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INTERNET-DRAFT                                          R. Hinden/Nokia
June 29, 2003



              Virtual Router Redundancy Protocol for IPv6

                   <draft-ietf-vrrp-ipv6-spec-05.txt>


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of [RFC2026].

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   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."

   To view the list Internet-Draft Shadow Directories, see
   http://www.ietf.org/shadow.html.

   This internet draft expires on January 4, 2004.

Abstract

   This memo defines the Virtual Router Redundancy Protocol (VRRP) for
   IPv6.  It is version three (3) of the protocol.  It is based on the
   original version of VRRP (version 2) for IPv4 that is defined in
   RFC2338.

   VRRP specifies an election protocol that dynamically assigns
   responsibility for a virtual router to one of the VRRP routers on a
   LAN.  The VRRP router controlling the IP address associated with a
   virtual router is called the Master, and forwards packets sent to
   this IP address.  The election process provides dynamic fail over in
   the forwarding responsibility should the Master become unavailable.
   The advantage gained from using VRRP for IPv6 is a quicker switch
   over to back up routers than can be obtained with standard IPv6
   Neighbor Discovery [ND] mechanisms.





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Table of Contents

   1. Introduction................................................3
   2. Required Features...........................................5
   3. VRRP Overview...............................................6
   4. Sample Configurations.......................................8
   5. Protocol...................................................10
      5.1  VRRP Packet Format....................................10
      5.2  IP Field Descriptions.................................10
      5.3  VRRP Field Descriptions...............................11
   6.  Protocol State Machine....................................13
      6.1  Parameters per Virtual Router.........................13
      6.2  Timers................................................14
      6.3  State Transition Diagram..............................14
      6.4  State Descriptions....................................14
   7.  Sending and Receiving VRRP Packets........................18
      7.1  Receiving VRRP Packets................................18
      7.2  Transmitting Packets..................................18
      7.3  Virtual MAC Address...................................19
      7.4  IPv6 Interface Identifiers............................19
   8.  Operational Issues........................................20
      8.1  ICMPv6 Redirects......................................20
      8.2  ND Neighbor Solicitation..............................20
      8.3  Potential Forwarding Loop.............................21
   9.  Operation over FDDI, Token Ring, and ATM LANE.............21
      9.1  Operation over FDDI...................................21
      9.2  Operation over Token Ring.............................21
      9.3  Operation over ATM LANE...............................23
   10. Security Considerations...................................24
   11. Acknowledgments...........................................24
   12. IANA Considerations.......................................24
   13. Normative References......................................25
   14. Informative References....................................26
   15. Authors' Address..........................................26
   16. Changes from RFC2338......................................26
















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1.  Introduction

   IPv6 hosts on a LAN will usually learn about one or more default
   routers by receiving Router Advertisements sent using the IPv6
   Neighbor Discovery protocol [ND].  The Router Advertisements are
   multicast periodically at a rate that the hosts will learn about the
   default routers in a few minutes. They are not sent frequently enough
   to rely on the absence of the router advertisement to detect router
   failures.

   Neighbor Discovery (ND) includes a mechanism called Neighbor
   Unreachability Detection to detect the failure of a neighbor node
   (router or host) or the forwarding path to a neighbor.  This is done
   by sending unicast ND Neighbor Solicitation messages to the neighbor
   node.  To reduce the overhead of sending Neighbor Solicitations, they
   are only sent to neighbors to which the node is actively sending
   traffic and only after there has been no positive indication that the
   router is up for a period of time.  Using the default parameters in
   ND, it will take a host about 38 seconds to learn that a router is
   unreachable before it will switch to another default router.  This
   delay would be very noticeable to users and cause some transport
   protocol implementations to timeout.

   While the ND unreachability detection could be speeded up by changing
   the parameters to be more aggressive (note that the current lower
   limit for this is 5 seconds), this would have the downside of
   significantly increasing the overhead of ND traffic.  Especially when
   there are many hosts all trying to determine the reachability of a
   one of more routers.

   The Virtual Router Redundancy Protocol for IPv6 provides a much
   faster switch over to an alternate default router than can be
   obtained using standard ND procedures.  Using VRRP a backup router
   can take over for a failed default router in around three seconds
   (using VRRP default parameters).  This is done with out any
   interaction with the hosts and a minimum amount of VRRP traffic.

   VRRP specifies an election protocol that dynamically assigns
   responsibility for a virtual router to one of the VRRP routers on a
   LAN.  The VRRP router controlling the IP address associated with a
   virtual router is called the Master, and forwards packets sent to
   this IP address.  The election process provides dynamic fail over in
   the forwarding responsibility should the Master become unavailable.

   VRRP provides a function similar to a Cisco Systems, Inc. proprietary
   protocol named Hot Standby Router Protocol (HSRP) [HSRP] and to a
   Digital Equipment Corporation, Inc. proprietary protocol named IP
   Standby Protocol [IPSTB].



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   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].

   The IESG/IETF take no position regarding the validity or scope of any
   intellectual property right or other rights that might be claimed to
   pertain to the implementation or use of the technology, or the extent
   to which any license under such rights might or might not be
   available.  See the IETF IPR web page at http://www.ietf.org/ipr.html
   for additional information.


