draft-ietf-ospf-link-overload-11.txt   draft-ietf-ospf-link-overload-12.txt 
Open Shortest Path First IGP S. Hegde Open Shortest Path First IGP S. Hegde
Internet-Draft Juniper Networks, Inc. Internet-Draft Juniper Networks, Inc.
Intended status: Standards Track P. Sarkar Intended status: Standards Track P. Sarkar
Expires: July 5, 2018 H. Gredler Expires: July 20, 2018 H. Gredler
Individual Individual
M. Nanduri M. Nanduri
ebay Corporation ebay Corporation
L. Jalil L. Jalil
Verizon Verizon
January 1, 2018 January 16, 2018
OSPF Link Overload OSPF Graceful Link shutdown
draft-ietf-ospf-link-overload-11 draft-ietf-ospf-link-overload-12
Abstract Abstract
When a link is being prepared to be taken out of service, the traffic 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 needs to be diverted from both ends of the link. Increasing the
metric to the highest metric on one side of the link is not metric to the highest value on one side of the link is not sufficient
sufficient to divert the traffic flowing in the other direction. to divert the traffic flowing in the other direction.
It is useful for routers in an OSPFv2 or OSPFv3 routing domain to be It is useful for routers in an OSPFv2 or OSPFv3 routing domain to be
able to advertise a link as being in an overload state to indicate able to advertise a link as being in a graceful-shutdown state to
impending maintenance activity on the link. This information can be indicate impending maintenance activity on the link. This
used by the network devices to re-route the traffic effectively. information can be used by the network devices to re-route the
traffic effectively.
This document describes the protocol extensions to disseminate link- This document describes the protocol extensions to disseminate
overload information in OSPFv2 and OSPFv3. graceful-link-shutdown information in OSPFv2 and OSPFv3.
Requirements Language Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 5, 2018. This Internet-Draft will expire on July 20, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Flooding Scope . . . . . . . . . . . . . . . . . . . . . . . 4 3. Flooding Scope . . . . . . . . . . . . . . . . . . . . . . . 4
4. Link-Overload sub-TLV . . . . . . . . . . . . . . . . . . . . 4 4. Graceful-Link-Shutdown sub-TLV . . . . . . . . . . . . . . . 4
4.1. OSPFv2 Link-overload sub-TLV . . . . . . . . . . . . . . 4 4.1. OSPFv2 graceful-link-shutdown sub-TLV . . . . . . . . . . 4
4.2. Remote IPv4 Address Sub-TLV . . . . . . . . . . . . . . . 4 4.2. Remote IPv4 Address Sub-TLV . . . . . . . . . . . . . . . 5
4.3. Local/Remote Interface ID Sub-TLV . . . . . . . . . . . . 5 4.3. Local/Remote Interface ID Sub-TLV . . . . . . . . . . . . 5
4.4. OSPFv3 Link-Overload sub-TLV . . . . . . . . . . . . . . 6 4.4. OSPFv3 Graceful-Link-Shutdown sub-TLV . . . . . . . . . . 6
4.5. BGP-LS Link-overload TLV . . . . . . . . . . . . . . . . 6 4.5. BGP-LS Graceful-Link-Shutdown TLV . . . . . . . . . . . . 6
4.6. Distinguishing parallel links . . . . . . . . . . . . . . 7 4.6. Distinguishing parallel links . . . . . . . . . . . . . . 7
5. Elements of procedure . . . . . . . . . . . . . . . . . . . . 8 5. Elements of procedure . . . . . . . . . . . . . . . . . . . . 8
5.1. Point-to-point links . . . . . . . . . . . . . . . . . . 8 5.1. Point-to-point links . . . . . . . . . . . . . . . . . . 8
5.2. Broadcast/NBMA links . . . . . . . . . . . . . . . . . . 8 5.2. Broadcast/NBMA links . . . . . . . . . . . . . . . . . . 9
5.3. Point-to-multipoint links . . . . . . . . . . . . . . . . 9 5.3. Point-to-multipoint links . . . . . . . . . . . . . . . . 9
5.4. Unnumbered interfaces . . . . . . . . . . . . . . . . . . 9 5.4. Unnumbered interfaces . . . . . . . . . . . . . . . . . . 9
5.5. Hybrid Broadcast and P2MP interfaces . . . . . . . . . . 9 5.5. Hybrid Broadcast and P2MP interfaces . . . . . . . . . . 10
6. Backward compatibility . . . . . . . . . . . . . . . . . . . 10 6. Backward compatibility . . . . . . . . . . . . . . . . . . . 10
7. Applications . . . . . . . . . . . . . . . . . . . . . . . . 10 7. Applications . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Pseudowire Services . . . . . . . . . . . . . . . . . . . 10 7.1. Pseudowire Services . . . . . . . . . . . . . . . . . . . 10
7.2. Controller based Traffic Engineering Deployments . . . . 11 7.2. Controller based Traffic Engineering Deployments . . . . 11
7.3. L3VPN Services and sham-links . . . . . . . . . . . . . . 12 7.3. L3VPN Services and sham-links . . . . . . . . . . . . . . 12
7.4. Hub and spoke deployment . . . . . . . . . . . . . . . . 13 7.4. Hub and spoke deployment . . . . . . . . . . . . . . . . 13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 13 8. Security Considerations . . . . . . . . . . . . . . . . . . . 13
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
11.1. Normative References . . . . . . . . . . . . . . . . . . 14 11.1. Normative References . . . . . . . . . . . . . . . . . . 14
11.2. Informative References . . . . . . . . . . . . . . . . . 14 11.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction 1. Introduction
When a node is being prepared for a planned maintenance or upgrade, When a node is being prepared for a planned maintenance or upgrade,
[RFC6987] provides mechanisms to advertise the node being in an [RFC6987] provides mechanisms to advertise the node being in a
overload state by setting all outgoing link costs to MaxLinkMetric graceful-shutdown state by setting all outgoing link costs to
(0xffff). These procedures are specific to the maintenance activity MaxLinkMetric (0xffff). These procedures are specific to the
on a node and cannot be used when a single link on the node requires maintenance activity on a node and cannot be used when a single link
maintenance. on the node requires maintenance.
