draft-ietf-ospf-link-overload-08.txt   draft-ietf-ospf-link-overload-09.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: January 18, 2018 H. Gredler Expires: February 15, 2018 H. Gredler
Individual Individual
M. Nanduri M. Nanduri
ebay Corporation ebay Corporation
L. Jalil L. Jalil
Verizon Verizon
July 17, 2017 August 14, 2017
OSPF Link Overload OSPF Link Overload
draft-ietf-ospf-link-overload-08 draft-ietf-ospf-link-overload-09
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 metric on one side of the link is not
sufficient to divert the traffic flowing in the other direction. sufficient 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 being in an overload state to indicate able to advertise a link being in an overload state to indicate
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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 http://datatracker.ietf.org/drafts/current/. Drafts is at http://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 January 18, 2018. This Internet-Draft will expire on February 15, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 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
(http://trustee.ietf.org/license-info) in effect on the date of (http://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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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. Link-Overload sub-TLV . . . . . . . . . . . . . . . . . . . . 4
4.1. OSPFv2 Link-overload sub-TLV . . . . . . . . . . . . . . 4 4.1. OSPFv2 Link-overload sub-TLV . . . . . . . . . . . . . . 4
4.2. Remote IPv4 address sub-TLV . . . . . . . . . . . . . . . 4 4.2. Remote IPv4 address sub-TLV . . . . . . . . . . . . . . . 4
4.3. Local/Remote Interface ID . . . . . . . . . . . . . . . . 5 4.3. Local/Remote Interface ID sub-TLV . . . . . . . . . . . . 5
4.4. OSPFv3 Link-Overload sub-TLV . . . . . . . . . . . . . . 6 4.4. OSPFv3 Link-Overload sub-TLV . . . . . . . . . . . . . . 6
5. Elements of procedure . . . . . . . . . . . . . . . . . . . . 6 5. Elements of procedure . . . . . . . . . . . . . . . . . . . . 6
5.1. Point-to-point links . . . . . . . . . . . . . . . . . . 6 5.1. Point-to-point links . . . . . . . . . . . . . . . . . . 6
5.2. Broadcast/NBMA links . . . . . . . . . . . . . . . . . . 7 5.2. Broadcast/NBMA links . . . . . . . . . . . . . . . . . . 7
5.3. Point-to-multipoint links . . . . . . . . . . . . . . . . 7 5.3. Point-to-multipoint links . . . . . . . . . . . . . . . . 7
5.4. Unnumbered interfaces . . . . . . . . . . . . . . . . . . 8 5.4. Unnumbered interfaces . . . . . . . . . . . . . . . . . . 8
5.5. Hybrid Broadcast and P2MP interfaces . . . . . . . . . . 8 5.5. Hybrid Broadcast and P2MP interfaces . . . . . . . . . . 8
6. Backward compatibility . . . . . . . . . . . . . . . . . . . 8 6. Backward compatibility . . . . . . . . . . . . . . . . . . . 8
7. Applications . . . . . . . . . . . . . . . . . . . . . . . . 8 7. Applications . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Pseudowire Services . . . . . . . . . . . . . . . . . . . 8 7.1. Pseudowire Services . . . . . . . . . . . . . . . . . . . 8
7.2. Controller based Traffic Engineering Deployments . . . . 9 7.2. Controller based Traffic Engineering Deployments . . . . 10
7.3. L3VPN Services and sham-links . . . . . . . . . . . . . . 10 7.3. L3VPN Services and sham-links . . . . . . . . . . . . . . 10
7.4. Hub and spoke deployment . . . . . . . . . . . . . . . . 11 7.4. Hub and spoke deployment . . . . . . . . . . . . . . . . 11
8. Security Considerations . . . . . . . . . . . . . . . . . . . 11 8. Security Considerations . . . . . . . . . . . . . . . . . . . 11
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
11.1. Normative References . . . . . . . . . . . . . . . . . . 12 11.1. Normative References . . . . . . . . . . . . . . . . . . 12
11.2. Informative References . . . . . . . . . . . . . . . . . 12 11.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
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 an
overload state by setting all outgoing link costs to MAX-METRIC overload state by setting all outgoing link costs to MAX-METRIC
(0xffff). These procedures are specific to the maintenance activity (0xffff). These procedures are specific to the maintenance activity
on a node and cannot be used when a single link attached to the node on a node and cannot be used when a single link on the node requires
