Open Shortest Path First IGP S. Hegde
Internet-Draft P. Sarkar
Intended status: Standards Track H. Gredler
Expires: January 17, 2016 Juniper Networks, Inc.
M. Nanduri
Microsoft Corporation
L. Jalil
Verizon
July 16, 2015
OSPF Link Overload
draft-hegde-ospf-link-overload-01
Abstract
Many OSPFv2 or OSPFv3 deployments run on overlay networks provisioned
by means of pseudo-wires or L2-circuits. when the devices in the
underlying network go for maintenance, it is useful to divert the
traffic away from the node before the maintenance is actually
scheduled. Since the nodes in the underlying network are not visible
to OSPF, existing stub router mechanism described in [RFC3137] cannot
be used. It is useful for routers in OSPFv2 or OSPFv3 routing domain
to be able to advertise a link being in overload state to indicate
impending maintenance activity in the underlying network devices.
This document describes the protocol extensions to disseminate link
overload information in OSPFv2 and OSPFv3 protocol.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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 of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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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 January 17, 2016.
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Link overload sub TLV . . . . . . . . . . . . . . . . . . . . 3
2.1. OSPFv2 Link overload sub TLV . . . . . . . . . . . . . . 3
2.2. OSPFv3 Link overload sub TLV . . . . . . . . . . . . . . 3
3. Elements of procedure . . . . . . . . . . . . . . . . . . . . 4
3.1. Point-to-point links . . . . . . . . . . . . . . . . . . 4
3.2. Broadcast/NBMA links . . . . . . . . . . . . . . . . . . 4
3.3. Point-to-multipoint links . . . . . . . . . . . . . . . . 5
4. Backward compatibility . . . . . . . . . . . . . . . . . . . 5
5. Applications . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Pseudowire Services . . . . . . . . . . . . . . . . . . . 5
5.2. Controller based Traffic Engineering Deployments . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
It is useful for routers in OSPFv2 or OSPFv3 routing domain to be
able to advertise a link being in overload state to indicate
impending maintenance activity on the link. This document provides
mechanisms to advertise link overload state in the flexible encodings
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provided by OSPFv2 Prefix/Link Attribute Advertisement(
[I-D.ietf-ospf-prefix-link-attr]) and OSPFv3 Extended LSA
([I-D.ietf-ospf-ospfv3-lsa-extend]). 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. Link overload sub TLV
2.1. OSPFv2 Link overload sub TLV
Link overload sub TLV is carried as part of the Extended link TLV as
defined in [I-D.ietf-ospf-prefix-link-attr] for OSPFv2.
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 IP address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Link overload sub TLV for OSPFv2
Type : TBA
Length: 4
Value: Remote IPv4 address. The remote IP4 address is used to
identify the particular link that is in overload state when there are
multiple parallel links between two nodes.
2.2. OSPFv3 Link overload sub TLV
Link overload sub TLV is carried in the Router-link TLV as defined in
the [I-D.ietf-ospf-ospfv3-lsa-extend] for OSPFv3. The Router-Link
TLV contains the neighbor interface-id and can uniquely identify the
link on the remote node.
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Link overload sub TLV for OSPFv3
Type : TBA
Length: 0
3. Elements of procedure
The Link Overload sub TLV indicates that the Link which carries the
sub TLV is overloaded. The node that has the link going for
maintenance, sets metric of the link to MAX-METRIC and re-originates
the router LSA. The metric in the reverse direction also need to
change to divert the traffic from reverse direction. The node SHOULD
originate Link overload sub TLV and include it in Extended link TLV
and originate the Extended Link Opaque LSA as defined in
[I-D.ietf-ospf-prefix-link-attr] for OSPFv2 and E-Router-LSA as
defined in [I-D.ietf-ospf-ospfv3-lsa-extend] for OSPFv3 and flood in
the OSPF area.
when the originator of the Link Overload sub TLV, purges the extended
link opaque LSA or re-originates without the Link Overload sub TLV,
the metric on the remote node SHOULD be changed back to the original
value.
Based on the link type of the overloaded link below actions MAY be
taken by the receiver.
3.1. Point-to-point links
When a link overload TLV is received for a point-to-point link the
receiver SHOULD identify the local link which corresponds to the
overloaded link and set the metric to MAX-METRIC (0xffff). Receiver
node MUST re-originate the router-LSA with the changed metric and
flood into the OSPF area.