1.1  Scope

   The remainder of this document describes the features, design goals,
   and theory of operation of VRRP for IPv6.  The message formats,
   protocol processing rules and state machine that guarantee
   convergence to a single Virtual Router Master are presented.
   Finally, operational issues related to MAC address mapping, handling
   of Neighbor Discovery requests, generation of ICMPv6 redirect
   messages, and security issues are addressed.

   This protocol is intended for use with IPv6 routers only.  VRRP for
   IPv4 is defined in [VRRP-V4].


1.2  Definitions

   VRRP Router            A router running the Virtual Router Redundancy
                          Protocol.  It may participate in one or more
                          virtual routers.

   Virtual Router         An abstract object managed by VRRP that acts
                          as a default router for hosts on a shared LAN.
                          It consists of a Virtual Router Identifier and
                          an IPv6 address across a common LAN.  A VRRP
                          Router may backup one or more virtual routers.

   IPv6 Address Owner     The VRRP router that has the virtual router's
                          IPv6 address as real interface address.  This
                          is the router that, when up, will respond to
                          packets addressed to the IPv6 addresses for
                          ICMPv6 pings, TCP connections, etc.

   Virtual Router Master  The VRRP router that is assuming the
                          responsibility of forwarding packets sent to
                          the IPv6 address associated with the virtual
                          router, and answering ND requests for this



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                          IPv6 address.  Note that if the IPv6 address
                          owner is available, then it will always become
                          the Master.

   Virtual Router Backup  The set of VRRP routers available to assume
                          forwarding responsibility for a virtual router
                          should the current Master fail.


2.0 Required Features

   This section outlines the set of features that were considered
   mandatory and that guided the design of VRRP.


2.1 IPv6 Address Backup

   Backup of an IPv6 address is the primary function of the Virtual
   Router Redundancy Protocol.  While providing election of a Virtual
   Router Master and the additional functionality described below, the
   protocol should strive to:

    - Minimize the duration of black holes.
    - Minimize the steady state bandwidth overhead and processing
      complexity.
    - Function over a wide variety of multiaccess LAN technologies
      capable of supporting IPv6 traffic.
    - Provide for election of multiple virtual routers on a network for
      load balancing
    - Support of multiple logical IPv6 subnets on a single LAN segment.


2.2 Preferred Path Indication

   A simple model of Master election among a set of redundant routers is
   to treat each router with equal preference and claim victory after
   converging to any router as Master.  However, there are likely to be
   many environments where there is a distinct preference (or range of
   preferences) among the set of redundant routers.  For example, this
   preference may be based upon access link cost or speed, router
   performance or reliability, or other policy considerations.  The
   protocol should allow the expression of this relative path preference
   in an intuitive manner, and guarantee Master convergence to the most
   preferential router currently available.







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2.3 Minimization of Unnecessary Service Disruptions

   Once Master election has been performed then any unnecessary
   transitions between Master and Backup routers can result in a
   disruption in service.  The protocol should ensure after Master
   election that no state transition is triggered by any Backup router
   of equal or lower preference as long as the Master continues to
   function properly.

   Some environments may find it beneficial to avoid the state
   transition triggered when a router becomes available that is more
   preferential than the current Master.  It may be useful to support an
   override of the immediate convergence to the preferred path.


2.4 Efficient Operation over Extended LANs

   Sending IPv6 packets on a multiaccess LAN requires mapping from an
   IPv6 address to a MAC address.  The use of the virtual router MAC
   address in an extended LAN employing learning bridges can have a
   significant effect on the bandwidth overhead of packets sent to the
   virtual router.  If the virtual router MAC address is never used as
   the source address in a link level frame then the station location is
   never learned, resulting in flooding of all packets sent to the
   virtual router.  To improve the efficiency in this environment the
   protocol should: 1) use the virtual router MAC as the source in a
   packet sent by the Master to trigger station learning; 2) trigger a
   message immediately after transitioning to Master to update the
   station learning; and 3) trigger periodic messages from the Master to
   maintain the station learning cache.


3.0 VRRP Overview

   VRRP specifies an election protocol to provide the virtual router
   function described earlier.  All protocol messaging is performed
   using IPv6 multicast datagrams, thus the protocol can operate over a
   variety of multiaccess LAN technologies supporting IPv6 multicast.
   Each VRRP virtual router has a single well-known MAC address
   allocated to it.  This document currently only details the mapping to
   networks using the IEEE 802 48-bit MAC address.  The virtual router
   MAC address is used as the source in all periodic VRRP messages sent
   by the Master router to enable bridge learning in an extended LAN.

   A virtual router is defined by its virtual router identifier (VRID)
   and an IPv6 address.  A VRRP router may associate a virtual router
   with its real address on an interface, and may also be configured
   with additional virtual router mappings and priority for virtual



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   routers it is willing to backup.  The mapping between VRID and its
   IPv6 address must be coordinated among all VRRP routers on a LAN.
   However, there is no restriction against reusing a VRID with a
   different address mapping on different LANs.  The scope of each
   virtual router is restricted to a single LAN.

