VRRP PIM Interoperability
draft-zhou-pim-vrrp-04

Network Working Group                                            W. Zhou
Internet-Draft                                             cisco Systems
Intended status: Informational                          January 21, 2016
Expires: July 24, 2016

                       VRRP PIM Interoperability
                       draft-zhou-pim-vrrp-04.txt

Abstract

   This document introduces VRRP Aware PIM, a redundancy mechanism for
   the Protocol Independent Multicast (PIM) to interoperate with Virtual
   Router Redundancy Protocol (VRRP).  It allows PIM to track VRRP state
   and to preserve multicast traffic upon failover in a redundant
   network with virtual routing groups enabled.

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   This Internet-Draft will expire on July 24, 2016.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Tracking and Failover . . . . . . . . . . . . . . . . . . . .   3
   3.  PIM Assert Metric Auto-Adjustment . . . . . . . . . . . . . .   3
   4.  DF Election for BiDir Group . . . . . . . . . . . . . . . . .   4
   5.  Tracking Multiple VRRP Groups on an Interface . . . . . . . .   4
   6.  Support of HSRP . . . . . . . . . . . . . . . . . . . . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   10. Informative References  . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Virtual Router Redundancy Protocol (VRRP) [RFC5798] is a redundancy
   protocol for establishing a fault-tolerant default router.  The
   protocol establishes a framework between network devices in order to
   achieve default router failover if the primary router becomes
   inaccessible.

   PIM [RFC4601] has no inherent redundancy capabilities and its
   operation is completely independent of VRRP group states.  As a
   result, IP multicast traffic is forwarded not necessarily by the same
   device as is elected by VRRP.  The VRRP Aware PIM feature provides
   consistent IP multicast forwarding in a redundant network with
   virtual routing groups enabled.

   In a multi-access segment (such as LAN), PIM designated router (DR)
   election is unaware of the redundancy configuration, and the elected
   DR and VRRP master router (MR) may not be the same router.  In order
   to ensure that the PIM DR is always able to forward PIM Join/Prune
   (J/P) message towards RP or FHR, the VRRP MR becomes the PIM DR (if
   there is only one VRRP group).  PIM is responsible for adjusting DR
   priority based on the group state.  When a failover occurs, multicast
   states are created on the new MR elected by the VRRP group and the MR
   assumes responsibility for the routing and forwarding of all the
   traffic addressed to the VRRP virtual IP address.  This ensures the
   PIM DR runs on the same gateway as the VRRP MR and maintains mroute
   states.  It enables multicast traffic to be forwarded through the
   VRRP MR, allowing PIM to leverage VRRP redundancy, avoid potential
   duplicate traffic, and enable failover, depending on the VRRP states
   in the device.

   All routers forming a VRRP group need to support this mechanism in
   order to achieve correct behavior.  Other routers that do not support
   the mechanism on the link will not break the functionality of this

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   mechanism, as long as their DR priority configurations do not
   conflict with the routers in the VRRP group.

2.  Tracking and Failover

   Without the mechanisms described in this document, PIM daemon will
   send PIM J/P with DR's IP address to upstream routers.  A GenId in
   PIM Hello message is randomly selected when the router boots and
   remains the same as long as the router is up.  A PIM neighbor reboot
   can easily be detected if its GenId is different from before, in this
   case PIM J/P and RP-Set information can be redistributed to the new
   rebooted neighbor.  With VRRP aware PIM mechasim enabled, PIM damon
   listens to the state change notifications from VRRP and automatically
   adjusts the priority of the PIM DR based on the VRRP state, and
   ensures VRRP MR (if there is only one VRRP group) becomes the DR of
   the LAN.  If there are multiple VRRP groups, the DR is determined by
   user-configured priority.

   Upon failover, PIM daemon triggers communication between upstream and
   downstream devices in order to create mroute states on the new MR.
   PIM daemon sends additional PIM Hello message using the VRRP virtual
   IP addresses as the source address for each active VRRP group when a
   device becomes VRRP Master.  The PIM Hello message with new GenID
   will trigger other routers to respond to the VRRP failover just the
   same way as to neighbor reboot.  When a downstream device receives
   this PIM Hello, it will add the virtual address to its PIM neighbor
   list, and immediately send triggered PIM J/P messages towards the
   virtual IP address.  Upstream routers will process PIM J/P based on
   VRRP group state.  If the PIM J/P destination address matches the
   VRRP group virtual address and if the destination device is in VRRP
   master state, the current VRRP MR processes the PIM J/P message.
   This allows all PIM J/P to reach the VRRP group virtual address and
   minimizes changes and configurations at the downstream routers side.