requires maintenance. 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. It is useful to be able to link without disrupting the services. [RFC5817] describes
advertise the impending maintenance activity on the link and to have requirements and procedures for graceful shutdown of MPLS links. It
LSP re-routing policies at the ingress to route the LSPs away from is useful to be able to advertise the impending maintenance activity
the link. on the link and to have LSP re-routing policies at the ingress to
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 scheduled. Since the nodes in the underlying network are actually scheduled. 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 This document provides mechanisms to advertise link-overload state in
the flexible encodings provided by OSPFv2 Prefix/Link Attribute the flexible encodings provided by OSPFv2 Prefix/Link Attribute
Advertisement([RFC7684]). Throughout this document, OSPF is used Advertisement([RFC7684]). Throughout this document, OSPF is used
when the text applies to both OSPFv2 and OSPFv3. OSPFv2 or OSPFv3 is 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. 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
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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 link-overload information is flooded in area scoped Extended Link
Opaque LSA [RFC7684]. The Link-Overload sub-TLV MAY be processed by Opaque LSA [RFC7684]. The Link-Overload sub-TLV MAY be processed by
the head-end nodes or the controller as described in the Section 7. the head-end nodes or the controller as described in the Section 7.
The procedures for processing the Link-Overload sub-TLV is described The procedures for processing the Link-Overload sub-TLV are described
in Section 5. in Section 5.
4. Link-Overload sub-TLV 4. Link-Overload sub-TLV
4.1. OSPFv2 Link-overload sub-TLV 4.1. OSPFv2 Link-overload sub-TLV
The Link-Overload sub-TLV identifies the link being in overload The Link-Overload sub-TLV identifies the link being in overload
state. It is carried in extended Link TLV in the Extended Link state.It is carried in extended Link TLV in the Extended Link Opaque
Opaque LSA as defined in [RFC7684]. 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: Link-Overload sub-TLV for OSPFv2
Type : TBA (suggested value 5) Type : TBA (suggested value 5)
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 the link on remote side. This sub-TLV specifies the IPv4 address of remote endpoint on the
It is carried in extended Link TLV as defined in [RFC7684].This sub- link. It is advertised in extended Link TLV as defined in
TLV is optional and MAY be advertised in area scoped Extended Link [RFC7684].This sub-TLV is optional and MAY be advertised in area
Opaque LSA to identify the link when there are multiple parallel scoped Extended Link Opaque LSA to identify the link when there are
interfaces between two nodes. multiple parallel links between two nodes.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote IPv4 address | | Remote IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Remote IPv4 address sub-TLV Figure 2: Remote IPv4 address sub-TLV
Type : TBA (suggested value 4) Type : TBA (suggested value 4)
Length: 4 Length: 4
Value: Remote IPv4 address. The remote IP4 address is used to Value: Remote IPv4 address. The remote IP4 address is used to
identify the particular link when there are multiple parallel links identify the particular link when there are multiple parallel links
between two nodes. between two nodes.
4.3. Local/Remote Interface ID 4.3. Local/Remote Interface ID sub-TLV
This sub-TLV specifies local and remote interface identifiers. It is This sub-TLV specifies local and remote interface identifiers. It is
carried in extended Link TLV as defined in [RFC7684].This sub-TLV is advertised in extended Link TLV as defined in [RFC7684].This sub-TLV
optional and MAY be advertised in area scoped Extended Link Opaque is optional and MAY be advertised in area scoped Extended Link Opaque
LSA to identify the link when there are multiple parallel unnumbered LSA to identify the link when there are multiple parallel unnumbered
interfaces between two nodes. The local interface-id is generally links between two nodes. The local interface-id is generally readily
readily available. One of the mechanisms to obtain remote interface- available. One of the mechanisms to obtain remote interface-id is
id is described in [RFC4203]. described in [RFC4203].
