wdiff rfc8379.alt-original rfc8379.txt

Open Shortest Path First IGP
Internet Engineering Task Force (IETF) S. Hegde
Internet-Draft
Request for Comments: 8379 Juniper Networks, Inc.
Intended status:
Category: Standards Track P. Sarkar
Expires: August 8, 2018
ISSN: 2070-1721 Arrcus, Inc.
H. Gredler
Individual
RtBrick Inc.
M. Nanduri
ebay Corporation
L. Jalil
Verizon
February 4,
April 2018

OSPF Graceful Link shutdown
draft-ietf-ospf-link-overload-16 Shutdown

Abstract

When a link is being prepared to be taken out of service, the traffic
needs to be diverted from both ends of the link. Increasing the
metric to the highest value on one side of the link is not sufficient
to divert the traffic flowing in the other direction.

It is useful for the routers in an OSPFv2 or OSPFv3 routing domain to
be able to advertise a link as being in a graceful-shutdown state to
indicate impending maintenance activity on the link. This
information can be used by the network devices to re-route reroute the traffic
effectively.

This document describes the protocol extensions to disseminate
graceful-link-shutdown information in OSPFv2 and OSPFv3.

Status of This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum 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 six months this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

This Internet-Draft will expire on August 8, 2018.
https://www.rfc-editor.org/info/rfc8379.

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Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Flooding Scope . . . . . . . . . . . . . . . . . . . . . . . 4
4. Protocol Extensions . . . . . . . . . . . . . . . . . . . . . 4
4.1. OSPFv2 graceful-link-shutdown sub-TLV Graceful-Link-Shutdown Sub-TLV . . . . . . . . . . 4
4.2. Remote IPv4 Address Sub-TLV . . . . . . . . . . . . . . . 4
4.3. Local/Remote Interface ID Sub-TLV . . . . . . . . . . . . 5
4.4. OSPFv3 Graceful-Link-Shutdown sub-TLV Sub-TLV . . . . . . . . . . 6
4.5. BGP-LS Graceful-Link-Shutdown TLV . . . . . . . . . . . . 6
4.6. Distinguishing parallel links Parallel Links . . . . . . . . . . . . . . 7
5. Elements of procedure Procedure . . . . . . . . . . . . . . . . . . . . 8
5.1. Point-to-point links Point-to-Point Links . . . . . . . . . . . . . . . . . . 9
5.2. Broadcast/NBMA links Links . . . . . . . . . . . . . . . . . . 9
5.3. Point-to-multipoint links Point-to-Multipoint Links . . . . . . . . . . . . . . . . 10
5.4. Unnumbered interfaces Interfaces . . . . . . . . . . . . . . . . . . 10
5.5. Hybrid Broadcast and P2MP interfaces Interfaces . . . . . . . . . . 10
6. Backward compatibility Compatibility . . . . . . . . . . . . . . . . . . . 10 11
7. Applications . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Overlay Network . . . . . . . . . . . . . . . . . . . . . 11
7.2. Controller based Controller-Based Deployments . . . . . . . . . . . . . . 12
7.3. L3VPN Services and sham-links Sham Links . . . . . . . . . . . . . . 13
7.4. Hub and spoke deployment Spoke Deployment . . . . . . . . . . . . . . . . 13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 13
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 14
10. Acknowledgements References . . . . . . . . . . . . . . . . . . . . . . . . . 14
11.
10.1. Normative References . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . 14
11.1. Normative References . . . . . . . . . . 15
Acknowledgements . . . . . . . . 14
11.2. Informative References . . . . . . . . . . . . . . . . . 15 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16

1. Introduction

This document describes a mechanism for gracefully taking a link out
of service while allowing it to be used if no other path is
available.It
available. It also provides a mechanism to divert the traffic from
both directions of the link.

Many OSPFv2 or OSPFv3 deployments run on overlay networks provisioned
by means of pseudo-wires pseudowires or L2-circuits. L2 circuits. Prior to devices in the
underlying network going offline for maintenance, it is useful to
divert the traffic away from the node before the maintenance is actually
performed. Since the nodes in the underlying network are not visible
to OSPF, the existing stub router stub-router mechanism described in [RFC6987]
cannot be used. In a service provider's network, there may be many
CE-to-CE connections that run over a single PE. It is cumbersome to
change the metric on every CE-to-CE connection in both directions.
This document provides a mechanism to change the metric of the link
on the remote side and also use the link as a last-resort- last-resort link if no
alternate paths are available. An application specific to this use
case is described in detail in Section 7.1.