   To minimize network traffic, only the Master for each virtual router
   sends periodic VRRP Advertisement messages.  A Backup router will not
   attempt to preempt the Master unless it has higher priority.  This
   eliminates service disruption unless a more preferred path becomes
   available.  It's also possible to administratively prohibit all
   preemption attempts.  The only exception is that a VRRP router will
   always become Master of any virtual router associated with address it
   owns.  If the Master becomes unavailable then the highest priority
   Backup will transition to Master after a short delay, providing a
   controlled transition of the virtual router responsibility with
   minimal service interruption.

   The VRRP protocol design provides rapid transition from Backup to
   Master to minimize service interruption, and incorporates
   optimizations that reduce protocol complexity while guaranteeing
   controlled Master transition for typical operational scenarios.  The
   optimizations result in an election protocol with minimal runtime
   state requirements, minimal active protocol states, and a single
   message type and sender.  The typical operational scenarios are
   defined to be two redundant routers and/or distinct path preferences
   among each router.  A side effect when these assumptions are violated
   (i.e., more than two redundant paths all with equal preference) is
   that duplicate packets may be forwarded for a brief period during
   Master election.  However, the typical scenario assumptions are
   likely to cover the vast majority of deployments, loss of the Master
   router is infrequent, and the expected duration in Master election
   convergence is quite small ( << 1 second ).  Thus the VRRP
   optimizations represent significant simplifications in the protocol
   design while incurring an insignificant probability of brief network
   degradation.















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4.  Sample Configurations

4.1  Sample Configuration 1

   The following figure shows a simple network with two VRRP routers
   implementing one virtual router.  Note that this example is provided
   to help understand the protocol, but is not expected to occur in
   actual practice.

             +-----------+      +-----------+
             |   Rtr1    |      |   Rtr2    |
             |(MR VRID=1)|      |(BR VRID=1)|
             |           |      |           |
     VRID=1  +-----------+      +-----------+
     IPv6 A -------->*            *<--------- IPv6 B
                     |            |
                     |            |
   ------------------+------------+-----+--------+--------+--------+--
                                        ^        ^        ^        ^
                                        |        |        |        |
                                     (IPv6 A) (IPv6 A) (IPv6 A) (IPv6 A)
                                        |        |        |        |
                                     +--+--+  +--+--+  +--+--+  +--+--+
                                     |  H1 |  |  H2 |  |  H3 |  |  H4 |
                                     +-----+  +-----+  +--+--+  +--+--+
      Legend:
               ---+---+---+--  =  Ethernet, Token Ring, or FDDI
                            H  =  Host computer
                           MR  =  Master Router
                           BR  =  Backup Router
                            *  =  IPv6 Address
                       (IPv6)  =  default router for hosts

   Eliminating all mention of VRRP (VRID=1) from the figure above leaves
   it as a typical IPv6 deployment.  Each router has a link-local IPv6
   address on the LAN interface (Rtr1 is assigned IPv6 Link-Local A and
   Rtr2 is assigned IPv6 Link-Local B), and each host learns a default
   route from Router Advertisements through one of the routers (in this
   example they all use Rtr1's IPv6 Link-Local A).

   Moving to the VRRP environment, each router has the exact same Link-
   Local IPv6 address.  Rtr1 is said to be the IPv6 address owner of
   IPv6 A, and Rtr2 is the IPv6 address owner of IPv6 B.  A virtual
   router is then defined by associating a unique identifier (the
   virtual router ID) with the address owned by a router.  Finally, the
   VRRP protocol manages virtual router fail over to a backup router.

   The example above shows a virtual router configured to cover the IPv6



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   address owned by Rtr1 (VRID=1,IPv6_Address=A).  When VRRP is enabled
   on Rtr1 for VRID=1 it will assert itself as Master, with
   priority=255, since it is the IPv6 address owner for the virtual
   router IPv6 address.  When VRRP is enabled on Rtr2 for VRID=1 it will
   transition to Backup, with priority=100, since it is not the IPv6
   address owner.  If Rtr1 should fail then the VRRP protocol will
   transition Rtr2 to Master, temporarily taking over forwarding
   responsibility for IPv6 A to provide uninterrupted service to the
   hosts.

   Note that in this example IPv6 B is not backed up, it is only used by
   Rtr2 as its interface address.  In order to backup IPv6 B, a second
   virtual router must be configured.  This is shown in the next
   section.


4.2  Sample Configuration 2

   The following figure shows a configuration with two virtual routers
   with the hosts splitting their traffic between them.  This example is
   expected to be common in actual practice.