In traffic-engineering deployments, LSPs need to be diverted from the In traffic-engineering deployments, LSPs need to be diverted from the
link without disrupting the services. [RFC5817] describes link without disrupting the services. [RFC5817] describes
requirements and procedures for graceful shutdown of MPLS links. It requirements and procedures for graceful shutdown of MPLS links. It
is useful to be able to advertise the impending maintenance activity is useful to be able to advertise the impending maintenance activity
on the link and to have LSP re-routing policies at the ingress to on the link and to have LSP re-routing policies at the ingress to
route the LSPs away from the link. route the LSPs away from the link.
Many OSPFv2 or OSPFv3 deployments run on overlay networks provisioned Many OSPFv2 or OSPFv3 deployments run on overlay networks provisioned
by means of pseudo-wires or L2-circuits. Prior to devices in the by means of pseudo-wires or L2-circuits. Prior to devices in the
underlying network going offline for maintenance, it is useful to underlying network going offline for maintenance, it is useful to
divert the traffic away from the node before the maintenance is divert the traffic away from the node before the maintenance is
actually performed. Since the nodes in the underlying network are actually performed. Since the nodes in the underlying network are
not visible to OSPF, the existing stub router mechanism described in not visible to OSPF, the existing stub router mechanism described in
[RFC6987] cannot be used. An application specific to this use case [RFC6987] cannot be used. An application specific to this use case
is described in Section 7.1. is described in Section 7.1.
This document provides mechanisms to advertise link-overload state in The procedures described in this draft may be used to divert the
the flexible encodings provided by OSPFv2 Prefix/Link Attribute traffic away from the link in other scenarios and is not restricted
Advertisement [RFC7684]. Throughout this document, OSPF is used when to link-shutdown or link-replacement activity.
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. This document provides mechanisms to advertise graceful-link-shutdown
state in the flexible encodings provided by OSPFv2 Prefix/Link
Attribute Advertisement [RFC7684]. 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.
2. Motivation 2. Motivation
The motivation of this document is to reduce manual intervention The motivation of this document is to reduce manual intervention
during maintenance activities. The following objectives help to during maintenance activities. The following objectives help to
accomplish this in a range of deployment scenarios. accomplish this in a range of deployment scenarios.
1. Advertise impending maintenance activity so that traffic from 1. Advertise impending maintenance activity so that traffic from
both directions can be diverted away from the link. both directions can be diverted away from the link.
2. Allow the solution to be backward compatible so that nodes that 2. Allow the solution to be backward compatible so that nodes that
do not understand the new advertisement do not cause routing do not understand the new advertisement do not cause routing
loops. loops.
3. Advertise the maintenance activity to other nodes in the network 3. Advertise the maintenance activity to other nodes in the network
so that LSP ingress routers/controllers can learn of the so that LSP ingress routers/controllers can learn about the
impending maintenance activity and apply specific policies to re- impending maintenance activity and apply specific policies to re-
route the LSPs for traffic-engineering based deployments. route the LSPs for traffic-engineering based deployments.
4. Allow the link to be used as last resort link to prevent traffic 4. Allow the link to be used as last resort link to prevent traffic
disruption when alternate paths are not available. disruption when alternate paths are not available.
