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INTERNET-DRAFT                                     Vijayalaxmi Basavaraj
Intended Status: Informational                               Ankur Dubey
Updates: 3623, 5187                                         Sami Boutros
                                                                  VMware

                                                             Acee Lindem
                                                                   Cisco
Expires: January 8, 2020                                    July 7, 2019


                   OSPF Graceful Restart Enhancements
         draft-basavaraj-ospf-graceful-restart-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 to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

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Copyright and License Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors. All rights reserved.




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   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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   described in the Simplified BSD License.



Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . . .  3
   2  Graceful Restart Enhancements . . . . . . . . . . . . . . . . .  3
     2.1 Stub Link Network Scenarios  . . . . . . . . . . . . . . . .  3
     2.2 Multiple Failure Scenarios . . . . . . . . . . . . . . . . .  4
   3  Security Considerations . . . . . . . . . . . . . . . . . . . .  4
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  4
   5.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     5.1  Normative References  . . . . . . . . . . . . . . . . . . .  4
     5.2  Informative References  . . . . . . . . . . . . . . . . . .  4
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .  5


























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1  Introduction

   This document describes the enhancements to the current Graceful
   restart OSPF procedure 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.


1.1  Terminology

   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].


2  Graceful Restart Enhancements

   In this section we will describe couple of issues with OSPF Graceful
   Restart (GR) in some network deployment scenarios, and a proposal to
   enhance the OSPF GR procedure to achieve faster OSPF routing
   convergence in those scenarios.

2.1 Stub Link Network Scenarios


   ---------             ---------            ---------
   |Router1|---Area 0----|Router2|---Area 1---|Router3|
   ---------             ---------            ---------

           Figure1: OSPF topology with Graceful restart


   As described in figure 1, Router2 is an area border router (ABR) with
   OSPF links in 2 areas. Furthermore. Router2 has formed full
   adjacencies only in Area 0. In Area 1, Router2 has an OSPF link
   enabled but Router2 couldn't form any adjacency either because
   Router3 is down or Router3 does not have OSPF enabled. Hence, Router2
   will only have a stub link in Area 1.

   On restart, the ABR router Router2, 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, Router2 will have to wait for the grace
   period expiry leading to slower OSPF routing convergence.

   For this we propose, if no OSPF control packets were received within



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   the dead interval on a link in Area 1 as per the above network
   scenario, Router2 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.

2.2 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 Advertisements
   (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.

3  Security Considerations

   This document does not introduce any additional security constraints.


4.  IANA Considerations

   None


5.  References

5.1  Normative References

   [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
   Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3623] Moy, J., Pillay-Esnault, P., and A. Lindem, "Graceful OSPF
   Restart", RFC 3623, November 2003.

   [RFC5187] Pillay-Esnault, P., and A. Lindem, "OSPFv3 Graceful
   Restart", RFC 5187, June 2008.


5.2  Informative References

   [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.





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Authors' Addresses



      Sami Boutros
      VMware
      Email: boutross@vmware.com

      Ankur Dubey
      VMware
      Email: adubey@vmware.com

      Vijayalaxmi Basavaraj
      VMware
      Email: vbasavaraj@vmware.com

      Acee Lindem
      Cisco
      Email: acee@cisco.com
































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