This document provides mechanisms to advertise graceful-link-shutdown
state in the flexible encodings provided by OSPFv2 "OSPFv2 Prefix/Link
Attribute Advertisement Advertisement" [RFC7684] and the E-Router-LSA
[I-D.ietf-ospf-ospfv3-lsa-extend] fr [RFC8362] for
OSPFv3. Throughout this document, OSPF is used when the text applies
to both OSPFv2 and OSPFv3. OSPFv2 or OSPFv3 is used when the text is
specific to one version of the OSPF protocol.

1.1. Requirements Language

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 RFC 2119 [RFC2119]. BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

2. Motivation

The motivation of this document is to reduce manual intervention
during maintenance activities. The following objectives help to
accomplish this in a range of deployment scenarios.

1. Advertise impending maintenance activity so that traffic from
both directions can be diverted away from the link.

2. Allow the solution to be backward compatible so that nodes that
do not understand the new advertisement, advertisement do not cause routing
loops.

3. Advertise the maintenance activity to other nodes in the network
so that LSP Label Switched Path (LSP) ingress routers/controllers can
learn about the impending maintenance activity and apply specific
policies to re-
route reroute the LSPs for traffic-engineering deployments based deployments. on Traffic
Engineering (TE).

4. Allow the link to be used as a last resort last-resort link to prevent
traffic disruption when alternate paths are not available.

3. Flooding Scope

The graceful-link-shutdown information is flooded in an area-scoped
Extended Link Opaque LSA [RFC7684] for OSPFv2 and in an E-Router-LSA
for OSPFv3 [I-D.ietf-ospf-ospfv3-lsa-extend]. [RFC8362]. The Graceful-Link-Shutdown sub-TLV MAY be
processed by the head-end nodes or the controller as described in the
Section 7. The procedures for processing the Graceful-Link-Shutdown
sub-TLV are described in Section 5.

4. Protocol Extensions

4.1. OSPFv2 graceful-link-shutdown sub-TLV Graceful-Link-Shutdown Sub-TLV

The Graceful-Link-Shutdown sub-TLV identifies the link as being
gracefully shutdown. It is advertised in extended the Extended Link TLV of
the Extended Link Opaque LSA as defined in [RFC7684].

Figure 1: Graceful-Link-Shutdown sub-TLV Sub-TLV for OSPFv2

Type : TBA (suggested value 7)

Type: 7

Length: 0

4.2. Remote IPv4 Address Sub-TLV

This sub-TLV specifies the IPv4 address of the remote endpoint on the
link. It is advertised in the Extended Link TLV as defined in
[RFC7684]. This sub-TLV is optional and MAY be advertised in an
area-scoped Extended Link Opaque LSA to identify the link when there
are multiple parallel links between two nodes.

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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote IPv4 address Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: Remote IPv4 Address Sub-TLV

Type : TBA (suggested value 8)

Type: 8

Length: 4

Value: Remote IPv4 address. The remote IPv4 address is used to
identify a particular link on the remote side when there are multiple
parallel links between two nodes.

4.3. Local/Remote Interface ID Sub-TLV

This sub-TLV specifies local Local and remote interface identifiers. Remote Interface IDs. It is
advertised in the Extended Link TLV as defined in [RFC7684]. This
sub-TLV is optional and MAY be advertised in an area-scoped Extended
Link Opaque LSA to identify the link when there are multiple parallel
unnumbered links between two nodes. The local interface-id Local Interface ID is
generally readily available. One of the mechanisms to obtain remote
interface-id the
Remote Interface ID is described in [RFC4203].

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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 3: Local/Remote Interface ID Sub-TLV

Type : TBA (suggested value 9)

Type: 9

Length: 8

Value: 4 octets of the Local Interface ID followed by 4 octets of the
Remote
interface Interface ID.

4.4. OSPFv3 Graceful-Link-Shutdown sub-TLV Sub-TLV

The Graceful-Link-Shutdown sub-TLV is carried in the Router-Link TLV
as defined in the [I-D.ietf-ospf-ospfv3-lsa-extend] [RFC8362] for OSPFv3. The Router-Link TLV contains the neighbour interface-id
Neighbor Interface ID and can uniquely identify the link on the
remote node.

