Internet DRAFT - draft-raunak-pim-gir-support

draft-raunak-pim-gir-support







Network Working Group                                R. Chokkanathapuram
Internet-Draft                                                R. Banthia
Intended status: Standards Track                     Cisco Systems, Inc.
Expires: December 30, 2018                                 June 28, 2018


               PIM Router Graceful Insertion and Removal
                    draft-raunak-pim-gir-support-00

Abstract

   Graceful Insertion and Removal (GIR) of routers is often adopted by
   many network administrators as an alternative to ISSU.  This document
   discusses various scenarios, requirements and possible solutions to
   make PIM gracefully shut down and isolate the multicast router with
   minimal network disruption when a router goes through maintenance
   procedures.

Status of This Memo

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   This Internet-Draft will expire on December 30, 2018.

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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.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Applicability . . . . . . . . . . . . . . . . . . . . . . . .   2
   4.  Graceful RPF change . . . . . . . . . . . . . . . . . . . . .   2
   5.  GIR removal procedure for a PIM router  . . . . . . . . . . .   3
   6.  GIR insertion procedure for a PIM router  . . . . . . . . . .   4
   7.  Compatibility . . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  PIM GIR TLV . . . . . . . . . . . . . . . . . . . . . . . . .   5
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   10. Security Considerations . . . . . . . . . . . . . . . . . . .   5
   11. Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   When a network administrator wishes to perform maintenance activity
   on a router, a system maintenance mode command need to be configured.
   This isolates the router from the network by gracefully shutting down
   various protocols running on the router.  Multicast protocols will
   also require graceful migration in order to achieve minimal traffic
   disruption when a maintenance activity is performed on a router.
   This document proposes a possible solution to perform GIR with PIM
   routers gracefully.

2.  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 [RFC2119]  .

   With respect to PIM, this document follows the terminology that has
   been defined in [RFC7761]

3.  Applicability

   The proposed change described in this specification applies to PIM
   routers only.

4.  Graceful RPF change

   Multicast routing protocol uses Unicast reachability information to
   find unique Reverse Path Forwarding Neighbor (RPF).  Any change in
   unicast routing triggers multicast RPF changes.  Multicast flows need



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   to change the RPF in a graceful manner to have minimal or no
   disruption in traffic flow.  To achieve graceful RPF change, PIM
   should not change RPF immediately following unicast routing change.
   PIM should join the new path and wait for the traffic to arrive on
   the new path before pruning the old path.  Until the packets arrive
   on the new path, the packets are accepted and forwarded on the old
   path.  Since we have not changed the RPF to new one, we would see RPF
   failures.  The RPF failures on the new path will indicate that the
   flow is available on the new path, upon which the RPF for the flows
   will be changed from old to new.  Using this method, we will be able
   to achieve non-stop forwarding of multicast traffic thereby
   minimizing traffic disruption.  The graceful RPF change, however, is
   not advisable in a normal RPF change scenario.  This is because old
   path could be down due to link failures and the RPF change may take
   more time which could increase convergence time.  Multicast flows can
   do a graceful RPF change in a GIR scenario since the flow will be
   available via the old path.

5.  GIR removal procedure for a PIM router

   A multicast router undergoing a graceful insertion/removal must
   indicate the same to all the routers in PIM domain.  This will ensure
   that all routers will gracefully change RPF for the multicast flows
   within the GIR window.  This information needs to be propagated
   before the unicast metrics are altered by the GIR router.  To achieve
   this, a PIM Flooding Mechanism message (PFM) [RFC8364] TLV is
   originated from the router undergoing GIR.  The GIR details will be
   carried in the PFM TLV.  This message is flooded periodically in the
   PIM domain and the RECOMMENDED interval to send this message is 60
   secs.  The propagation of this message will ensure that all the
   routers (in the PIM domain) knows the router undergoing GIR and can
   gracefully migrate flows from old path to new path when the unicast
   infinite metrics are advertised from the router undergoing GIR in the
   GIR window.

