Open Shortest Path First IGP S. Hegde
Internet-Draft P. Sarkar
Intended status: Standards Track H. Gredler
Expires: April 21, 2016 Juniper Networks, Inc.
M. Nanduri
Microsoft Corporation
L. Jalil
Verizon
October 19, 2015
OSPF Link Overload
draft-ietf-ospf-link-overload-00
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, the existing stub router mechanism described in [RFC3137]
cannot be used.
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
impending maintenance activity in the underlying network devices.
This information can be used by the network devices to re-route the
traffic effectively.
This document describes the protocol extensions to disseminate link
overload information in OSPFv2 and OSPFv3.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference
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This Internet-Draft will expire on April 21, 2016.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Link overload sub-TLV . . . . . . . . . . . . . . . . . . . . 4
3.1. OSPFv2 Link overload sub-TLV . . . . . . . . . . . . . . 4
3.2. OSPFv3 Link Overload sub-TLV . . . . . . . . . . . . . . 4
4. Elements of procedure . . . . . . . . . . . . . . . . . . . . 5
4.1. Point-to-point links . . . . . . . . . . . . . . . . . . 5
4.2. Broadcast/NBMA links . . . . . . . . . . . . . . . . . . 5
4.3. Point-to-multipoint links . . . . . . . . . . . . . . . . 6
4.4. Unnumbered interfaces . . . . . . . . . . . . . . . . . . 6
5. Backward compatibility . . . . . . . . . . . . . . . . . . . 6
6. Applications . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Pseudowire Services . . . . . . . . . . . . . . . . . . . 7
6.2. Controller based Traffic Engineering Deployments . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
When a node is being prepared for a planned maintenance or upgrade,
[RFC3137] provides mechanisms to advertise the node being in an
overload state by setting all outgoing link costs to MAX-METRIC
(0xffff). These procedures are specific to the maintenance activity
on a node and cannot be used when a single link attached to the node
requires maintenance.
When a link is being prepared to be taken out of service, the traffic
needs to be diverted from both ends of the link. Changing the metric
on one side of the link is not sufficient to divert the traffic
flowing in both directions. In traffic-engineering deployments, LSPs
need to be moved away from the link without disrupting the services.
It is useful to be able to advertise the impending maintenance
activity on the link and to have LSP rerouting policies at the
ingress to route the LSPs away from the link.
It is useful for routers in OSPFv2 or OSPFv3 routing domain to be
able to advertise a link being in an overload state to indicate
impending maintenance activity on the link. This document provides
mechanisms to advertise link overload state in the flexible encodings
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. Motivation
The motivation of this document is to reduce manual intervention
during maintenance activities. The following objectives help to
accomplish this in a range of deployment scenarios.
1. Advertise impending maintenance activity so that the traffic from
both directions can be diverted away from the link.
2. Allow the solution to be backward compatible so that nodes that
do not understand the new advertisement do not cause routing
loops.
3. Advertise the maintenance activity to other nodes in the network
so that LSP ingress routers/controllers can learn the impending
maintenance activity and apply specific policies to re-route the
LSP for traffic-engineering based deployments.
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4. Allow the link to be used as last resort link to prevent traffic
disruption when alternate paths are not available.
3. Link overload sub-TLV
3.1. OSPFv2 Link overload sub-TLV
The 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 the overload state when there
are multiple parallel links between two nodes.
3.2. OSPFv3 Link Overload sub-TLV
The 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.
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
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Type : TBA
Length: 0
4. Elements of procedure
The Link Overload sub-TLV indicates that the link identified in by
the sub-TLV is overloaded. The node that has the link to be taken
out of service sets metric of the link to MAX-METRIC (0xffff) and re-
originates the Router-LSA. The TE metric is set to MAX-TE-METRIC-1
(0xfffffffe) and the node also re-originates the TE Link Opaque LSAs.
The node SHOULD originate the Link Overload sub-TLV in the Extended
Link TLV in the Extended Link Opaque LSA as defined in
[I-D.ietf-ospf-prefix-link-attr] for OSPFv2 or in the E-Router-LSA as
defined in [I-D.ietf-ospf-ospfv3-lsa-extend] for OSPFv3. This LSA
should be flooded in the OSPF area. A node which supports this draft
and is at the remote end of the link identified in the Link Overload
sub-TLV MUST set the metric of the link in the reverse direction to
MAX-METRIC. In addition, the TE metric MUST be changed to
0xfffffffe. The remote node MUST re-originate the Router-LSA and TE
link opaque LSA with these updated metrics, and flood them into the
area.
When the originator of the Link Overload sub-TLV purges the Extended
Link Opaque LSA or re-originates it without the Link Overload sub-
TLV, the remote node must re-originate the appropriate LSAs with the
metric and TE metric values set to their original values.
The precise action taken by the remote node at the other end of the
link identified as overloaded depends on the link type.