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface ID | | Local Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Interface ID | | Remote Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type : TBA (suggested value 11) Type : TBA (suggested value 11)
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 Link-Overload sub-TLV
The definition of OSPFv3 Link-Overload sub-TLV is defined below. The The definition of OSPFv3 Link-Overload sub-TLV is defined below. The
area scope advertisement of Link-Overload sub-TLV for OSPFv3 will be area scoped advertisement of Link-Overload sub-TLV for OSPFv3 will be
described in a separate document. described in a separate document.
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: Link-Overload sub-TLV for OSPFv3
Type : TBA (Suggested value 4) Type : TBA (Suggested value 4)
Length: 0 Length: 0
5. Elements of procedure 5. Elements of procedure
The Link-Overload sub-TLV indicates that the link identified by the The Link-Overload sub-TLV indicates that the link identified by the
sub-TLV is overloaded. The node that has the link to be taken out of sub-TLV is overloaded. The node that has the link to be taken out of
service SHOULD originate the Link-Overload sub-TLV in the Extended service SHOULD advertise the Link-Overload sub-TLV in the Extended
Link TLV in the Extended Link Opaque LSA as defined in [RFC7684] for Link TLV in the Extended Link Opaque LSA as defined in [RFC7684] for
OSPFv2. The Link-Overload information is carried as a property of OSPFv2. The Link-Overload information is advertised as a property of
the link and is flooded across the area. This information can be the link and is flooded across the area. This information can be
used by ingress routers or controllers to take special actions. An used by ingress routers or controllers to take special actions. An
application specific to this use case is 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 as overloaded 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
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node SHOULD re-originate the TE Link Opaque LSAs. When a Link- node SHOULD re-originate the TE Link Opaque LSAs. When a Link-
Overload sub-TLV is received for a point-to-point link, the remote Overload sub-TLV is received for a point-to-point link, the remote
node MUST identify the local link which corresponds to the overloaded node MUST identify the local link which corresponds to the overloaded
link and set the metric to MAX-METRIC (0xffff)and the remote node link and set the metric to MAX-METRIC (0xffff)and the remote node
MUST re-originate the router-LSA with the changed metric. The TE MUST re-originate the router-LSA with the changed metric. The TE
metric SHOULD be set to MAX-TE-METRIC -1 (0xfffffffe) and the TE metric SHOULD be set to MAX-TE-METRIC -1 (0xfffffffe) and the TE
opaque LSA for the link SHOULD be re-originated with new value. opaque LSA for the link SHOULD be re-originated with new value.
Extended link opaque LSAs and the Extended link TLV are not scoped Extended link opaque LSAs and the Extended link TLV are not scoped
for multi-topology [RFC4915]. In multi-topology deployments for multi-topology [RFC4915]. In multi-topology deployments
[RFC4915], the Link-Overload sub-TLV carried in an Extended Link [RFC4915], the Link-Overload sub-TLV advertised in an Extended Link
opaque LSA corresponds to all the topologies the link belongs to. opaque LSA corresponds to all the topologies which include the link.
The receiver node SHOULD change the metric in the reverse direction The receiver node SHOULD change the metric in the reverse direction
corresponding to all the topologies to which the reverse link belongs for all the topologies which include the remote link and re-originate
and re-originate the Router LSA as defined in [RFC4915]. the Router LSA as defined in [RFC4915].