   Procedure for PIM routers (GIR mode)-

   1.  The router undergoing GIR (GIR router) will send a PFM message
       with a new TLV option (GIR TLV) to all its PIM neighbors
       indicating that the router wishes to go to maintenance mode.  The
       router could send more than one PFM message so that the loss of
       the PFM messages are minimized.  The value fields in the TLV will
       be populated with the following hold-time values -

       1.  graceful-rpf-start - This value indicates the seconds until
           the PIM router will start doing graceful RPF change





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       2.  graceful-rpf-stop - This value indicates the seconds after
           which the PIM router will stop doing graceful RPF change.
           The time period between the graceful-rpf-start and graceful-
           rpf-stop indicates the duration during which the routers in
           the network will do graceful RPF changes for multicast flow.

   2.  Upon receipt of the PFM message with GIR TLV option from GIR
       router, PIM neighbors will compute the RPF towards the originator
       ip address in the incoming PFM message.  If the RPF matches with
       the interface where this message is received, the router will
       perform the following, else pim will just drop the message.

       1.  Start a timer for graceful-rpf-start, if not already started.
           Once the graceful-rpf-start timer expires, the routers will
           be in graceful RPF change mode until the hold-time period
           stop.  During this time period, router will do Graceful RPF
           change (as described in section above) as soon as it receives
           unicast metric change.  The unicast infinite metric change
           from the router undergoing GIR has to be sequenced between
           the advertised graceful-rpf-start and graceful-rpf-stop.

       2.  Forward PFM message with the GIR TLV to its immediate PIM
           neighbors.  This is to propagate PFM message with the GIR TLV
           to all the routers in the PIM domain.

   The above method could be further optimized if PFM messages could
   carry the source prefixes of the multicast states present on the GIR
   router.  The routers receiving the PFM GIR message can examine the
   source prefixes and move to Graceful RPF change mode only if the
   routers have the multicast state for the source prefixes.  With this,
   not all routers needs to do Graceful RPF change.  This will ensure
   Graceful RPF change occurs only on the routers that are impacted by
   the router undergoing GIR.

6.  GIR insertion procedure for a PIM router

   The same method as described above will be used to gracefully insert
   a router with no traffic disruption after system maintenance mode.
   When a router is inserted into network, it will send the PFM GIR
   message with the graceful-rpf-start timer value set to 0, and
   graceful-rpf-stop timer set to seconds until Graceful RPF stop.
   During this window, the inserted router will start bringing up the
   unicast protocols.  Every router in the PIM domain will examine the
   PFM message and do a Graceful RPF change for the window specified in
   the message.  Once the GIR router is inserted and fully operational,
   it should send at least one message with both timers (graceful-rpf-
   start and graceful-rpf-stop) set to 0




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7.  Compatibility

   The router undergoing GIR must set the Transitive bit to 1 in the PFM
   message so that when a router that doesn't support GIR, receives a
   PFM GIR TLV, it will forward the message to the PIM neighbors.

8.  PIM GIR TLV

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |1|        Type = TBD             |         Length = 8          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       Graceful RPF Start                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       Graceful RPF Stop                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     Figure 1: PIM GIR TLV


   where

      Type : TBD

      Length : The length of the value in octets

      Graceful RPF Start : Timer value in seconds until PIM router start
      doing graceful RPF change

      Graceful RPF Stop : Timer value in seconds after which the PIM
      router will stop doing graceful RPF change

9.  IANA Considerations

   A new PIM PFM option is TBD for GIR.

10.  Security Considerations

   Security of the new PFM TLV is only guaranteed by the security of PFM
   message, so the security considerations for PFM message as described
   in [RFC8364] apply here.

11.  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>.



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   [RFC7761]  Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
              Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
              Multicast - Sparse Mode (PIM-SM): Protocol Specification
              (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
              2016, <https://www.rfc-editor.org/info/rfc7761>.

   [RFC8364]  Wijnands, IJ., Venaas, S., Brig, M., and A. Jonasson, "PIM
              Flooding Mechanism (PFM) and Source Discovery (SD)",
              RFC 8364, DOI 10.17487/RFC8364, March 2018,
              <https://www.rfc-editor.org/info/rfc8364>.

Authors' Addresses

   Ramakrishnan Chokkanathapuram
   Cisco Systems, Inc.
   Tasman Drive
   San Jose  CA  95134
   United States of America

   Email: ramaksun@cisco.com


   Raunak Banthia
   Cisco Systems, Inc.
   Tasman Drives
   San Jose  CA  95134
   United States of America

   Email: rbanthia@cisco.com






















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