate Boulevard, Suite 4001
Bridgewater, NJ 08807
United States of America
Email: cbarth@juniper.net
Xia Chen
Huawei Technologies
Huawei Bld., No. 156 Beiqing Rd.
Beijing, 100095
China
Email: jescia.chenxia@huawei.com
Shunwan Zhuang
Huawei Technologies
Huawei Bld., No. 156 Beiqing Rd.
Beijing, 100095
China
Email: zhuangshunwan@huawei.com
Cheng Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing, 100095
China
Email: c.l@huawei.com
Authors' Addresses
Dhruv Dhody
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore 560066
Karnataka
India
Email: dhruv.ietf@gmail.com
Adrian Farrel
Old Dog Consulting
Email: adrian@olddog.co.uk
Zhenbin Li
Huawei Technologies
Huawei Bldg., No. 156 Beiqing Rd.
Beijing
100095
China
Email: lizhenbin@huawei.com