3. Flooding Scope 3. Flooding Scope
The link-overload information is flooded in area-scoped Extended Link The graceful-link-shutdown information is flooded in area-scoped
Opaque LSA [RFC7684]. The Link-Overload sub-TLV MAY be processed by Extended Link Opaque LSA [RFC7684]. The Graceful-Link-Shutdown sub-
the head-end nodes or the controller as described in the Section 7. TLV MAY be processed by the head-end nodes or the controller as
The procedures for processing the Link-Overload sub-TLV are described described in the Section 7. The procedures for processing the
in Section 5. Graceful-Link-Shutdown sub-TLV are described in Section 5.
4. Link-Overload sub-TLV 4. Graceful-Link-Shutdown sub-TLV
4.1. OSPFv2 Link-overload sub-TLV 4.1. OSPFv2 graceful-link-shutdown sub-TLV
The Link-Overload sub-TLV identifies the link as being in overload The Graceful-Link-Shutdown sub-TLV identifies the link as being
state.It is advertised in extended Link TLV of the Extended Link gracefully shutdown. It is advertised in extended Link TLV of the
Opaque LSA as defined in [RFC7684]. Extended Link Opaque LSA as defined in [RFC7684].
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Link-Overload sub-TLV for OSPFv2 Figure 1: Graceful-Link-Shutdown sub-TLV for OSPFv2
Type : TBA (suggested value 7) Type : TBA (suggested value 7)
Length: 0 Length: 0
4.2. Remote IPv4 Address Sub-TLV 4.2. Remote IPv4 Address Sub-TLV
This sub-TLV specifies the IPv4 address of remote endpoint on the This sub-TLV specifies the IPv4 address of remote endpoint on the
link. It is advertised in the Extended Link TLV as defined in link. It is advertised in the Extended Link TLV as defined in
[RFC7684]. This sub-TLV is optional and MAY be advertised in area- [RFC7684]. This sub-TLV is optional and MAY be advertised in area-
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Figure 3: Local/Remote Interface ID Sub-TLV Figure 3: Local/Remote Interface ID Sub-TLV
Type : TBA (suggested value 9) Type : TBA (suggested value 9)
Length: 8 Length: 8
Value: 4 octets of Local Interface ID followed by 4 octets of Remote Value: 4 octets of Local Interface ID followed by 4 octets of Remote
interface ID. interface ID.
4.4. OSPFv3 Link-Overload sub-TLV 4.4. OSPFv3 Graceful-Link-Shutdown sub-TLV
The Link Overload sub-TLV is carried in the Router-Link TLV as The Graceful-Link-Shutdown sub-TLV is carried in the Router-Link TLV
defined in the [I-D.ietf-ospf-ospfv3-lsa-extend] for OSPFv3. The as defined in the [I-D.ietf-ospf-ospfv3-lsa-extend] for OSPFv3. The
Router-Link TLV contains the neighbour interface-id and can uniquely Router-Link TLV contains the neighbour interface-id and can uniquely
identify the link on the remote node. identify the link on the remote node.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Link-Overload sub-TLV for OSPFv3 Figure 4: Graceful-Link-Shutdown sub-TLV for OSPFv3
Type : TBA (Suggested value 7) Type : TBA (Suggested value 7)
Length: 0 Length: 0
4.5. BGP-LS Link-overload TLV 4.5. BGP-LS Graceful-Link-Shutdown TLV
BGP-LS as defined in [RFC7752] is a mechanism to distribute network BGP-LS as defined in [RFC7752] is a mechanism to distribute network
information to external entities using BGP routing protocol. link- information to external entities using BGP routing protocol.
overload is an imporatant link information that the external entities Graceful-link-shutdown is an imporatant link information that the
can use for various usecases as defined in Section 7. BGP Link NLRI external entities can use for various use cases as defined in
is used to carry the link information. a new TLV called Link- Section 7. BGP Link NLRI is used to carry the link information. A
Overload is defined to describe the link attribute corresponding to new TLV called Graceful-Link-Shutdown is defined to describe the link
link-overload state. attribute corresponding to graceful-link-shutdown state.