Figure 4: Graceful-Link-Shutdown sub-TLV Sub-TLV for OSPFv3

Type : TBA (Suggested value 7)

Type: 8

Length: 0

4.5. BGP-LS Graceful-Link-Shutdown TLV

BGP-LS as defined in [RFC7752] is a mechanism to distribute that distributes
network information to the external entities using the BGP routing
protocol.
Graceful-link-shutdown Graceful link shutdown is an important link information that
the external entities can use for various use cases as defined in
Section 7. BGP Link NLRI Network Layer Reachability Information (NLRI) is
used to carry the link information. A new TLV called Graceful-Link-Shutdown "Graceful-Link-
Shutdown" is defined to describe the link attribute corresponding to
graceful-link-shutdown state. The TLV format is as described in [RFC7752] sec 3.1.
Section 3.1 of [RFC7752]. There is no value field Value field, and length the Length
field is set to zero for this TLV.

Figure 5: Graceful-Link-Shutdown TLV for BGP-LS

Type : TBA (Suggested value 1121)

Type: 1121

Length: 0

4.6. Distinguishing parallel links Parallel Links

++++++++++I.w I.y +++++++++ I.y+++++++++++
|Router A|------------------|Router B |
| |------------------| |
++++++++++I.x I.z++++++++++ I.z+++++++++++

Figure 6: Parallel Linkls Links

Consider two routers routers, A and B B, connected with two parallel point-to-
point
point-to-point interfaces. I.w and I.x represent the Interface interface
address on Router A's side side, and I.y and I.z represent Interface interface
addresses on Router B's side. The extended link opaque Extended Link Opaque LSA as described
defined in [RFC7684] describes links using link-type, Link-ID Link Type, Link ID, and Link-data.
For ex.
Link Data. For example, a link with the address I.w is described as
below on Router A.

Link-type

Link Type = Point-to-point

Link-ID: Router-ID

Link ID = Router ID of B

Link-Data

Link Data = I.w
A third node (controller or head-end) in the network cannot
distinguish the Interface interface on router B Router B, which is connected to this
particular Interface with on Router A based on the above information. Interface link information
described above. The interface with address I.y or I.z could be
chosen due to this ambiguity. In such
cases Remote-IPv4 cases, a Remote IPv4 Address
sub-TLV should be originated and added to the Extended Link TLV. The
use cases as described in Section 7 require controller or head-end
nodes to interpret the graceful-link-
shutdown graceful-link-shutdown information and hence
the need for the Remote IPv4 address Address sub-TLV. I.y is carried in the
Extended Link TLV TLV, which unambiguously identifies the interface on
the remote side. The OSPFv3 Router-link-TLV Router-Link TLV as described in [I-D.ietf-ospf-ospfv3-lsa-extend]
[RFC8362] contains an Interface ID and a neighbor's Interface-ID Interface ID,
which can uniquely identify connecting the interface on the remote side and hence
side; hence, OSPFv3 does not require
seperate Remote-IPv6 a separate remote IPv6 address
to be advertised along with the OSPFv3- OSPFv3 Graceful-Link-Shutdown sub-TLV. sub-
TLV.

5. Elements of procedure Procedure

As defined in [RFC7684] [RFC7684], every link on the node will have a separate
Extended Link Opaque LSA. The node that has the link to be taken out
of service MUST advertise the Graceful-Link-Shutdown sub-TLV in the
Extended Link TLV of the Extended Link Opaque LSA for OSPFv2, as
defined in
[RFC7684] for OSPFv2 [RFC7684], and in the Router-Link TLV of E-Router-LSA for
OSPFv3. The Graceful-Link-Shutdown sub-TLV indicates that the link
identified by the sub-TLV is subjected to maintenance.

For the purposes of changing the metric OSPFv2 and OSPFv3 Router-LSAs
need to be re-orignated and for reoriginated. To change the Traffic Engineering metric,
TE Opaque LSAs [RFC3630] in OSPFv2 [RFC3630] and Intra-area-TE-LSA [RFC5329]in Intra-area-TE-LSAs in OSPFv3
[RFC5329] need to be re-originated. reoriginated.