When the originator of the Link-Overload sub-TLV purges the Extended When the originator of the Link-Overload sub-TLV purges the Extended
Link Opaque LSA or re-originates it without the Link-Overload sub- Link Opaque LSA or re-originates it without the Link-Overload sub-
TLV, the remote node must re-originate the appropriate LSAs with the TLV, the remote node must re-originate the appropriate LSAs with the
metric and TE metric values set to their original values. 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
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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 MAX-METRIC on the remote link cannot be changed since all the the MAX-METRIC on the remote link cannot be changed since all the
neighbours are on same link. Setting the link cost to MAX-METRIC neighbours are on same link. Setting the link cost to MAX-METRIC
would impact paths going via all neighbours. would impact paths going via all neighbours.
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 MAX-METRIC(0xffff) and re-originate the Router-LSA. of the link to MAX-METRIC(0xffff) and re-originate the Router-LSA.
The TE metric SHOULD be set to MAX-TE-METRIC -1(0xfffffffe) and the The TE metric SHOULD be set to MAX-TE-METRIC -1(0xfffffffe) and the
node SHOULD re-originate the TE Link Opaque LSAs. For a broadcast node SHOULD re-originate the corresponding TE Link Opaque LSAs. For
link, the two part metric as described in [RFC8042] is used. The a broadcast link, the two part metric as described in [RFC8042] is
node originating the Link-Overload sub-TLV MUST set the metric in the used. The node originating the Link-Overload sub-TLV MUST set the
Network-to-Router Metric sub-TLV to MAX-METRIC 0xffff for OSPFv2 and metric in the Network-to-Router Metric sub-TLV to MAX-METRIC 0xffff
OSPFv3 and re-originate the LSAs the TLV is carried-in. The nodes for OSPFv2 and OSPFv3 and re-originate the corresponding LSAs. The
that receive the two part metric should follow the procedures nodes that receive the two part metric should follow the procedures
described in [RFC8042]. The backward compatibility procedures described in [RFC8042]. The backward compatibility procedures
described in [RFC8042] should be followed to ensure loop free described in [RFC8042] should be followed to ensure loop free
routing. 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 Link-Overload sub-TLV is received for a
point-to-multipoint link the remote node MUST identify the neighbour point-to-multipoint link the remote node MUST identify the neighbour
which corresponds to the overloaded link and set the metric to MAX- which corresponds to the overloaded link and set the metric to MAX-
METRIC (0xffff). The remote node MUST re-originate the Router-LSA METRIC (0xffff). The remote node MUST re-originate the Router-LSA
with the changed metric and flood into the OSPF area. with the changed metric.
5.4. Unnumbered interfaces 5.4. Unnumbered interfaces
Unnumbered interface do not have a unique IP addresses and borrow 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 carrying the Link- apply a similar procedure to the Extended Link TLV advertising the
Overload sub-TLV in to handle unnumbered interfaces. The link-data Link-Overload sub-TLV in to handle unnumbered interfaces. The link-
field in the Extended Link TLV carries the Local interface-id instead data field in the Extended Link TLV includes the Local interface-id
of the IP address. The Local/Remote Interface ID sub-TLV MUST be instead of the IP address. The Local/Remote Interface ID sub-TLV
originated when there are multiple parallel unnumbered interfaces MUST be advertised when there are multiple parallel unnumbered
between two nodes. One of the mechanisms to obtain interface-id of interfaces between two nodes. One of the mechanisms to obtain the
the remote side are defined in [RFC4203]. 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 Link-Overload sub-TLV is received for a
hybrid link the remote node MUST identify the neighbour which hybrid link the remote node MUST identify the neighbour which
corresponds to the overloaded link and set the metric to MAX-METRIC corresponds to the overloaded link and set the metric to MAX-METRIC
(0xffff). All the remote nodes connected to originator MUST re- (0xffff). All the remote nodes connected to originator MUST re-
originate the Router-LSA with the changed metric and flood into the originate the Router-LSA with the changed metric.
OSPF area.