4.6. Distinguishing parallel links 4.6. Distinguishing parallel links
++++++++++I.w I.y +++++++++ ++++++++++I.w I.y +++++++++
|Router A|------------------|Router B | |Router A|------------------|Router B |
| |------------------| | | |------------------| |
++++++++++I.x I.z++++++++++ ++++++++++I.x I.z++++++++++
Figure 5: Parallel Linkls Figure 5: Parallel Linkls
skipping to change at page 7, line 35 skipping to change at page 7, line 35
Link-ID: Router-ID B Link-ID: Router-ID B
Link-Data = I.w Link-Data = I.w
A third node (controller or head-end) in the network cannot A third node (controller or head-end) in the network cannot
distinguish the Interface on router B which is connected to this distinguish the Interface on router B which is connected to this
particular Interface with the above information. Interface with particular Interface with the above information. Interface with
address I.y or I.z could be chosen due to this ambiguity. In such address I.y or I.z could be chosen due to this ambiguity. In such
cases Remote-IPv4 Address sub-TLV should be originated and added to cases Remote-IPv4 Address sub-TLV should be originated and added to
the extended link-TLV. The usecases as described in Section 7 the extended link-TLV. The use cases as described in Section 7
require controller or head-end nodes to interpret the link-overload require controller or head-end nodes to interpret the graceful-link-
information and hence the need for the RemoteIPv4 address sub-TLV. shutdown information and hence the need for the RemoteIPv4 address
I.y is carried in the extended-link-TLV which unambiguously sub-TLV. I.y is carried in the extended-link-TLV which unambiguously
identifies the interface on the remote side. OSPFv3 Router-link-TLV identifies the interface on the remote side. OSPFv3 Router-link-TLV
as described in [I-D.ietf-ospf-ospfv3-lsa-extend] contains Interface as described in [I-D.ietf-ospf-ospfv3-lsa-extend] contains Interface
ID and neighbor's Interface-ID which can uniquely identify connecting ID and neighbor's Interface-ID which can uniquely identify connecting
interface on the remote side and hence OSPFv3 does not require interface on the remote side and hence OSPFv3 does not require
seperate Remote-IPv6 address to be advertised along with OSPFv2-link- seperate Remote-IPv6 address to be advertised along with OSPFv3-
overload-sub-TLV. Graceful-Link-Shutdown sub-TLV.
5. Elements of procedure 5. Elements of procedure
As defined in [RFC7684] every link on the node will have a separate As defined in [RFC7684] every link on the node will have a separate
Extended Link Opaque LSA. The node that has the link to be taken out Extended Link Opaque LSA. The node that has the link to be taken out
of service SHOULD advertise the Link-Overload sub-TLV in the Extended of service SHOULD advertise the Graceful-Link-Shutdown sub-TLV in the
Link TLV of the Extended Link Opaque LSA as defined in [RFC7684] for Extended Link TLV of the Extended Link Opaque LSA as defined in
OSPFv2. The Link-Overload sub-TLV indicates that the link identified [RFC7684] for OSPFv2. The Graceful-Link-Shutdown sub-TLV indicates
by the sub-TLV is overloaded. The Link-Overload information is that the link identified by the sub-TLV is subjected to maintenance.
advertised as a property of the link and is flooded across the area. The Graceful-Link-Shutdown information is advertised as a property of
This information can be used by ingress routers or controllers to the link and is flooded across the area. This information can be
take special actions. An application specific to this use case is used by ingress routers or controllers to take special actions. An
described in Section 7.2. application specific to this use case is described in Section 7.2.
The precise action taken by the remote node at the other end of the The precise action taken by the remote node at the other end of the
link identified as overloaded depends on the link type. link identified for graceful-shutdown depends on the link type.
5.1. Point-to-point links 5.1. Point-to-point links
The node that has the link to be taken out of service MUST set metric The node that has the link to be taken out of service MUST set metric
of the link to MaxLinkMetric (0xffff) and re-originate its router- of the link to MaxLinkMetric (0xffff) and re-originate its router-
LSA. The TE metric SHOULD be set to MAX-TE-METRIC (0xfffffffe) and LSA. MAX-TE-METRIC is a constant defined by this draft and set to
the node SHOULD re-originate the corresponding TE Link Opaque LSAs. 0xfffffffe. The TE metric SHOULD be set to MAX-TE-METRIC
When a Link-Overload sub-TLV is received for a point-to-point link, (0xfffffffe) and the node SHOULD re-originate the corresponding TE
the remote node MUST identify the local link which corresponds to the Link Opaque LSAs. When a Graceful-Link-Shutdown sub-TLV is received
overloaded link and set the metric to MaxLinkMetric (0xffff)and the for a point-to-point link, the remote node MUST identify the local
remote node MUST re-originate its router-LSA with the changed metric. link which corresponds to the graceful-shutdown link and set the
The TE metric SHOULD be set to MAX-TE-METRIC (0xfffffffe) and the TE metric to MaxLinkMetric (0xffff) and the remote node MUST re-
opaque LSA for the link SHOULD be re-originated with new value. originate its router-LSA with the changed metric. The TE metric
SHOULD be set to MAX-TE-METRIC (0xfffffffe) and the TE opaque LSA for
the link SHOULD be re-originated with new value.
The Extended link opaque LSAs and the Extended link TLV are not The Extended link opaque LSAs and the Extended link TLV are not
scoped for multi-topology [RFC4915]. In multi-topology deployments scoped for multi-topology [RFC4915]. In multi-topology deployments
[RFC4915], the Link-Overload sub-TLV advertised in an Extended Link [RFC4915], the Graceful-Link-Shutdown sub-TLV advertised in an
opaque LSA corresponds to all the topologies which include the link. Extended Link opaque LSA corresponds to all the topologies which
The receiver node SHOULD change the metric in the reverse direction include the link. The receiver node SHOULD change the metric in the
for all the topologies which include the remote link and re-originate reverse direction for all the topologies which include the remote
the router-LSA as defined in [RFC4915]. link and re-originate the router-LSA as defined in [RFC4915].
