Open Shortest Path First IGP S. Hegde
Internet-Draft Juniper Networks, Inc.
Intended status: Standards Track P. Sarkar
Expires: January 8, 2017 H. Gredler
Individual
M. Nanduri
Microsoft Corporation
L. Jalil
Verizon
July 7, 2016
OSPF Link Overload
draft-ietf-ospf-link-overload-02
Abstract
When a link is being prepared to be taken out of service, the traffic
needs to be diverted from both ends of the link. Increasing the
metric to the highest metric on one side of the link is not
sufficient to divert the traffic flowing in the other direction.
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 on the link. 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/.
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 8, 2017.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Link overload sub-TLV . . . . . . . . . . . . . . . . . . . . 4
3.1. OSPF Link overload sub-TLV . . . . . . . . . . . . . . . 4
4. Flooding Scope . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Area scope flooding . . . . . . . . . . . . . . . . . . . 4
4.2. Link scope flooding . . . . . . . . . . . . . . . . . . . 5
5. Elements of procedure . . . . . . . . . . . . . . . . . . . . 5
5.1. Point-to-point links . . . . . . . . . . . . . . . . . . 5
5.2. Broadcast/NBMA links . . . . . . . . . . . . . . . . . . 6
5.3. Point-to-multipoint links . . . . . . . . . . . . . . . . 6
5.4. Unnumbered interfaces . . . . . . . . . . . . . . . . . . 6
6. Backward compatibility . . . . . . . . . . . . . . . . . . . 7
7. Applications . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Pseudowire Services . . . . . . . . . . . . . . . . . . . 7
7.2. Controller based Traffic Engineering Deployments . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
11.1. Normative References . . . . . . . . . . . . . . . . . . 9
11.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
When a node is being prepared for a planned maintenance or upgrade,
[RFC6987] 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.
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 re-routing policies at the ingress to route the LSPs away from
the link.
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 [RFC6987]
cannot be used. Application specific to this use case is described
in Section 7.1
This document provides mechanisms to advertise link overload state in
the flexible encodings provided by RI LSA( [RFC7770]) for OSPFv2 and
OSPFv3. Throughout this document, OSPF is used when the text applies
to both OSPFv2 and OSPFv3. OSPFv2 or OSPFv3 is used when the text is
specific to one version of the OSPF protocol.
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. OSPF Link overload sub-TLV
The Link Overload sub-TLV is defined as below. This sub-TLV is
attached to the Link TLV [RFC3630] and carried in RI LSA [RFC7770]
for OSPFv2 and OSPFv3
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 1: Link Overload sub-TLV for OSPFv2
Type : TBA (suggested value 35)
Length: 0
4. Flooding Scope
The link overload information can be flood in area scoped RI LSA or
link scoped RI LSA or both based on the need of the application.
Section 7 describes applications requiring area scope as well as link
scope Link-overload information. The Link TLV and the link-overload
sub-tlv MAY appear in any instance of the RI-LSA.
4.1. Area scope flooding
For OSPFv2, Link overload Sub-TLV is carried in the Link TLV as
defined in [RFC3630]. Link TLV is carried in area scoped RI LSA
[RFC7770]. When there are more than one parallel links between two
nodes, the link carrying link-overload information, need to be
uniquely identified among the parallel links. Remote interface IP
address sub-tlv as defined by [RFC3630] is also carried in the Link
TLV which is used by the remote nodes to uniquely identify the
overloaded link.
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For OSPFv3, Link-overload sub-tlv is carried in Link TLV as defined
in [RFC5329] Link TLV is carried in the OSPFv3 area scoped RI-LSA
[RFC7770]
4.2. Link scope flooding
The link local scope RI-LSA corresponds to the link on which the LSA
arrives and there is no need to explicitly carry the link TLV. The
Link overload sub-TLV is carried in the RI-LSA for both OSPFv2 and
OSPFv3.
5. Elements of procedure
The Link Overload sub-TLV indicates that the link identified in which
it is carried is overloaded. The node that has the link to be taken
out of service SHOULD originate the Link Overload sub-TLV in the Link
TLV in the RI LSA as defined in [RFC7770]. The link-overload
information is carried as a property of the link and is flooded
across the area. This information can be used by ingress routers or
controllers to take special actions. 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
link identified as overloaded depends on the link type.