The Graceful-Link-Shutdown graceful-link-shutdown information is advertised as a property of
the link and is flooded through the area. This information can be
used by ingress routers or controllers to take special actions. An
application specific to this use case is described in Section 7.2.

When a link is ready to carry traffic, the Graceful-Lnk-Shutdown sub-
TLV Graceful-Link-Shutdown
sub-TLV MUST be removed from the Extended Link TLV/Router-Link TLV TLV,
and the corresponding LSAs MUST be readvertised. Similarly, the
metric MUST be set to original values values, and the corresponding LSAs
MUST be readvertised.

The procedures described in this draft document may be used to divert the
traffic away from the link in scenarios other than link-shutdown or
link-replacement activity.

The precise action taken by the remote node at the other end of the
link identified for graceful-shutdown depends on the link type.

5.1. Point-to-point links Point-to-Point Links

The node that has the link to be taken out of service MUST set the
metric of the link to MaxLinkMetric (0xffff) and re-originate reoriginate its router-
LSA.
Router-LSA. The Traffic Engineering metric of the link SHOULD be set
to
(0xffffffff) (0xffffffff), and the node SHOULD re-originate reoriginate the corresponding TE
Link Opaque LSAs. When a Graceful-Link-Shutdown sub-TLV is received
for a point-to-point link, the remote node MUST identify the local
link which that corresponds to the graceful-shutdown link and set its
metric to MaxLinkMetric (0xffff) (0xffff), and the remote node MUST re-
originate
reoriginate its router-LSA Router-LSA with the changed metric. When TE is
enabled, the Traffic Engineering metric of the link SHOULD be set to
(0xffffffff) and follow the procedures of in [RFC5817]. Similarly, the
remote node SHOULD set the Traffic Engineering metric of the link to
0xffffffff and SHOULD re-originate reoriginate the TE Link Opaque LSA for the link
with the new value.

The Extended link opaque Link Opaque LSAs and the Extended link Link TLV are not
scoped for multi-topology [RFC4915]. In multi-topology deployments
[RFC4915], the Graceful-Link-Shutdown sub-TLV advertised in an
Extended Link opaque Opaque LSA corresponds to all the topologies which that
include the link. The receiver node SHOULD change the metric in the
reverse direction for all the topologies which that include the remote link
and re-originate reoriginate the router-LSA Router-LSA as defined in [RFC4915].

When the originator of the Graceful-Link-Shutdown sub-TLV purges the
Extended Link Opaque LSA or re-originates reoriginates it without the Graceful-
Link-Shutdown
Graceful-Link-Shutdown sub-TLV, the remote node must re-originate reoriginate the
appropriate LSAs with the metric and TE metric values set to their
original values.

5.2. Broadcast/NBMA links Links

Broadcast or NBMA Non-Broadcast Multi-Access (NBMA) networks in OSPF are
represented by a star topology where the Designated Router (DR) is
the central point to which all other routers on the broadcast or NBMA
network logically connect. As a result, routers on the broadcast or
NBMA network advertise only their adjacency to the DR. Routers that
do not act as DR DRs do not form or advertise adjacencies with each
other. For the Broadcast broadcast links, the MaxLinkMetric on the remote link
cannot be changed since all the neighbors are on same link. Setting
the link cost to MaxLinkMetric would impact paths going via all neighbors. paths that traverse
any of the neighbors connected on that broadcast link.

The node that has the link to be taken out of service MUST set the
metric of the link to MaxLinkMetric (0xffff) and re-originate reoriginate the Router-
LSA.
Router-LSA. The Traffic Engineering metric of the link SHOULD be set
to (
0xffffffff) (0xffffffff), and the node SHOULD re-originate reoriginate the corresponding TE
Link Opaque LSAs. For a broadcast link, the two part two-part metric as
described in [RFC8042] is used. The node originating the Graceful-
Link-Shutdown
Graceful-Link-Shutdown sub-TLV MUST set the metric in the
Network-to-Router Metric sub-TLV to MaxLinkMetric (0xffff) for OSPFv2
and OSPFv3 and
re-originate reoriginate the corresponding LSAs. The nodes that
receive the two-
part two-part metric should follow the procedures described in
[RFC8042]. The
backward compatibility backward-compatibility procedures described in
[RFC8042] should be followed to ensure loop free loop-free routing.