6. Backward compatibility 6. Backward compatibility
The mechanism described in the document is fully backward compatible. The mechanisms described in the document are fully backward
It is required that the originator of the Link-Overload sub-TLV as compatible. It is required that the node adverting the Link-Overload
well as the node at the remote end of the link identified as sub-TLV as well as the node at the remote end of the overloaded link
overloaded understand the extensions defined in this document. In support the extensions described herein for the traffic to diverted
the case of broadcast links, the backward compatibility procedures as from the overloaded link. If the remote node doesn't support the
described in [RFC8042] are applicable. capability, it will still use the overloaded link but there are no
other adverse effects. In the case of broadcast links using two-part
metrics, the backward 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 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 overload
kind of functionality when the PE device is taken-out for functionality when the PE device is taken-out for maintenance. The
maintenance. The provider should guarantee that the PE is taken out provider should guarantee that the PE is taken out for maintenance
for maintenance only after the service is successfully diverted on an only after the service is successfully diverted on an alternate path.
alternate path. There can be large number of customers attached to a There can be large number of customers attached to a PE node and the
PE node and the remote end-points for these pseudo-wires are spread remote end-points for these pseudo-wires are spread across the
across the service provider's network. It is a tedious and error- service provider's network. It is a tedious and error-prone process
prone process to change the metric for all pseudo-wires in both to change the metric for all pseudo-wires in both directions. The
directions. The link-overload feature simplifies the process by link-overload feature simplifies the process by increasing the metric
increasing the metric on the link in the reverse direction as well so on the link in the reverse direction as well so that traffic in both
that traffic in both directions is diverted away from the PE directions is diverted away from the PE undergoing maintenance. The
undergoing maintenance. The Link-Overload feature allows the link to Link-Overload feature allows the link to be used as a last resort
be used as a last resort link so that traffic is not disrupted when link so that traffic is not disrupted when alternative paths are not
alternative paths are not available. available.
Private VLAN Private VLAN
======================================= =======================================
| | | |
| | | |
| ------PE3---------------PE4------CE3 | ------PE3---------------PE4------CE3
| / \ | / \
| / \ | / \
CE1---------PE1----------PE2---------CE2 CE1---------PE1----------PE2---------CE2
| \ | \
| \ | \
| ------CE4 | ------CE4
| | | |
| | | |
| | | |
================================= =================================
Private VLAN Private VLAN
Figure 5: Pseudowire Services Figure 5: Pseudowire Services
In the example shown in Figure 5, when the PE1 node is going for In the example shown in Figure 5, when the PE1 node is going out of
maintenance, service providers set the PE1 to overload state. The service for maintenance, service providers set the PE1 to overload
PE1 going in overload state triggers all the CEs (In this example state. The PE1 going in to overload state triggers all the CEs (In
CE1)connected to the PE to set their pseudowire links passing via PE1 this example CE1)connected to the PE to set their pseudowire links
to link-overload state. The mechanisms used to communicate between passing via PE1 to link-overload state. The mechanisms used to
PE1 and CE1 is outside the scope of this document. CE1 sets the communicate between PE1 and CE1 is outside the scope of this
link-overload state on its private VLAN connecting CE3, CE2 and CE4 document. CE1 sets the link-overload state on its private VLAN
and modifies the metric to MAX_METRIC and floods the information, the connecting CE3, CE2 and CE4 and changes the metric to MAX_METRIC and
remote end of the link at CE3, CE2, and CE4 also set the metric on re-originates the corresponding LSA. The remote end of the link at
the link to MAX-METRIC and the traffic from both directions gets CE3, CE2, and CE4 also set the metric on the link to MAX-METRIC and
diverted away from the link. the traffic from both directions gets diverted 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 link-overload
information as a warning that link maintenance is imminent. Using information as a warning that link maintenance is imminent. Using
this information, the controller can find alternate paths for traffic this information, the controller can find alternate paths for traffic
which use the affected link. The controller can apply various which uses the affected link. The controller can apply various
policies and re-route the LSPs away from the link undergoing 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 link-overload sub-TLV
is needed to inform the Controller or head-end routers. is needed to inform the Controller or head-end routers.