When the originator of the Link-Overload sub-TLV purges the Extended When the originator of the Graceful-Link-Shutdown sub-TLV purges the
Link Opaque LSA or re-originates it without the Link-Overload sub- Extended Link Opaque LSA or re-originates it without the Graceful-
TLV, the remote node must re-originate the appropriate LSAs with the Link-Shutdown sub-TLV, the remote node must re-originate the
metric and TE metric values set to their original values. appropriate LSAs with the metric and TE metric values set to their
original values.
5.2. Broadcast/NBMA links 5.2. Broadcast/NBMA links
Broadcast or NBMA networks in OSPF are represented by a star topology Broadcast or NBMA networks in OSPF are represented by a star topology
where the Designated Router (DR) is the central point to which all where the Designated Router (DR) is the central point to which all
other routers on the broadcast or NBMA network logically connect. As other routers on the broadcast or NBMA network logically connect. As
a result, routers on the broadcast or NBMA network advertise only a result, routers on the broadcast or NBMA network advertise only
their adjacency to the DR. Routers that do not act as DR do not form their adjacency to the DR. Routers that do not act as DR do not form
or advertise adjacencies with each other. For the Broadcast links, or advertise adjacencies with each other. For the Broadcast links,
the MaxLinkMetric on the remote link cannot be changed since all the the MaxLinkMetric on the remote link cannot be changed since all the
neighbors are on same link. Setting the link cost to MaxLinkMetric neighbors are on same link. Setting the link cost to MaxLinkMetric
would impact paths going via all neighbors. would impact paths going via all neighbors.
The node that has the link to be taken out of service MUST set metric The node that has the link to be taken out of service MUST set metric
of the link to MaxLinkMetric (0xffff) and re-originate the Router- of the link to MaxLinkMetric (0xffff) and re-originate the Router-
LSA. The TE metric SHOULD be set to MAX-TE-METRIC( 0xfffffffe) and LSA. The TE metric SHOULD be set to MAX-TE-METRIC( 0xfffffffe) and
the node SHOULD re-originate the corresponding TE Link Opaque LSAs. the node SHOULD re-originate the corresponding TE Link Opaque LSAs.
For a broadcast link, the two part metric as described in [RFC8042] For a broadcast link, the two part metric as described in [RFC8042]
is used. The node originating the Link-Overload sub-TLV MUST set the is used. The node originating the Graceful-Link-Shutdown sub-TLV
metric in the Network-to-Router Metric sub-TLV to MaxLinkMetric MUST set the metric in the Network-to-Router Metric sub-TLV to
(0xffff) for OSPFv2 and OSPFv3 and re-originate the corresponding MaxLinkMetric (0xffff) for OSPFv2 and OSPFv3 and re-originate the
LSAs. The nodes that receive the two-part metric should follow the corresponding LSAs. The nodes that receive the two-part metric
procedures described in [RFC8042]. The backward compatibility should follow the procedures described in [RFC8042]. The backward
procedures described in [RFC8042] should be followed to ensure loop compatibility procedures described in [RFC8042] should be followed to
free routing. ensure loop free routing.
5.3. Point-to-multipoint links 5.3. Point-to-multipoint links
Operation for the point-to-multipoint links is similar to the point- Operation for the point-to-multipoint links is similar to the point-
to-point links. When a Link-Overload sub-TLV is received for a to-point links. When a Graceful-Link-Shutdown sub-TLV is received
point-to-multipoint link the remote node MUST identify the neighbour for a point-to-multipoint link the remote node MUST identify the
which corresponds to the overloaded link and set the metric to neighbour which corresponds to the graceful-shutdown link and set the
MaxLinkMetric (0xffff). The remote node MUST re-originate the metric to MaxLinkMetric (0xffff). The remote node MUST re-originate
router-LSA with the changed metric for the correponding neighbor. the router-LSA with the changed metric for the correponding neighbor.