5.3. Point-to-multipoint links Point-to-Multipoint Links

Operation for the point-to-multipoint (P2MP) links is similar to the point-
to-point
point-to-point links. When a Graceful-Link-Shutdown sub-TLV is
received for a point-to-multipoint link link, the remote node MUST
identify the
neighbour which neighbor that corresponds to the graceful-shutdown link
and set its metric to MaxLinkMetric (0xffff). The remote node MUST re-originate
reoriginate the router-LSA Router-LSA with the changed metric for the correponding
corresponding neighbor.

5.4. Unnumbered interfaces Interfaces

Unnumbered interfaces do not have a unique IP address and borrow
their address from other interfaces. [RFC2328] describes procedures
to handle unnumbered interfaces in the context of the router-LSA. Router-LSA. We
apply a similar procedure to the Extended Link TLV advertising the
Graceful-Link-Shutdown sub-TLV in order to handle unnumbered
interfaces. The link-data Link-Data field in the Extended Link TLV includes
the Local interface-id Interface ID instead of the IP address. The Local/Remote
Interface ID sub-TLV MUST be advertised when there are multiple
parallel unnumbered interfaces between two nodes. One of the
mechanisms to obtain the interface-id Interface ID of the remote side is defined
in [RFC4203].

5.5. Hybrid Broadcast and P2MP interfaces Interfaces

Hybrid Broadcast and P2MP interfaces represent a broadcast network
modeled as P2MP interfaces. [RFC6845] describes procedures to handle
these interfaces. Operation for the Hybrid interfaces is similar to
operation for the P2MP interfaces. When a Graceful-Link-Shutdown
sub-TLV is received for a hybrid link, the remote node MUST identify
the neighbor which that corresponds to the graceful-shutdown link and set
its metric to MaxLinkMetric (0xffff). All the remote nodes connected
to the originator MUST re-originate reoriginate the router-LSA Router-LSA with the changed
metric for the neighbor.

6. Backward compatibility Compatibility

The mechanisms described in the document are fully backward
compatible. It is required that the node adverting the Graceful-
Link-Shutdown
Graceful-Link-Shutdown sub-TLV as well as the node at the remote end
of the graceful-shutdown link support the extensions described herein
for the traffic to be diverted from the graceful-shutdown link. If
the remote node doesn't support the capability, it will still use the
graceful-shutdown link link, but there are no other adverse effects. In
the case of broadcast links using two-part metrics, the backward backward-
compatibility procedures as described in [RFC8042] are applicable.

7. Applications

7.1. Overlay Network

Many service providers offer L2 services to a customer connecting
different locations. The customer's IGP protocol creates a seamless
private network (overlay network) across the locations for the
customer. Service providers want to offer graceful-shutdown
functionality when the PE device is taken-out taken out for maintenance. There
can be large number of customers attached to a PE node node, and the
remote
end-points endpoints for these L2 attachments attachment circuits are spread across
the service provider's network. It is a tedious and error-prone process
to change Changing the metric for all
corresponding L2 circuits in both
directions. directions is a tedious and error-
prone process. The graceful-link-shutdown feature simplifies the
process by increasing the metric on the CE-CE overlay link so that
traffic in both directions is diverted away from the PE undergoing
maintenance. The Graceful-Link-Shutdown graceful-link-shutdown feature allows the link to
be used as a last resort last-resort link so that traffic is not disrupted when
alternate paths are not available.

------PE3---------------PE4------CE3
/ \
/ \
CE1---------PE1----------PE2---------CE2
\
\
------CE4

CE: Customer Edge
PE: Provider Edge

Figure 7: Overlay Network

In the example shown in Figure 7, when the PE1 node is going out of
service for maintenance, a service provider sets the PE1 to stub-
router state and communicates the pending maintenance action to the
overlay customer networks. The mechanisms used to communicate
between PE1 and CE1 is outside the scope of this document. CE1 sets
the graceful-link-shutdown state on its links connecting CE3, CE2 and
CE4 CE2,
and CE4, changes the metric to MaxLinkMetric MaxLinkMetric, and re-originates reoriginates the
corresponding LSA. The remote end of the link at CE3, CE2, and CE4
also set the metric on the link to MaxLinkMetric MaxLinkMetric, and the traffic
from both directions gets diverted away from PE1.