4.1. Point-to-point links
When a Link Overload sub-TLV is received for a point-to-point link
the remote node SHOULD identify the local link which corresponds to
the overloaded link and set the metric to MAX-METRIC (0xffff). The
remote node MUST re-originate the router-LSA with the changed metric
and flood into the OSPF area. The TE metric SHOULD be set to MAX-TE-
METRIC-1 (0xfffffffe) and the TE opaque LSA for the link MUST be re-
originated with new value.
4.2. 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 logically. 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
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or 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.
For a broadcast link, the two part metric as described in
[I-D.ietf-ospf-two-part-metric] is used. The node originating the
Link Overload sub-TLV MUST set the MT metric in the Network-to-Router
Metric sub-TLV to MAX-METRIC 0xffff for OSPFv2 and OSPFv3. The nodes
that receive the two part metric should follow the procedures
described in [I-D.ietf-ospf-two-part-metric]. The backward
compatibility procedures described in [I-D.ietf-ospf-two-part-metric]
should be followed to ensure loop free routing.
4.3. Point-to-multipoint links
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
point-to-multipoint link the remote node SHOULD identify the neighbor
which corresponds to the overloaded link and set the metric to MAX-
METRIC (0xffff). The remote node MUST re-originate the Router-LSA
with the changed metric and flood into the OSPF area.
4.4. Unnumbered interfaces
Unnumbered interface do not have a unique IP addresses and borrow
address from other interfaces. [RFC2328] describes procedures to
handle unnumbered interfaces. The link-data field in the Extended
Link TLV carries the interface-id instead of the IP address. The
Link Overload sub-TLV carries the remote interface-id in the Remote-
ip-address field if the interface is unnumbered. Procedures to
obtain interface-id of the remote side is defined in [RFC4203].
5. Backward compatibility
The mechanism described in the document is fully backward
compatible.It is required that the originator of the Link Overload
sub-TLV as well as the node at the remote end of the link identified
as overloaded understand the extensions defined in this document. In
the case of broadcast links, the backward compatibility procedures as
described in [I-D.ietf-ospf-two-part-metric] are applicable. .
6. Applications
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6.1. Pseudowire Services
---------PE3----------------PE4----------
| |
| |
CE1---------PE1----------------PE2---------CE2
| |
| |
-----------------------------------------
Private VLAN
Figure 3: Pseudowire Services
Many service providers offer pseudo-wire services to customers using
L2 circuits. The IGP protocol that runs in the customer network
would also run over the pseudo-wire to create 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 an
alternate path. There can be large number of customers attached to a
PE node and the remote end-points for these pseudo-wires are spread
across the service provider's network. It is a tedious and error-
prone process to change the metric for all pseudo-wires in both
directions. The link overload feature simplifies the process by
increasing the metric on the link in the reverse direction as well so
that traffic in both directions is diverted away from the PE
undergoing maintenance. The link-overload feature allows the link to
be used as a last resort link so that traffic is not disrupted when
alternative paths are not available.
6.2. Controller based Traffic Engineering Deployments
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_____________
| |
-------------| Controller |--------------
| |____________ | |
| |
| ------- Primary Path --------------- |
PE1---------P1----------------P2---------PE2
| |
| |
|________P3________|
Alternate Path
Figure 4: Controller based Traffic Engineering
In controller-based deployments where the controller participates in
the IGP protocol, the controller can also receive the link-overload
information as a warning that link maintenance is imminent. Using
this information, the controller can find alternate paths for traffic
using the affected link. The controller can apply various policies
and re-route the LSPs away from the link undergoing maintenance. If
there are no alternate paths satisfying the traffic engineering
constraints, the controller might temporarily relax those constraints
and put the service on a different path. In the above example when
P1->P2 link is being prepared for maintenance, the controller
receives 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.
7. Security Considerations
This document does not introduce any further security issues other
than those discussed in [RFC2328] and [RFC5340].
8. IANA Considerations
This specification updates one OSPF registry:
OSPF Extended Link TLVs Registry
i) TBD - Link Overload sub TLV
OSPFV3 Router Link TLV Registry
i) TBD - Link Overload sub TLV
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9. Acknowledgements
Thanks to Chris Bowers for valuable inputs and edits to the document.
10. References
10.1. Normative 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.
[I-D.ietf-ospf-two-part-metric]
Wang, L., Lindem, A., DuBois, D., Julka, V., and T.
McMillan, "OSPF Two-part Metric", draft-ietf-ospf-two-
part-metric-01 (work in progress), July 2015.
10.2. Informative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<http://www.rfc-editor.org/info/rfc2328>.
[RFC3137] Retana, A., Nguyen, L., White, R., Zinin, A., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 3137,
DOI 10.17487/RFC3137, June 2001,
<http://www.rfc-editor.org/info/rfc3137>.
[RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,
<http://www.rfc-editor.org/info/rfc4203>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<http://www.rfc-editor.org/info/rfc5340>.
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Authors' Addresses
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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