5.4. Unnumbered interfaces 5.4. Unnumbered interfaces
Unnumbered interface do not have a unique IP address and borrow their Unnumbered interface do not have a unique IP address and borrow their
address from other interfaces. [RFC2328] describes procedures to address from other interfaces. [RFC2328] describes procedures to
handle unnumbered interfaces in the context of the router-LSA. We handle unnumbered interfaces in the context of the router-LSA. We
apply a similar procedure to the Extended Link TLV advertising the apply a similar procedure to the Extended Link TLV advertising the
Link-Overload sub-TLV in order to handle unnumbered interfaces. The Graceful-Link-Shutdown sub-TLV in order to handle unnumbered
link-data field in the Extended Link TLV includes the Local interfaces. The link-data field in the Extended Link TLV includes
interface-id instead of the IP address. The Local/Remote Interface the Local interface-id instead of the IP address. The Local/Remote
ID sub-TLV MUST be advertised when there are multiple parallel Interface ID sub-TLV MUST be advertised when there are multiple
unnumbered interfaces between two nodes. One of the mechanisms to parallel unnumbered interfaces between two nodes. One of the
obtain the interface-id of the remote side are defined in [RFC4203]. mechanisms to obtain the interface-id of the remote side are defined
in [RFC4203].
5.5. Hybrid Broadcast and P2MP interfaces 5.5. Hybrid Broadcast and P2MP interfaces
Hybrid Broadcast and P2MP interfaces represent a broadcast network Hybrid Broadcast and P2MP interfaces represent a broadcast network
modeled as P2MP interfaces. [RFC6845] describes procedures to handle modeled as P2MP interfaces. [RFC6845] describes procedures to handle
these interfaces. Operation for the Hybrid interfaces is similar to these interfaces. Operation for the Hybrid interfaces is similar to
the P2MP interfaces. When a Link-Overload sub-TLV is received for a the P2MP interfaces. When a Graceful-Link-Shutdown sub-TLV is
hybrid link, the remote node MUST identify the neighbor which received for a hybrid link, the remote node MUST identify the
corresponds to the overloaded link and set the metric to neighbor which corresponds to the graceful-shutdown link and set the
MaxLinkMetric (0xffff). All the remote nodes connected to originator metric to MaxLinkMetric (0xffff). All the remote nodes connected to
MUST re-originate the router-LSA with the changed metric for the originator MUST re-originate the router-LSA with the changed metric
neighbor. for the neighbor.
6. Backward compatibility 6. Backward compatibility
The mechanisms described in the document are fully backward The mechanisms described in the document are fully backward
compatible. It is required that the node adverting the Link-Overload compatible. It is required that the node adverting the Graceful-
sub-TLV as well as the node at the remote end of the overloaded link Link-Shutdown sub-TLV as well as the node at the remote end of the
support the extensions described herein for the traffic to diverted graceful-shutdown link support the extensions described herein for
from the overloaded link. If the remote node doesn't support the the traffic to diverted from the graceful-shutdown link. If the
capability, it will still use the overloaded link but there are no remote node doesn't support the capability, it will still use the
other adverse effects. In the case of broadcast links using two-part graceful-shutdown link but there are no other adverse effects. In
metrics, the backward compatibility procedures as described in the case of broadcast links using two-part metrics, the backward
[RFC8042] are applicable. compatibility procedures as described in [RFC8042] are applicable.
7. Applications 7. Applications
7.1. Pseudowire Services 7.1. Pseudowire Services
Many service providers offer pseudo-wire services to customers using Many service providers offer pseudo-wire services to customers using
L2 circuits. The IGP protocol that runs in the customer network L2 circuits. The IGP protocol that runs in the customer network
would also run over the pseudo-wire to create a seamless private would also run over the pseudo-wire to create a seamless private
network for the customer. Service providers want to offer overload network for the customer. Service providers want to offer graceful-
functionality when the PE device is taken-out for maintenance. The shutdown functionality when the PE device is taken-out for
provider should guarantee that the PE is taken out for maintenance maintenance. The provider should guarantee that the PE is taken out
only after the service is successfully diverted on an alternate path. for maintenance only after the service is successfully diverted on an
There can be large number of customers attached to a PE node and the alternate path. There can be large number of customers attached to a
remote end-points for these pseudo-wires are spread across the PE node and the remote end-points for these pseudo-wires are spread
service provider's network. It is a tedious and error-prone process across the service provider's network. It is a tedious and error-
to change the metric for all pseudo-wires in both directions. The prone process to change the metric for all pseudo-wires in both
link-overload feature simplifies the process by increasing the metric directions. The graceful-link-shutdown feature simplifies the
on the link in the reverse direction as well so that traffic in both process by increasing the metric on the link in the reverse direction
directions is diverted away from the PE undergoing maintenance. The as well so that traffic in both directions is diverted away from the
Link-Overload feature allows the link to be used as a last resort PE undergoing maintenance. The Graceful-Link-Shutdown feature allows
link so that traffic is not disrupted when alternative paths are not the link to be used as a last resort link so that traffic is not
available. disrupted when alternative paths are not available.