_____________ _____________
skipping to change at page 10, line 44 skipping to change at page 10, line 50
maintenance, the controller receives the link-overload information, maintenance, the controller receives the link-overload information,
as there is no alternate path available which satisfies the as there is no alternate path available which satisfies the
constraints, controller chooses a path that is less optimal and constraints, controller chooses a path that is less optimal and
temporarily sets up an alternate path via P1->P3->P2. Once the 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 goes for maintenance, all the links run OSPF [RFC4577]. When PE goes out of service for
links on the PE can be set to link-overlaod state which will gurantee maintenance, all the links on the PE can be set to link-overlaod
that the traffic from CEs also gets diverted. The interaction state which will gurantee that the traffic to/from dual-homed CEs
between OSPF and BGP is outside the scope of this document. gets diverted. The interaction between OSPF and BGP is outside the
scope of this document.
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 for maintenance, all sham-links on customers [RFC4577].When PE goes out of service for maintenance, all
the PE can be set to link-overload state and traffic can be divered sham-links on the PE can be set to link-overload state and traffic
from both ends without having to touch the configurations on the can be divered from both ends without having to touch 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 number OSPF is largely deployed in Hub and Spoke deployments with a number
of spokes connecting to the Hub. It is a general practice to deploy of spokes connecting to the Hub. It is a general practice to deploy
multiple Hubs with all spokes connecting to these Hubs to achieve multiple Hubs with all spokes connecting to these Hubs to achieve
redundancy. When a Hub node goes down for maintenance, all links on redundancy. When a Hub node goes down for maintenance, all links on
the Hub can be set to link-overload state and traffic gets divered the Hub can be set to link-overload state and traffic gets divered
from spoke sites as well without having to make configuration changes from the spoke sites as well without having to make configuration
on the spokes. 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:
OSPF Extended Link TLVs Registry OSPF Extended Link TLVs Registry
i) TBD - Link-Overload sub-TLV i) Link-Overload sub-TLV - Suggested value 5
OSPFV3 Router Link TLV Registry ii) Remote IPv4 address sub-TLV - Suggested value 4
i) TBD - Link-Overload sub-TLV iii) Local/Remote Interface ID sub-TLV - Suggested Value 11
OSPF RI TLV Registry OSPFV3 Router Link TLV Registry
i) TBD - Link-Overload sub-TLV i) Link-Overload sub-TLV - suggested value 4
BGP-LS Link NLRI Registry [RFC7752] BGP-LS Link NLRI Registry [RFC7752]
i)TBD - Link-Overload sub-TLV i)Link-Overload 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 link-overload is useful.
11. References 11. References
11.1. Normative References 11.1. Normative References
[RFC6845] Sheth, N., Wang, L., and J. Zhang, "OSPF Hybrid Broadcast [RFC6845] Sheth, N., Wang, L., and J. Zhang, "OSPF Hybrid Broadcast
and Point-to-Multipoint Interface Type", RFC 6845, and Point-to-Multipoint Interface Type", RFC 6845,
DOI 10.17487/RFC6845, January 2013, DOI 10.17487/RFC6845, January 2013,
skipping to change at page 13, line 14 skipping to change at page 13, line 19
[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
RFC 4915, DOI 10.17487/RFC4915, June 2007, RFC 4915, DOI 10.17487/RFC4915, June 2007,
<http://www.rfc-editor.org/info/rfc4915>. <http://www.rfc-editor.org/info/rfc4915>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<http://www.rfc-editor.org/info/rfc5340>. <http://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, <http://www.rfc-editor.org/info/rfc5817>.
[RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D. [RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 6987, McPherson, "OSPF Stub Router Advertisement", RFC 6987,
DOI 10.17487/RFC6987, September 2013, DOI 10.17487/RFC6987, September 2013,
<http://www.rfc-editor.org/info/rfc6987>. <http://www.rfc-editor.org/info/rfc6987>.
Authors' Addresses Authors' Addresses
Shraddha Hegde Shraddha Hegde
Juniper Networks, Inc. Juniper Networks, Inc.
Embassy Business Park Embassy Business Park
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