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Versions: (draft-hegde-ospf-link-overload) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 RFC 8379

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.

Copyright Notice

   Copyright (c) 2015 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
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   described in the Simplified BSD License.

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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