Private VLAN Private VLAN
======================================= =======================================
| | | |
| | | |
| ------PE3---------------PE4------CE3 | ------PE3---------------PE4------CE3
| / \ | / \
| / \ | / \
CE1---------PE1----------PE2---------CE2 CE1---------PE1----------PE2---------CE2
| \ | \
skipping to change at page 11, line 25 skipping to change at page 11, line 25
| ------CE4 | ------CE4
| | | |
| | | |
| | | |
================================= =================================
Private VLAN Private VLAN
Figure 6: Pseudowire Services Figure 6: Pseudowire Services
In the example shown in Figure 6, when the PE1 node is going out of In the example shown in Figure 6, when the PE1 node is going out of
service for maintenance, service providers set the PE1 to overload service for maintenance, service providers set the PE1 to graceful-
state. The PE1 going in to overload state triggers all the CEs link-shutdown state. The PE1 going in to maintenance state triggers
connected to the PE (CE1 in this case) to set their pseudowire links all the CEs connected to the PE (CE1 in this case) to set their
passing via PE1 to link-overload state. The mechanisms used to pseudowire links passing via PE1 to graceful-link-shutdown state.
communicate between PE1 and CE1 is outside the scope of this The mechanisms used to communicate between PE1 and CE1 is outside the
document. CE1 sets the link-overload state on its private VLAN scope of this document. CE1 sets the graceful-link-shutdown state on
connecting CE3, CE2 and CE4 and changes the metric to MAX_METRIC and its private VLAN connecting CE3, CE2 and CE4 and changes the metric
re-originates the corresponding LSA. The remote end of the link at to MAX_METRIC and re-originates the corresponding LSA. The remote
CE3, CE2, and CE4 also set the metric on the link to MaxLinkMetric end of the link at CE3, CE2, and CE4 also set the metric on the link
and the traffic from both directions gets diverted away from the to MaxLinkMetric and the traffic from both directions gets diverted
pseudowires. away from the pseudowires.
7.2. Controller based Traffic Engineering Deployments 7.2. Controller based Traffic Engineering Deployments
In controller-based deployments where the controller participates in In controller-based deployments where the controller participates in
the IGP protocol, the controller can also receive the link-overload the IGP protocol, the controller can also receive the graceful-link-
information as a warning that link maintenance is imminent. Using shutdown information as a warning that link maintenance is imminent.
this information, the controller can find alternate paths for traffic Using this information, the controller can find alternate paths for
which uses the affected link. The controller can apply various traffic which uses the affected link. The controller can apply
policies and re-route the LSPs away from the link undergoing various policies and re-route the LSPs away from the link undergoing
maintenance. If there are no alternate paths satisfying the traffic maintenance. If there are no alternate paths satisfying the traffic
engineering constraints, the controller might temporarily relax those engineering constraints, the controller might temporarily relax those
constraints and put the service on a different path. Increasing the constraints and put the service on a different path. Increasing the
link metric alone does not specify the maintenance activity as the link metric alone does not specify the maintenance activity as the
metric could increase in events such as LDP-IGP synchronisation. An metric could increase in events such as LDP-IGP synchronisation. An
explicit indication from the router using the link-overload sub-TLV explicit indication from the router using the graceful-link-shutdown
is needed to inform the Controller or head-end routers. sub-TLV is needed to inform the Controller or head-end routers.
_____________ _____________
| | | |
-------------| Controller |-------------- -------------| Controller |--------------
| |____________ | | | |____________ | |
| | | |
|--------- Primary Path ------------------| |--------- Primary Path ------------------|
PE1---------P1----------------P2---------PE2 PE1---------P1----------------P2---------PE2
| | | |
| | | |
|________P3________| |________P3________|
Alternate Path Alternate Path
Figure 7: Controller based Traffic Engineering Figure 7: Controller based Traffic Engineering
In the above example, PE1->PE2 LSP is set-up to satisfy a constraint In the above example, PE1->PE2 LSP is set-up to satisfy a constraint
of 10 Gbps bandwidth on each link. The links P1->P3 and P3->P2 have of 10 Gbps bandwidth on each link. The links P1->P3 and P3->P2 have
only 1 Gbps capacity and there is no alternate path satisfying the only 1 Gbps capacity and there is no alternate path satisfying the
bandwidth constraint of 10Gbps. When P1->P2 link is being prepared bandwidth constraint of 10Gbps. When P1->P2 link is being prepared
for maintenance, the controller receives the link-overload for maintenance, the controller receives the graceful-link-shutdown
information, as there is no alternate path available which satisfies information, as there is no alternate path available which satisfies
the constraints, the controller chooses a path that is less optimal the constraints, the controller chooses a path that is less optimal
and temporarily sets up an alternate path via P1->P3->P2. Once the 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 traffic is diverted, the P1->P2 link can be taken out of service for
maintenance/upgrade. maintenance/upgrade.