             +-----------+      +-----------+
             |   Rtr1    |      |   Rtr2    |
             |(MR VRID=1)|      |(BR VRID=1)|
             |(BR VRID=2)|      |(MR VRID=2)|
     VRID=1  +-----------+      +-----------+  VRID=2
     IPv6 A -------->*            *<---------- IPv6 B
                     |            |
                     |            |
   ------------------+------------+-----+--------+--------+--------+--
                                        ^        ^        ^        ^
                                        |        |        |        |
                                     (IPv6 A) (IPv6 A) (IPv6 B) (IPv6 B)
                                        |        |        |        |
                                     +--+--+  +--+--+  +--+--+  +--+--+
                                     |  H1 |  |  H2 |  |  H3 |  |  H4 |
                                     +-----+  +-----+  +--+--+  +--+--+
      Legend:
               ---+---+---+--  =  Ethernet, Token Ring, or FDDI
                            H  =  Host computer
                           MR  =  Master Router
                           BR  =  Backup Router
                            *  =  IPv6 Address
                       (IPv6)  =  default router for hosts

   In the example above, half of the hosts have learned a default route
   through Rtr1's IPv6 A and half are using Rtr2's IPv6 B.  The



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   configuration of virtual router VRID=1 is exactly the same as in the
   first example (see section 4.1), and a second virtual router has been
   added to cover the IPv6 address owned by Rtr2 (VRID=2,
   IPv6_Address=B).  In this case Rtr2 will assert itself as Master for
   VRID=2 while Rtr1 will act as a backup.  This scenario demonstrates a
   deployment providing load splitting when both routers are available
   while providing full redundancy for robustness.


5.0  Protocol

   The purpose of the VRRP packet is to communicate to all VRRP routers
   the priority and the state of the Master router associated with the
   Virtual Router ID.

   VRRP packets are sent encapsulated in IPv6 packets.  They are sent to
   the IPv6 multicast address assigned to VRRP.


5.1  VRRP Packet Format

   This section defines the format of the VRRP packet and the relevant
   fields in the IPv6 header.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |Version| Type  | Virtual Rtr ID|   Priority    |   (reserved)  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  (reserved)   |   Adver Int   |          Checksum             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                                                               +
      |                                                               |
      +                         IPv6 Address                          +
      |                                                               |
      +                                                               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



5.2  IPv6 Field Descriptions

5.2.1  Source Address

   The IPv6 link-local address of the interface the packet is being sent
   from.



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5.2.2  Destination Address

   The IPv6 multicast address as assigned by the IANA for VRRP is:

       FF02:0:0:0:0:0:XXXX:XXXX

   This is a link-local scope multicast address.  Routers MUST NOT
   forward a datagram with this destination address regardless of its
   Hop Limit.

5.2.3  Hop Limit

   The Hop Limit MUST be set to 255.  A VRRP router receiving a packet
   with the Hop Limit not equal to 255 MUST discard the packet.

5.2.4  Next Header

   The IPv6 Next Header protocol assigned by the IANA for VRRP is 112
   (decimal).


5.3 VRRP Field Descriptions

5.3.1  Version

   The version field specifies the VRRP protocol version of this packet.
   This document defines version 3.

5.3.2  Type

   The type field specifies the type of this VRRP packet.  The only
   packet type defined in this version of the protocol is:

       1      ADVERTISEMENT

   A packet with unknown type MUST be discarded.

5.3.3  Virtual Rtr ID (VRID)

   The Virtual Router Identifier (VRID) field identifies the virtual
   router this packet is reporting status for.

5.3.4  Priority

   The priority field specifies the sending VRRP router's priority for
   the virtual router.  Higher values equal higher priority.  This field
   is an 8 bit unsigned integer field.




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   The priority value for the VRRP router that owns the IPv6 address
   associated with the virtual router MUST be 255 (decimal).

   VRRP routers backing up a virtual router MUST use priority values
   between 1-254 (decimal).  The default priority value for VRRP routers
   backing up a virtual router is 100 (decimal).

   The priority value zero (0) has special meaning indicating that the
   current Master has stopped participating in VRRP.  This is used to
   trigger Backup routers to quickly transition to Master without having
   to wait for the current Master to timeout.

5.3.5  Reserved

   This field MUST be set to zero on transmission and ignored on
   reception.

5.3.5  Reserved

   This field MUST be set to zero on transmission and ignored on
   reception.

5.3.6 Advertisement Interval (Adver Int)

   The Advertisement interval indicates the time interval (in seconds)
   between ADVERTISEMENTS.  The default is 1 second.  This field is used
   for troubleshooting misconfigured routers.

5.3.7 Checksum

   The checksum field is used to detect data corruption in the VRRP
   message.

   The checksum is the 16-bit one's complement of the one's complement
   sum of the entire VRRP message starting with the version field and a
   "pseudo-header" as defined in section 8.1 of RFC2460 [IPv6].  The
   next header field in the "pseudo-header" should be set to 112
   (decimal) for VRRP.  For computing the checksum, the checksum field
   is set to zero.  See RFC1071 for more detail [CKSM].

5.3.8  IPv6 Address

   The IPv6 link-local address associated with the virtual router.








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6.  Protocol State Machine

6.1 Parameters per Virtual Router

    VRID                    Virtual Router Identifier.  Configured item
                            in the range 1-255 (decimal).  There is no
                            default.