   Alternatively, implementation can choose to have all passive routers
   maintain mroute states and record the GenID of current MR.  When a
   passive router becomes MR upon failover, it uses the existing mroute
   states and the recorded MR GenID in its Hello message.  This will
   avoid resending PIM J/P messages upon failover and eliminates the
   requirement of additional PIM Hello with virtual IP address.  There
   is no change in on-wire behavior or in the PIM/VRRP message format.

3.  PIM Assert Metric Auto-Adjustment

   It is possible that, after VRRP master switched from A to B; A is
   still forwarding multicast traffic which will result in duplicate
   traffic and PIM Assert mechanism will kick in.  PIM Assert with
   redundancy is enabled.

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   o  If only one VRRP group, passive routers will send a large penalty
      metric preference (PIM_ASSERT_INFINITY - 1) and make MR the Assert
      winner.

   o  If there are multiples VRRP groups configured on an interface,
      Assert metric preference will be (PIM_ASSERT_INFINITY - 1) if and
      only if all VRRP groups are in passive state.

   o  If there is at least one VRRP group is in Active, then original
      Assert metric preference will be used.  That is, winner will be
      selected between routers using their real Assert metric preference
      with at least one active VRRP Group, just like no VRRP is
      involved.

4.  DF Election for BiDir Group

   Change to DF offer/winner metric is handled similarly to PIM Assert
   handling with VRRP.

   o  If only one VRRP group, passive routers will send a large penalty
      metric preference in Offer (PIM_BIDIR_INFINITY_PREF- 1) and make
      MR the DF winner.

   o  If there are multiples VRRP groups configured on an interface,
      Offer metric preference will be (PIM_BIDIR_INFINITY_PREF- 1) if
      and only if all VRRP groups are in passive.

   o  If there is at least one VRRP group is in Active, then original
      Offer metric preference to RP will be used.  That is, winner will
      be selected between routers using their real Offer metric with at
      least one active VRRP Group, just like no VRRP is involved.

5.  Tracking Multiple VRRP Groups on an Interface

   User can configure PIM to track more than one VRRP groups on an
   interface.  This allows other applications to exploit the PIM/VRRP
   interoperability to achieve various goals (e.g., load balancing).
   Since each VRRP groups configured on an interface could be in
   different states at any moment, the DR priority is adjusted.  PIM
   Assert metric and PIM Bidir DF metric if and only if all VRRP groups
   configured on an interface are in passive (non-Active) states to
   ensure that interfaces with all-passive VRRP groups will not win in
   DR, Assert and DF election.  In other words, DR, Assert, DF winner
   will be elected among the interfaces with at least one Active VRRP
   group.

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6.  Support of HSRP

   Although there are differences between VRRP and Hot Standby Router
   Protocol (HSRP) [RFC2281] including number of backup (standby)
   routers, virtual IP address and timer intervals, the proposed scheme
   can also enable HSRP aware PIM with similar failover and tracking
   mechanism described in this draft.

7.  Security Considerations

   The proposed tracking mechanism does not discuss adding
   authentication to the protocols and introduces no new negative impact
   or threats on security to PIM in either SSM or ASM mode.  Note that
   VRRP messages from malicious nodes could cause unexpected behaviors
   such as multiple Masters and PIM DRs which are associated with VRRP
   specific security issues.  Detailed analysis of PIM and VRRP security
   is provided in [RFC 5294] and [RFC 5798].

8.  IANA Considerations

   This document has no IANA actions.

9.  Acknowledgments

   I would like to give a special thank you and appreciation to Stig
   Venaas for his ideas and comments in this draft.

10.  Informative References

   [RFC2281]  Li, T., Cole, B., Morton, P., and D. Li, "Cisco Hot
              Standby Router Protocol (HSRP)", RFC 2281,
              DOI 10.17487/RFC2281, March 1998,
              <http://www.rfc-editor.org/info/rfc2281>.

   [RFC4601]  Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
              "Protocol Independent Multicast - Sparse Mode (PIM-SM):
              Protocol Specification (Revised)", RFC 4601,
              DOI 10.17487/RFC4601, August 2006,
              <http://www.rfc-editor.org/info/rfc4601>.

   [RFC5798]  Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP)
              Version 3 for IPv4 and IPv6", RFC 5798,
              DOI 10.17487/RFC5798, March 2010,
              <http://www.rfc-editor.org/info/rfc5798>.

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Author's Address

   Wei Zhou
   cisco Systems
   Tasman Drive
   San Jose, CA  95134
   USA

   Email: weizho2@cisco.com

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