Internet DRAFT - draft-zhang-idr-transitive-gr

draft-zhang-idr-transitive-gr



 



Network Working Group                                           H. Zhang
Internet-Draft                                  HangZhou H3C Co. Limited
Updates: RFC 4724 (if approved)                                A. Retana
Intended status: Standards Track                     Cisco Systems, Inc.
Expires: September 26, 2013                               March 25, 2013


                    Transitive BGP Graceful Restart
                    draft-zhang-idr-transitive-gr-02

Abstract

   This document defines an extension to BGP Graceful Restart that
   reduces the negative impact of multiple inter-connected routers
   restarting.  The proposed mechanism does not require any changes to
   the BGP protocol.

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
   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 May 18, 2013.

Copyright Notice

   Copyright (c) 2013 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
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.
 


Zhang & Retana         Expires September 26, 2013               [Page 1]

Internet-Draft             Transitive BGP GR              March 25, 2013


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . . . 3
   3.  Proposed Solution . . . . . . . . . . . . . . . . . . . . . . . 4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
     7.2.  Informative References  . . . . . . . . . . . . . . . . . . 5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 5




































 


Zhang & Retana         Expires September 26, 2013               [Page 2]

Internet-Draft             Transitive BGP GR              March 25, 2013


1.  Introduction

   The BGP Graceful Restart [RFC4724] process defines a mechanism that a
   restarting router can use with its non-restarting peers.  The
   existence of other restarting routers results in the use of the base
   route exchange mechanism [RFC4271] with them, even if the forwarding
   state has indeed been preserved for (and by) those peers during the
   restart.  As a result, traffic forwarding between restarting routers
   is disrupted.

   This document defines an extension to BGP Graceful Restart that
   reduces the negative impact of multiple inter-connected restarting
   routers.  The proposed mechanism does not require any changes to the
   BGP protocol.

   The current process [RFC4724] states that routes from restarting
   peers are to be removed from the local forwarding state when the non-
   restarting peers converge (the End-of-RIB marker is received from all
   of them).  Assuming a simple topology:

      NR1 - R2 - R3 - NR2

      where NRx are non-restarting routers, Rx are restarting routers
      and the lines between them represent BGP sessions.

   There are two types of routes affected (from R2's point of view) by
   the current process:

   1.  Routes that are only reachable through R3.  These routes will be
       removed from the forwarding table when the non-restarting routers
       converge, and installed back in when the convergence with R3 is
       done.

   2.  Routes that are reachable through both R3 and NR1.  These routes
       will first change to NR1 when the non-restarting routers
       converge, and later back to R3 (assuming that is in fact still
       the preferred path).

   Both types can clearly cause disruption in traffic forwarding, micro-
   loops, traffic loss, etc.


2.  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 [RFC2119].

 


Zhang & Retana         Expires September 26, 2013               [Page 3]

Internet-Draft             Transitive BGP GR              March 25, 2013


3.  Proposed Solution

   The extension proposed to BGP Graceful Restart to accommodate for
   multiple restarting routers, when the forwarding state has been
   preserved between them, is simply to delay sending the End-of-RIB
   marker to non-restarting routers.

   Specifically, to allow a restarting router the ability to reduce the
   impact due to other restarting routers, the following paragraph is
   added as the fifth one in section 4.1 (Procedures for the Restarting
   Speaker) [RFC4724]:

      Before updating the corresponding forwarding states, the
      Restarting Speaker MAY start a path calculation after all non-
      retarting peers's End-Of-RIB marker have been received, and
      advertise the Adj-RIB-Out to its restarting peers (ones with the
      "Restart State" bit set in the received capability), including the
      End-of-RIB marker, and wait for the corresponding End-of-RIB
      marker from them.

   In order to maintain the transitive property when more than two BGP
   speakers peering with each other restart, the following paragraph is
   added as the sixth one in section 4.1 (Procedures for the Restarting
   Speaker) [RFC4724]:

      If the Restarting Speaker has multiple restarting peers, sending
      the End-of-RIB marker SHOULD be delayed until all the markers from
      those restarting peers have been received.  The BGP speaker on a
      given connection SHOULD send its End-of-RIB marker if the pair
      hasn't sent or received UPDATES for a locally configured time
      period (which SHOULD be significantly less than the
      Selection_Deferral_Timer).

   During the recovery period of multiple restarting routers, a BGP
   speaker may advertise routing information that is not being used at
   the time.  Because the forwarding state of the speakers remains
   unchanged (from that at the restart), it is clear that this
   transitive property of sharing routing information between restarting
   routers doesn't cause any issues in the actual forwarding of traffic.
   Furthermore, it has the advantage if avoiding further disruptions in
   the forwarding of traffic through the restarting routers.


4.  Security Considerations

   This document proposes an extension to an existing mechanism.  The
   same security considerations explained there apply to this extension.

 


Zhang & Retana         Expires September 26, 2013               [Page 4]

Internet-Draft             Transitive BGP GR              March 25, 2013


   The propagation of routing information that is not in use may cause
   forwarding loops and an inconsistent state in a network.  However,
   the risk in this document is mitigated by the fact that the
   information is validated by all peers once the convergence process
   completes.


5.  IANA Considerations

   This document has no IANA actions.


6.  Acknowledgements

   The authors would like to thank Enke Chen, John Scudder, Robert
   Raszuk and Abhay Roy for their feedback.


7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4724]  Sangli, S., Chen, E., Fernando, R., Scudder, J., and Y.
              Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724,
              January 2007.

7.2.  Informative References

   [RFC4271]  Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
              Protocol 4 (BGP-4)", RFC 4271, January 2006.


Authors' Addresses

   Haifeng Zhang
   HangZhou H3C Co. Limited
   310 Liuhe Road, Zhijiang Science Park
   Hangzhou
   P.R. China

   Email: zhanghf@h3c.com




 


Zhang & Retana         Expires September 26, 2013               [Page 5]

Internet-Draft             Transitive BGP GR              March 25, 2013


   Alvaro Retana
   Cisco Systems, Inc.
   7025 Kit Creek Rd.
   Research Triangle Park, NC  27709
   USA

   Email: aretana@cisco.com












































Zhang & Retana         Expires September 26, 2013               [Page 6]