    Priority                Priority value to be used by this VRRP
                            router in Master election for this virtual
                            router.  The value of 255 (decimal) is
                            reserved for the router that owns the IPv6
                            address associated with the virtual router.
                            The value of 0 (zero) is reserved for Master
                            router to indicate it is releasing
                            responsibility for the virtual router.  The
                            range 1-254 (decimal) is available for VRRP
                            routers backing up the virtual router.  The
                            default value is 100 (decimal).

    IPv6_Address            The IPv6 link-local address associated with
                            this virtual router.  Configured item.  No
                            default.

    Advertisement_Interval  Time interval between ADVERTISEMENTS
                            (seconds).  Default is 1 second.

    Skew_Time               Time to skew Master_Down_Interval in
                            seconds.  Calculated as:

                               ( (256 - Priority) / 256 )

    Master_Down_Interval    Time interval for Backup to declare Master
                            down (seconds).  Calculated as:

                               (3 * Advertisement_Interval) + Skew_time

    Preempt_Mode            Controls whether a higher priority Backup
                            router preempts a lower priority Master.
                            Values are True to allow preemption and
                            False to prohibit preemption.  Default is
                            True.

                            Note: Exception is that the router that owns
                            the IPv6 address associated with the virtual
                            router always preempts independent of the
                            setting of this flag.




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6.2 Timers

    Master_Down_Timer       Timer that fires when ADVERTISEMENT has not
                            been heard for Master_Down_Interval.

    Adver_Timer             Timer that fires to trigger sending of
                            ADVERTISEMENT based on
                            Advertisement_Interval.



6.3  State Transition Diagram

                          +---------------+
               +--------->|               |<-------------+
               |          |  Initialize   |              |
               |   +------|               |----------+   |
               |   |      +---------------+          |   |
               |   |                                 |   |
               |   V                                 V   |
       +---------------+                       +---------------+
       |               |---------------------->|               |
       |    Master     |                       |    Backup     |
       |               |<----------------------|               |
       +---------------+                       +---------------+


6.4  State Descriptions

   In the state descriptions below, the state names are identified by
   {state-name}, and the packets are identified by all upper case
   characters.

   A VRRP router implements an instance of the state machine for each
   virtual router election it is participating in.

6.4.1   Initialize

   The purpose of this state is to wait for a Startup event.  If a
   Startup event is received, then:

    - If the Priority = 255 (i.e., the router owns the IPv6 address
      associated with the virtual router)

       o Send an ADVERTISEMENT
       o Send an unsolicited ND Neighbor Advertisement with the Router
         Flag (R) set, the Solicited Flag (S) unset, the Override flag
         (O) set, the Target Address set to the IPv6 link-local address



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         of the Virtual Router, and the Target Link Layer address set to
         the virtual router MAC address.
       o Set the Adver_Timer to Advertisement_Interval
       o Transition to the {Master} state

      else

       o Set the Master_Down_Timer to Master_Down_Interval
       o Transition to the {Backup} state

      endif

6.4.2   Backup

   The purpose of the {Backup} state is to monitor the availability and
   state of the Master Router.

   While in this state, a VRRP router MUST do the following:

    - MUST NOT respond to ND Neighbor Solicitation messages for the IPv6
      address associated with the virtual router.

    - MUST NOT send ND Router Advertisement messages for the virtual
      router.

    - MUST discard packets with a destination link layer MAC address
      equal to the virtual router MAC address.

    - MUST NOT accept packets addressed to the IPv6 address associated
      with the virtual router.

    - If a Shutdown event is received, then:

       o Cancel the Master_Down_Timer
       o Transition to the {Initialize} state

      endif

    - If the Master_Down_Timer fires, then:

       o Send an ADVERTISEMENT
       o Compute and join the Solicited-Node multicast address [ADD-ARH]
         for the link-local IPv6 address of the Virtual Router.
       o Send an unsolicited ND Neighbor Advertisement with the Router
         Flag (R) set, the Solicited Flag (S) unset, the Override flag
         (O) set, the Target Address set to the IPv6 link-local address
         of the Virtual Router, and the Target Link Layer address set to
         the virtual router MAC address.



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       o Set the Adver_Timer to Advertisement_Interval
       o Transition to the {Master} state

      endif

    - If an ADVERTISEMENT is received, then:

         If the Priority in the ADVERTISEMENT is Zero, then:

          o Set the Master_Down_Timer to Skew_Time

         else:

            If Preempt_Mode is False, or If the Priority in the
            ADVERTISEMENT is greater than or equal to the local
            Priority, then:

             o Reset the Master_Down_Timer to Master_Down_Interval

            else:

             o Discard the ADVERTISEMENT

            endif
         endif
      endif

6.4.3   Master

   While in the {Master} state the router functions as the forwarding
   router for the IPv6 address associated with the virtual router.

   While in this state, a VRRP router MUST do the following:

    - MUST be a member of the Solicited-Node multicast address for the
      IPv6 link-local address associated with the virtual router.

    - MUST respond to ND Neighbor Solicitation message for the IPv6
      address associated with the virtual router.

    - MUST send ND Router Advertisements for the virtual router.

    - MUST respond to ND Router Solicitation message for the virtual
      router.

    - MUST forward packets with a destination link layer MAC address
      equal to the virtual router MAC address.