7.2. Controller based Controller-Based Deployments

In controller-based deployments where the controller participates in
the IGP protocol, the controller can also receive the graceful-link-
shutdown
graceful-link-shutdown information as a warning that link maintenance
is imminent. Using this information, the controller can find
alternate paths for traffic which that uses the affected link. The
controller can apply various policies and re-route reroute the LSPs away from
the link undergoing maintenance. If there are no alternate paths
satisfying the constraints, the controller might temporarily relax
those constraints and put the service on a different path.
Increasing the link metric alone does not specify the maintenance
activity as the metric could increase in events such as LDP-IGP synchronisation.
synchronization. An explicit indication from the router using the graceful-link-shutdown
Graceful-Link-Shutdown sub-TLV is needed to inform the Controller controller or
head-end routers.

_____________
| |
-------------|
--------------| Controller |--------------
| |____________ | |
| |
|--------- Primary Path ------------------|
PE1---------P1----------------P2---------PE2
| |
| |
|________P3________|

Alternate Path

Figure 8: Controller based Controller-Based Traffic Engineering

In the above example, the PE1->PE2 LSP is set-up set up to satisfy a
constraint of 10 Gbps bandwidth on each link. The links P1->P3 and
P3->P2 have only 1 Gbps capacity capacity, and there is no alternate path
satisfying the bandwidth constraint of 10Gbps. 10 Gbps. When the P1->P2 link
is being prepared for maintenance, the controller receives the
graceful-link-shutdown information, as there is no alternate path
available which that satisfies the constraints, and the controller chooses
a path that is less optimal and temporarily sets up an alternate path
via P1->P3->P2. Once the traffic is diverted, the P1->P2 link can be
taken out of service for maintenance/upgrade.

7.3. L3VPN Services and sham-links Sham Links

Many service providers offer L3VPN Layer 3 Virtual Private Network (L3VPN)
services to customers customers, and CE-PE links run OSPF [RFC4577]. When the
PE is taken out of service for maintenance, all the links on the PE
can be set to graceful-link-
shutdown state graceful-link-shutdown state, which will gurantee guarantee that
the traffic to/from dual-
homed dual-homed CEs gets diverted. The interaction
between OSPF and BGP is outside the scope of this document. [RFC6987] based A
mechanism based on [RFC6987] with summaries and externals that are
advertised with high metrics could also be used to achieve the same
functionality when implementations support high metrics advertisement
for summaries and externals.

Another useful usecase use case is when ISPs provide sham-link services to
customers [RFC4577]. When the PE goes out of service for
maintenance, all sham-links sham links on the PE can be set to graceful-link-shutdown state graceful-link-
shutdown state, and traffic can be divered diverted from both ends without
having to touch the configurations on the remote end of the sham-links. sham
links.

7.4. Hub and spoke deployment Spoke Deployment

OSPF is largely deployed in Hub and Spoke deployments with a large
number of spokes Spokes connecting to the Hub. It is a general practice to
deploy multiple Hubs with all spokes Spokes connecting to these Hubs to
achieve redundancy. The [RFC6987] mechanism defined in [RFC6987] can be used
to divert the spoke-to-spoke Spoke-to-Spoke traffic from the overloaded hub Hub router.
The traffic that flows from spokes Spokes via the hub Hub into an external
network may not be diverted in certain scenarios.When scenarios. When a Hub node
goes down for maintenance, all links on the Hub can be set to graceful-link-
shutdown state
graceful-link-shutdown state, and traffic gets divered diverted from the spoke
Spoke sites as well without having to make configuration changes on
the spokes. Spokes.

8. Security Considerations

This document utilizes the OSPF packets and LSAs described in
[RFC2328] , [RFC5340] , [RFC3630] [RFC3630], [RFC5329], and [RFC5329]. [RFC5340]. The authentication
procedures described in [RFC2328] for OSPFv2 and [RFC4552] for OSPFv3
are applicable to this document as well. This document does not
introduce any further security issues other than those discussed in
[RFC2328] and [RFC5340].