7.3. L3VPN Services and sham-links 7.3. L3VPN Services and sham-links
Many service providers offer L3VPN services to customers and CE-PE Many service providers offer L3VPN services to customers and CE-PE
links run OSPF [RFC4577]. When PE is taken out of service for links run OSPF [RFC4577]. When PE is taken out of service for
maintenance, all the links on the PE can be set to link-overload maintenance, all the links on the PE can be set to graceful-link-
state which will gurantee that the traffic to/from dual-homed CEs shutdown state which will gurantee that the traffic to/from dual-
gets diverted. The interaction between OSPF and BGP is outside the homed CEs gets diverted. The interaction between OSPF and BGP is
scope of this document. [RFC6987] based mechanism with summaries and outside the scope of this document. [RFC6987] based mechanism with
externals advertised with high metrics could also be used to achieve summaries and externals advertised with high metrics could also be
the same functionality when implementations support high metrics used to achieve the same functionality when implementations support
advertisement for summaries and externals. high metrics advertisement for summaries and externals.
Another useful usecase is when ISPs provide sham-link services to Another useful usecase is when ISPs provide sham-link services to
customers [RFC4577]. When PE goes out of service for maintenance, customers [RFC4577]. When PE goes out of service for maintenance,
all sham-links on the PE can be set to link-overload state and all sham-links on the PE can be set to graceful-link-shutdown state
traffic can be divered from both ends without having to touch the and traffic can be divered from both ends without having to touch the
configurations on the remote end of the sham-links. configurations on the remote end of the sham-links.
7.4. Hub and spoke deployment 7.4. Hub and spoke deployment
OSPF is largely deployed in Hub and Spoke deployments with a large OSPF is largely deployed in Hub and Spoke deployments with a large
number of spokes connecting to the Hub. It is a general practice to number of spokes connecting to the Hub. It is a general practice to
deploy multiple Hubs with all spokes connecting to these Hubs to deploy multiple Hubs with all spokes connecting to these Hubs to
achieve redundancy. The [RFC6987] mechanism can be used to divert achieve redundancy. The [RFC6987] mechanism can be used to divert
the spoke-to-spoke traffic from the overloaded hub router. The the spoke-to-spoke traffic from the overloaded hub router. The
traffic that flows from spokes via the hub into an external network traffic that flows from spokes via the hub into an external network
may not be diverted in certain scenarios.When a Hub node goes down may not be diverted in certain scenarios.When a Hub node goes down
for maintenance, all links on the Hub can be set to link-overload for maintenance, all links on the Hub can be set to graceful-link-
state and traffic gets divered from the spoke sites as well without shutdown state and traffic gets divered from the spoke sites as well
having to make configuration changes on the spokes. without having to make configuration changes on the spokes.
8. Security Considerations 8. Security Considerations
This document does not introduce any further security issues other This document does not introduce any further security issues other
than those discussed in [RFC2328] and [RFC5340]. than those discussed in [RFC2328] and [RFC5340].
9. IANA Considerations 9. IANA Considerations
This specification updates one OSPF registry: This specification updates one OSPF registry:
OSPFv2 Extended Link TLV Sub-TLVs OSPFv2 Extended Link TLV Sub-TLVs
i) Link-Overload Sub-TLV - Suggested value 7 i) Graceful-Link-Shutdown Sub-TLV - Suggested value 7
ii) Remote IPv4 Address Sub-TLV - Suggested value 8 ii) Remote IPv4 Address Sub-TLV - Suggested value 8
iii) Local/Remote Interface ID Sub-TLV - Suggested Value 9 iii) Local/Remote Interface ID Sub-TLV - Suggested Value 9
OSPFv3 Extended-LSA sub-TLV Registry OSPFv3 Extended-LSA sub-TLV Registry
i) Link-Overload sub-TLV - suggested value 7 i) Graceful-Link-Shutdown sub-TLV - suggested value 7
BGP-LS Link NLRI Registry [RFC7752] BGP-LS Link NLRI Registry [RFC7752]
i)Link-Overload TLV - Suggested 1101 i)Graceful-Link-Shutdown TLV - Suggested 1101
10. Acknowledgements 10. Acknowledgements
Thanks to Chris Bowers for valuable inputs and edits to the document. Thanks to Chris Bowers for valuable inputs and edits to the document.
Thanks to Jeffrey Zhang, Acee Lindem and Ketan Talaulikar for inputs. Thanks to Jeffrey Zhang, Acee Lindem and Ketan Talaulikar for inputs.
Thanks to Karsten Thomann for careful review and inputs on the Thanks to Karsten Thomann for careful review and inputs on the
applications where link-overload is useful. applications where graceful-link-shutdown is useful.
11. References 11. References
11.1. Normative References 11.1. Normative References
[I-D.ietf-ospf-ospfv3-lsa-extend] [I-D.ietf-ospf-ospfv3-lsa-extend]
Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3 Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3
LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-10 LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-10
(work in progress), May 2016. (work in progress), May 2016.
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