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    - MUST NOT accept packets addressed to the IPv6 address associated
      with the virtual router if it is not the IPv6 address owner.

    - MUST accept packets addressed to the IPv6 address associated with
      the virtual router if it is the IPv6 address owner.

    - If a Shutdown event is received, then:

       o Cancel the Adver_Timer
       o Send an ADVERTISEMENT with Priority = 0
       o Transition to the {Initialize} state

      endif

    - If the Adver_Timer fires, then:

       o Send an ADVERTISEMENT
       o Reset the Adver_Timer to Advertisement_Interval

      endif

    - If an ADVERTISEMENT is received, then:

         If the Priority in the ADVERTISEMENT is Zero, then:

          o Send an ADVERTISEMENT
          o Reset the Adver_Timer to Advertisement_Interval

         else:

            If the Priority in the ADVERTISEMENT is greater than the
            local Priority,
            or
            If the Priority in the ADVERTISEMENT is equal to the local
            Priority and the IPv6 Address of the sender is greater than
            the local IPv6 Address, then:

             o Cancel Adver_Timer
             o Set Master_Down_Timer to Master_Down_Interval
             o Transition to the {Backup} state

            else:

             o Discard ADVERTISEMENT

            endif
         endif
      endif



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7.  Sending and Receiving VRRP Packets

7.1  Receiving VRRP Packets

   Performed the following functions when a VRRP packet is received:

      - MUST verify that the IPv6 Hop Limit is 255.
      - MUST verify the VRRP version is 3
      - MUST verify that the received packet contains the complete VRRP
        packet (including fixed fields, and IPv6 Address.
      - MUST verify the VRRP checksum
      - MUST verify that the VRID is configured on the receiving
        interface and the local router is not the IPv6 Address owner
        (Priority equals 255 (decimal)).

   If any one of the above checks fails, the receiver MUST discard the
   packet, SHOULD log the event and SHOULD indicate via network
   management that an error occurred.

      - MAY verify that the IPv6 Address matches the IPv6_Address
        configured for the VRID.

   If the above check fails, the receiver SHOULD log the event and
   SHOULD indicate via network management that a misconfiguration was
   detected.  If the packet was not generated by the address owner
   (Priority does not equal 255 (decimal)), the receiver MUST drop the
   packet, otherwise continue processing.

      - MUST verify that the Adver Interval in the packet is the same as
        the locally configured for this virtual router

   If the above check fails, the receiver MUST discard the packet,
   SHOULD log the event and SHOULD indicate via network management that
   a misconfiguration was detected.


7.2 Transmitting VRRP Packets

   The following operations MUST be performed when transmitting a VRRP
   packet.

      - Fill in the VRRP packet fields with the appropriate virtual
        router configuration state
      - Compute the VRRP checksum
      - Set the source MAC address to Virtual Router MAC Address
      - Set the source IPv6 address to interface link-local IPv6 address
      - Set the IPv6 protocol to VRRP
      - Send the VRRP packet to the VRRP IP multicast group



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   Note: VRRP packets are transmitted with the virtual router MAC
   address as the source MAC address to ensure that learning bridges
   correctly determine the LAN segment the virtual router is attached
   to.


7.3 Virtual Router MAC Address

   The virtual router MAC address associated with a virtual router is an
   IEEE 802 MAC Address in the following format:

      00-00-5E-00-02-{VRID} (in hex in internet standard bit-order)

   The first three octets are derived from the IANA's OUI.  The next two
   octets (00-02) indicate the address block assigned to the VRRP for
   IPv6 protocol.  {VRID} is the VRRP Virtual Router Identifier.  This
   mapping provides for up to 255 VRRP routers on a network.


7.4 IPv6 Interface Identifiers

   IPv6 Routers running VRRP MUST create their Interface Identifiers in
   the normal manner (e.g., RFC2464 "Transmission of IPv6 Packets over
   Ethernet").  They MUST NOT use the Virtual Router MAC address to
   create the Modified EUI-64 identifiers.

   This VRRP specification describes how to advertise and resolve the
   VRRP routers IPv6 link local address into the Virtual Router MAC
   address.






















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8.  Operational Issues

8.1 ICMPv6 Redirects

   ICMPv6 Redirects may be used normally when VRRP is running between a
   group of routers [ICMPv6].  This allows VRRP to be used in
   environments where the topology is not symmetric (e.g., the VRRP
   routers do not connect to the same destinations).

   The IPv6 source address of an ICMPv6 redirect should be the address
   the end host used when making its next hop routing decision.  If a
   VRRP router is acting as Master for virtual router(s) containing
   addresses it does not own, then it must determine which virtual
   router the packet was sent to when selecting the redirect source
   address.  One method to deduce the virtual router used is to examine
   the destination MAC address in the packet that triggered the
   redirect.


8.2  ND Neighbor Solicitation

   When a host sends an ND Neighbor Solicitation message for the virtual
   router IPv6 address, the Master virtual router MUST respond to the ND
   Neighbor Solicitation message with the virtual MAC address for the
   virtual router.  The Master virtual router MUST NOT respond with its
   physical MAC address.  This allows the client to always use the same
   MAC address regardless of the current Master router.

