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LSR Working Group                                             S. Boutros
Internet-Draft                                                  A. Dubey
Intended status: Standards Track                            V. Basavaraj
Expires: December 31, 2020                                        VMware
                                                               A. Lindem
                                                           Cisco Systems
                                                           June 29, 2020


                   OSPF Graceful Restart Enhancements
              draft-basavaraj-lsr-ospf-gr-enhancements-01

Abstract

   This document describes enhancements to the OSPF graceful restart
   procedures to improve routing convergence in some OSPF network
   deployments.  This document updates RFC 3623 and RFC 5187.

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
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   This Internet-Draft will expire on December 31, 2020.

Copyright Notice

   Copyright (c) 2020 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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   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of




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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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   2
   3.  Graceful Restart Enhancements . . . . . . . . . . . . . . . .   2
     3.1.  Stub-Link Network Scenarios . . . . . . . . . . . . . . .   2
     3.2.  Multiple Failure Scenarios  . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   3
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   This document describes the enhancements to the current OSPF
   [RFC2328] and OSPFv3 [RFC5340] graceful restart procedures as
   respectively defined in OSPF Graceful Restart [RFC3623] and OSPFv3
   Graceful Restart [RFC5187] to improve routing convergence in certain
   OSPF network deployment scenarios.  The goal is for both the
   restarting OSPF node and the helper OSPF node to terminate the OSPF
   graceful restart procedure faster and not wait for the grace period
   expiry in those network scenarios and hence improve the overall OSPF
   network convergence.

2.  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Graceful Restart Enhancements

3.1.  Stub-Link Network Scenarios

          +--------+             +--------+            +--------+
          |Router-1|---Area 0----|Router-2|---Area 1---|Router-3|
          +------=-+             +--------+            +--------+

                  Figure 1: OSPF topology with Graceful Restart




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   As graphically depicted in figure 1, Router-2 is an area border
   router (ABR) with OSPF links in 2 areas.  Furthermore, Router-2 has
   formed full adjacencies only in Area 0.  In Area 1, Router-2 has an
   OSPF link enabled but Router2 could not form an adjacency either
   because Router-3 is down or Router-3 does not have OSPF enabled.
   Hence, Router-2 will only have a stub link in Area 1.

   On restart, the ABR router Router-2, having only a stub link in the
   Area 1, will never receive its pre-restart LSA in this area and will
   never form an adjacency and will have to wait for the grace period
   expiry leading to slower OSPF routing convergence.

   For this scenario, if no OSPF control packets are received within the
   dead interval on a link in Area 1 as per the above network scenario,
   Router-2 MUST mark the link as stub and MUST not wait for the grace
   period to form an adjacency on this link to successfully Exit GR.

3.2.  Multiple Failure Scenarios

   In scenarios where more than one router is restarting at the same
   time in the same OSPF area and StrictLSAChecking is disabled,
   restarting OSPF routers will end up waiting the entire grace interval
   to exit GR.  If the restarting routers receive a Grace Link State
   Advertisement (LSA) from another router in a given area after
   restart, and the helper routers receive grace LSAs from more than one
   router, this will indicate that there have been multiple failures.
   Therefore, the helper and restarting routers MUST terminate GR and
   avoid any unnecessary delay in OSPF routing convergence.

4.  Security Considerations

   The security considerations in OSPF Graceful Restart [RFC3623] and
   OSPFv3 Graceful Restart [RFC5187] are applicable.  This document does
   not introduce any additional security considerations.

5.  IANA Considerations

   This specification doesn not require any IANA assignments.

6.  Acknowledgements

   TBD

7.  References







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7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3623]  Moy, J., Pillay-Esnault, P., and A. Lindem, "Graceful OSPF
              Restart", RFC 3623, DOI 10.17487/RFC3623, November 2003,
              <https://www.rfc-editor.org/info/rfc3623>.

   [RFC5187]  Pillay-Esnault, P. and A. Lindem, "OSPFv3 Graceful
              Restart", RFC 5187, DOI 10.17487/RFC5187, June 2008,
              <https://www.rfc-editor.org/info/rfc5187>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

7.2.  Informative References

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <https://www.rfc-editor.org/info/rfc2328>.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <https://www.rfc-editor.org/info/rfc5340>.

Authors' Addresses

   Sami Boutros
   VMware

   Email: sboutros@vmware.com


   Ankur Dubey
   VMware

   Email: adubey@vmware.com


   Vijayalaxmi Basavaraj
   VMware

   Email: vbasavaraj@vmware.com




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   Acee Lindem
   Cisco Systems
   301 Midenhall Way
   Cary, NC  27513
   USA

   Email: acee@cisco.com












































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