9. IANA Considerations

This specification updates one OSPF registry:

OSPFv2

IANA has registered the following in the "OSPFv2 Extended Link TLV Sub-TLVs

i)
Sub-TLVs" registry:

7 - Graceful-Link-Shutdown Sub-TLV

8 - Suggested value 7
ii) Remote IPv4 Address Sub-TLV

9 - Suggested value 8

iii) Local/Remote Interface ID Sub-TLV - Suggested Value 9

OSPFv3

IANA has registered the following value in the "OSPFv3 Extended-LSA sub-TLV Registry

i)
Sub-TLVs" registry:

8 - Graceful-Link-Shutdown sub-TLV - suggested

IANA has registered the following value 7

BGP-LS in the "BGP-LS Node
Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs [RFC7752]

i)Graceful-Link-Shutdown TLV - Suggested TLVs"
registry [RFC7752]":

1121

11. - Graceful-Link-Shutdown TLV

10. References

11.1.

10.1. Normative References

[I-D.ietf-ospf-ospfv3-lsa-extend]
Lindem, A., Roy, A., Goethals, D., Vallem, V., and F.
Baker, "OSPFv3 LSA Extendibility", draft-ietf-ospf-ospfv3-
lsa-extend-23 (work in progress), January 2018.

[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>.

[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.

[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
DOI 10.17487/RFC3630, September 2003,
<https://www.rfc-editor.org/info/rfc3630>.

[RFC5329] Ishiguro, K., Manral, V., Davey, A., and A. Lindem, Ed.,
"Traffic Engineering Extensions to OSPF Version 3",
RFC 5329, DOI 10.17487/RFC5329, September 2008,
<https://www.rfc-editor.org/info/rfc5329>.

[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.

[RFC5817] Ali, Z., Vasseur, JP., Zamfir, A., and J. Newton,
"Graceful Shutdown in MPLS and Generalized MPLS Traffic
Engineering Networks", RFC 5817, DOI 10.17487/RFC5817,
April 2010, <https://www.rfc-editor.org/info/rfc5817>.

[RFC6845] Sheth, N., Wang, L., and J. Zhang, "OSPF Hybrid Broadcast
and Point-to-Multipoint Interface Type", RFC 6845,
DOI 10.17487/RFC6845, January 2013,
<https://www.rfc-editor.org/info/rfc6845>.

[RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 6987,
DOI 10.17487/RFC6987, September 2013,
<https://www.rfc-editor.org/info/rfc6987>.

[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <https://www.rfc-editor.org/info/rfc7684>.

[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.

[RFC8042] Zhang, Z., Wang, L., and A. Lindem, "OSPF Two-Part
Metric", RFC 8042, DOI 10.17487/RFC8042, December 2016,
<https://www.rfc-editor.org/info/rfc8042>.

11.2.

[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>.

[RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
F. Baker, "OSPFv3 Link State Advertisement (LSA)
Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
2018, <https://www.rfc-editor.org/info/rfc8362>.

10.2. Informative References

[RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,
<https://www.rfc-editor.org/info/rfc4203>.

[RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality
for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
<https://www.rfc-editor.org/info/rfc4552>.

[RFC4577] Rosen, E., Psenak, P., and P. Pillay-Esnault, "OSPF as the
Provider/Customer Edge Protocol for BGP/MPLS IP Virtual
Private Networks (VPNs)", RFC 4577, DOI 10.17487/RFC4577,
June 2006, <https://www.rfc-editor.org/info/rfc4577>.

[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
RFC 4915, DOI 10.17487/RFC4915, June 2007,
<https://www.rfc-editor.org/info/rfc4915>.

10.

Acknowledgements

Thanks to Chris Bowers for valuable inputs input and edits to the document.
Thanks to Jeffrey Zhang, Acee Lindem Lindem, and Ketan Talaulikar for inputs. their
input. Thanks to Karsten Thomann for careful review and inputs input on the
applications where graceful-link-shutdown graceful link shutdown is useful.

Thanks to Alia Atlas, Deborah Brungard, Alvaro Retana, Andrew G.
Malis
Malis, and Tim Chown for their valuable inputs. input.

Authors' Addresses

Shraddha Hegde
Juniper Networks, Inc.
Embassy Business Park
Bangalore, KA 560093
India

Email: shraddha@juniper.net

Pushpasis Sarkar
Arrcus, Inc.

Email: pushpasis.ietf@gmail.com

Hannes Gredler
Individual
RtBrick Inc.

Email: hannes@gredler.at hannes@rtbrick.com
Mohan Nanduri
ebay Corporation
2025 Hamilton Avenue
San Jose, CA 98052
US
United States of America

Email: mnanduri@ebay.com

Luay Jalil
Verizon

Email: luay.jalil@verizon.com