   When a Master virtual router sends an ND Neighbor Solicitation
   message for a host's IPv6 address, the Master virtual router MUST
   include the virtual MAC address for the virtual router if it sends a
   source link-layer address option in the neighbor solicitation
   message.  It MUST NOT use its physical MAC address in the source
   link-layer address option.

   When a VRRP router restarts or boots, it SHOULD not send any ND
   messages with its physical MAC address for the IPv6 address it owns,
   it should only send ND messages that include Virtual MAC addresses.
   This may entail:

    - When configuring an interface, VRRP routers should send an
      unsolicitated ND Neighbor Advertisement message containing the
      virtual router MAC address for the IPv6 address on that interface.

    - At system boot, when initializing interfaces for VRRP operation;
      delay all ND Router and Neighbor Advertisements and Solicitation
      messages until both the IPv6 address and the virtual router MAC
      address are configured.



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8.3 Potential Forwarding Loop

   A VRRP router SHOULD not forward packets addressed to the IPv6
   Address it becomes Master for if it is not the owner.  Forwarding
   these packets would result in unnecessary traffic.  Also in the case
   of LANs that receive packets they transmit (e.g., token ring) this
   can result in a forwarding loop that is only terminated when the IPv6
   TTL expires.

   One such mechanism for VRRP routers is to add/delete a reject host
   route for each adopted IPv6 address when transitioning to/from MASTER
   state.


9.  Operation over FDDI, Token Ring, and ATM LANE

9.1 Operation over FDDI

   FDDI interfaces remove from the FDDI ring frames that have a source
   MAC address matching the device's hardware address.  Under some
   conditions, such as router isolations, ring failures, protocol
   transitions, etc., VRRP may cause there to be more than one Master
   router.  If a Master router installs the virtual router MAC address
   as the hardware address on a FDDI device, then other Masters'
   ADVERTISEMENTS will be removed from the ring during the Master
   convergence, and convergence will fail.

   To avoid this an implementation SHOULD configure the virtual router
   MAC address by adding a unicast MAC filter in the FDDI device, rather
   than changing its hardware MAC address.  This will prevent a Master
   router from removing any ADVERTISEMENTS it did not originate.


9.2  Operation over Token Ring

   Token ring has several characteristics that make running VRRP
   difficult. These include:

    - In order to switch to a new master located on a different bridge
      token ring segment from the previous master when using source
      route bridges, a mechanism is required to update cached source
      route information.

    - No general multicast mechanism supported across old and new token
      ring adapter implementations. While many newer token ring adapters
      support group addresses, token ring functional address support is
      the only generally available multicast mechanism. Due to the
      limited number of token ring functional addresses these may



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      collide with other usage of the same token ring functional
      addresses.

   Due to these difficulties, the preferred mode of operation over token
   ring will be to use a token ring functional address for the VRID
   virtual MAC address. Token ring functional addresses have the two
   high order bits in the first MAC address octet set to B'1'.  They
   range from 03-00-00-00-00-80 to 03-00-02-00-00-00 (canonical format).
   However, unlike multicast addresses, there is only one unique
   functional address per bit position. The functional addresses
   addresses  03-00-00-10-00-00 through 03-00-02-00-00-00 are reserved
   by the Token Ring Architecture [TKARCH] for user-defined
   applications.  However, since there are only 12 user-defined token
   ring functional addresses, there may be other non-IP protocols using
   the same functional address. Since the Novell IPX [IPX] protocol uses
   the 03-00-00-10-00-00 functional address, operation of VRRP over
   token ring will avoid use of this functional address. In general,
   token ring VRRP users will be responsible for resolution of other
   user-defined token ring functional address conflicts.

   VRIDs are mapped directly to token ring functional addresses. In
   order to decrease the likelihood of functional address conflicts,
   allocation will begin with the largest functional address. Most non-
   IP protocols use the first or first couple user-defined functional
   addresses and it is expected that VRRP users will choose VRIDs
   sequentially starting with 1.

      VRID      Token Ring Functional Address
      ----      -----------------------------
         1             03-00-02-00-00-00
         2             03-00-04-00-00-00
         3             03-00-08-00-00-00
         4             03-00-10-00-00-00
         5             03-00-20-00-00-00
         6             03-00-40-00-00-00
         7             03-00-80-00-00-00
         8             03-00-00-01-00-00
         9             03-00-00-02-00-00
        10             03-00-00-04-00-00
        11             03-00-00-08-00-00

   Or more succinctly, octets 3 and 4 of the functional address are
   equal to (0x4000 >> (VRID - 1)) in non-canonical format.

   Since a functional address cannot be used used as a MAC level source
   address, the real MAC address is used as the MAC source address in
   VRRP advertisements. This is not a problem for bridges since packets
   addressed to functional addresses will be sent on the spanning-tree



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   explorer path [802.1D].

   The functional address mode of operation MUST be implemented by
   routers supporting VRRP on token ring.