5.1. Point-to-point links
The node that has the link to be taken out of service SHOULD set
metric 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 node SHOULD re-originate the TE Link Opaque
LSAs. When a Link Overload sub-TLV is received for a point-to-point
link either by link local or area scoped RI-LSA, 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.
In multi-topology deployments [RFC4915], the Link overload Sub-TLV
carried in an RI LSA corresponds to all the topologies the link
belongs to. The receiver node SHOULD change the metric in the
reverse direction corresponding to all the topologies to which the
reverse link belongs.
When the originator of the Link Overload sub-TLV purges the RI-LSA or
re-originates it without the Link Overload sub-TLV, the remote node
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must re-originate the appropriate LSAs with the metric and TE metric
values set to their original values.
5.2. 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
or advertise adjacencies with each other. For the Broadcast links,
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
would impact paths going via all neighbours.
The node that has the link to be taken out of service SHOULD set
metric 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 node SHOULD re-originate the TE Link Opaque
LSAs. 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 metric in the Network-to-Router
Metric sub-TLV to MAX-METRIC 0xffff for OSPFv2 and OSPFv3 and re-
originate the LSAs the TLV is carried-in.
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.
5.3. 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 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.
5.4. Unnumbered interfaces
Unnumbered interface do not have a unique IP addresses and borrow
address from other interfaces. The Link TLV carries the local and
remote interface ids to uniquely identify the link when there are
more than one parallel links between the nodes. Procedures to obtain
interface-id of the remote side is defined in [RFC4203] and are
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applicable to the Link TLV added in the RI LSA for the purpose of
carrying the Link overload sub-tlv.
6. 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. .
7. Applications
7.1. Pseudowire Services
---------PE3----------------PE4----------
| |
| |
CE1---------PE1----------------PE2---------CE2
| |
| |
-----------------------------------------
Private VLAN
Figure 2: 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.
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7.2. Controller based Traffic Engineering Deployments
_____________
| |
-------------| Controller |--------------
| |____________ | |
| |
|--------- Primary Path ------------------|
PE1---------P1----------------P2---------PE2
| |
| |
|________P3________|
Alternate Path
Figure 3: 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
which use 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, PE1->PE2 LSP is set-up which satisfies a
constraint of 10 GB bandwidth on each link.The links P1->P3 and
P3->P2 have only 1 GB capacity. and there is no alternate path
satisfying the bandwidth constraint of 10GB. When P1->P2 link is
being prepared for maintenance, the controller receives the link-
overload information, as there is no alternate path available which
satisfies the constraints, controller chooses a path that is less
optimal and sets up an alternate path via P1->P3->P2 temporarily.
Once the traffic is diverted, P1->P2 link can be taken out for
maintenance/upgrade.
8. Security Considerations
This document does not introduce any further security issues other
than those discussed in [RFC2328] and [RFC5340].
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9. IANA Considerations
This specification updates one OSPF registry:
OSPF Link TLVs Registry
i) TBD - Link Overload sub TLV
OSPFV3 Link TLV Registry
i) TBD - Link Overload sub TLV
OSPF Router Information (RI)TLVs Registry
i) TBD - Link TLV
10. Acknowledgements
Thanks to Chris Bowers for valuable inputs and edits to the document.
Thanks to Jeffrey Zhang and Acee Lindem for inputs.
11. References
11.1. Normative References
[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.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
DOI 10.17487/RFC3630, September 2003,
<http://www.rfc-editor.org/info/rfc3630>.
[RFC5329] Ishiguro, K., Manral, V., Davey, A., and A. Lindem, Ed.,
"Traffic Engineering Extensions to OSPF Version 3",
RFC 5329, DOI 10.17487/RFC5329, September 2008,
<http://www.rfc-editor.org/info/rfc5329>.
[RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
S. Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
February 2016, <http://www.rfc-editor.org/info/rfc7770>.
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11.2. 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>.
[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>.
[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
RFC 4915, DOI 10.17487/RFC4915, June 2007,
<http://www.rfc-editor.org/info/rfc4915>.
[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>.
[RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 6987,
DOI 10.17487/RFC6987, September 2013,
<http://www.rfc-editor.org/info/rfc6987>.
Authors' Addresses
Shraddha Hegde
Juniper Networks, Inc.
Embassy Business Park
Bangalore, KA 560093
India
Email: shraddha@juniper.net
Pushpasis Sarkar
Individual
Email: pushpasis.ietf@gmail.com
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Hannes Gredler
Individual
Email: hannes@gredler.at
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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