3.2. Broadcast/NBMA links
Broadcast or 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 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 do not form or
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advertise adjacencies with each other. For the Broadcast links, the
MAX-METRIC on the outgoing link cannot be changed since all the
neighbors are on same link. Setting the link cost to MAX-METRIC
would impact paths going via all neighbors.
When a link-overload TLV is received by the remote end for a
broadcast/NBMA link
- If it's DROther or BDR for that link, SHOULD not take any action.
- If receiving node is DR for the link, it MUST remove the originator
of the link overload TLV from the list of connected neighbors and
MUST re-originate the network LSA and flood into the OSPF area.
3.3. Point-to-multipoint links
Operation for the point-to-multipoint links is similar to the point-
to-point links. When a link overload TLV is received for a point-to-
multipoint link the receiver SHOULD identify the neighbor which
corresponds to the overloaded link and set the metric to MAX-METRIC
(0xffff). Receiver node MUST re-originate the router-LSA with the
changed metric and flood into the OSPF area.
4. Backward compatibility
The mechanism described in the document is fully backward
compatible.It is required that the originator and receiver of link-
overload sub TLV understand the extensions defined in this document
and in case of broadcast links the originator and the DR need to
understand the extensions. Other nodes in the network compute based
on increased metric and hence the feature is backward compatible.
5. Applications
5.1. Pseudowire Services
---------PE3----------------PE4----------
| |
| |
CE1---------PE1----------------PE2---------CE2
| |
| |
-----------------------------------------
Private VLAN
Figure 3: Pseudowire Services
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Many service providers offer pseudo-wire services to customers using
L2 circuits. The IGP protocol that runs in the customer network
would also to run over the pseudo-wire to get seamless private
network for the customer. Service providers want to offer overload
kind of functionality when the PE device is taken-out for
maintenance.The provider should guarantee that the PE is taken out
for maintenance only after the service is successfully diverted on
the alternate path. Link overload feature provides facilities to
achieve this service by increasing the metric on the link but still
allowing the traffic to use the link when there is no alternate path
available.
5.2. Controller based Traffic Engineering Deployments
_____________
| |
-------------| Controller |--------------
| |____________ | |
| |
| ------- Primary Path --------------- |
PE1---------P1----------------P2---------PE2
| |
| |
|________P3________|
Alternate Path
Figure 4: Controller based Traffic Engineering
Controller based deployments where the controller participates in the
IGP protocol gets the link-overload information when the link
maintenance is impending. Using this information controller finds an
alternate path. If there are no alternate paths satisfying the
traffic engineering constraints, controller might temporarily relax
the constraints and put the service on different path. In the above
example when P1->P2 link goes for maintenance, controller gets the
link-overload information and sets up an alternate path via
P1->P3->P2. Once the traffic is diverted, P1->P2 link can be taken
out for maintenance/upgrade.
6. Security Considerations
This document does not introduce any further security issues other
than those discussed in [RFC2328] and [RFC5340].
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7. IANA Considerations
This specification updates one OSPF registry:
OSPF Extended Link TLVs Registry
i) TBD - Link Overload TLV OSPFV3 Router Link TLV Registry
i) TBD - Link Overload TLV
8. Acknowledgements
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC3137] Retana, A., Nguyen, L., White, R., Zinin, A., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 3137,
June 2001.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.
9.2. Informative References
[I-D.ietf-ospf-ospfv3-lsa-extend]
Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3
LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-06
(work in progress), February 2015.
[I-D.ietf-ospf-prefix-link-attr]
Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", draft-ietf-ospf-prefix-link-attr-03 (work
in progress), February 2015.
Authors' Addresses
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Shraddha Hegde
Juniper Networks, Inc.
Embassy Business Park
Bangalore, KA 560093
India
Email: shraddha@juniper.net
Pushpasis Sarkar
Juniper Networks, Inc.
Embassy Business Park
Bangalore, KA 560093
India
Email: psarkar@juniper.net
Hannes Gredler
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
US
Email: hannes@juniper.net
Mohan Nanduri
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
Email: mnanduri@microsoft.com
Luay Jalil
Verizon
Email: luay.jalil@verizon.com
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