   Additionally, routers MAY support unicast mode of operation to take
   advantage of newer token ring adapter implementations that support
   non-promiscuous reception for multiple unicast MAC addresses and to
   avoid both the multicast traffic and usage conflicts associated with
   the use of token ring functional addresses. Unicast mode uses the
   same mapping of VRIDs to virtual MAC addresses as Ethernet.  However,
   one important difference exists. ND request/reply packets contain the
   virtual MAC address as the source MAC address. The reason for this is
   that some token ring driver implementations keep a cache of MAC
   address/source routing information independent of the ND cache.
   Hence, these implementations need have to receive a packet with the
   virtual MAC address as the source address in order to transmit to
   that MAC address in a source-route bridged network.

   Unicast mode on token ring has one limitation that should be
   considered.  If there are VRID routers on different source-route
   bridge segments and there are host implementations that keep their
   source-route information in the ND cache and do not listen to
   gratuitous NDs, these hosts will not update their ND source-route
   information correctly when a switch-over occurs. The only possible
   solution is to put all routers with the same VRID on the same source-
   bridge segment and use techniques to prevent that bridge segment from
   being a single point of failure. These techniques are beyond the
   scope this document.

   For both the multicast and unicast mode of operation, VRRP
   advertisements sent to 224.0.0.18 should be encapsulated as described
   in [RFC1469].


9.3  Operation over ATM LANE

   Operation of VRRP over ATM LANE on routers with ATM LANE interfaces
   and/or routers behind proxy LEC's are beyond the scope of this
   document.


10. Security Considerations

   VRRP for IPv6 does not include any type of authentication.  Earlier
   versions of VRRP for IPv4 specification included several types of
   authentication ranging from none to strong [VRRP-V4].




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   Operational experience and further analysis determined that these did
   not provide any real measure of security and do to the nature of the
   VRRP protocol they did not prevent incorrectly configured or hostile
   routers from becoming VRRP masters.  In general on LANs any device on
   the LAN has the ability to disrupt all communication.  For example
   although securing VRRP prevents unauthorized machines from taking
   part in the election protocol, it does not protect hosts on the
   network from being deceived.  A gratuitous ND reply from what
   purports to be the virtual router's IPv6 address can redirect traffic
   to an unauthorized machine.  Similarly, individual connections can be
   diverted by means of forged ICMPv6 Redirect messages. Consequentially
   it was determined it was better to remove the additional
   authentication methods in this specification of the VRRP protocol as
   it did not provide the authentication originally intended.

   VRRP includes a mechanism (setting TTL=255, checking on receipt) that
   protects against VRRP packets being injected from another remote
   network.  This limits most vulnerabilities to local attacks.

   VRRP does not provide any confidentiality.  Confidentiality is not
   necessary for the correct operation of VRRP and there is no
   information in the VRRP messages that must be kept secret from other
   nodes on the LAN.


11. Acknowledgments

   This specification is based on RFC2238.  The authors of RFC2238 are
   S. Knight, D. Weaver, D. Whipple, R. Hinden, D. Mitzel, P. Hunt, P.
   Higginson, M. Shand, and A. Lindem.

   The author of this document would also like to thank Erik Nordmark,
   Thomas Narten, Steve Deering, Radia Perlman, and Danny Mitzel for
   their helpful suggestions.


12. IANA Considerations

   VRRP for IPv6 needs an IPv6 link-local scope multicast address
   assigned by the IANA for this specification.  The IPv6 multicast
   address should be of the following form:

       FF02:0:0:0:0:0:XXXX:XXXX

   The values assigned address should be entered into section 5.2.2.

   A convenient assignment of this link-local scope multicast would be:




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       FF02:0:0:0:0:0:0:12

   as this would be consistent with the IPv4 assignment for VRRP.

   The IANA should also reserve a block of IANA Ethernet unicast
   addresses from:

      00-00-5E-00-02-00  to  00-00-5E-00-02-FF  in hex

   for VRRP for IPv6.  Similar assignments are documented in:

       http://www.iana.org/assignments/ethernet-numbers


13.  Normative References

   [802.1D]  International Standard ISO/IEC 10038: 1993, ANSI/IEEE Std
             802.1D, 1993 edition.

   [ADD-ARH] Hinden, R., S. Deering, "IP Version 6 Addressing
             Architecture", RFC3513, April 2003.

   [CKSM]    Braden, R., D. Borman, C. Partridge, "Computing the
             Internet Checksum", RFC1071, September 1988.

   [ICMPv6]  Conta, A., S. Deering, "Internet Control Message Protocol
             (ICMPv6) for the Internet Protocol Version 6 (IPv6)",
             RFC2463, December 1998.

   [IPv6]    Deering, S., R. Hinden, "Internet Protocol, Version 6
             (IPv6) Specification", RFC2460, December 1998.

   [IPX]     Novell Incorporated., "IPX Router Specification", Version
             1.10, October 1992.

   [ND]      Narten, T., E. Nordmark, W. Simpson, "Neighbor Discovery
             for IP Version 6 (IPv6)", RFC2461, December 1998.

   [RFC1469] Pusateri, T., "IP Multicast over Token Ring Local Area
             Networks", RFC1469, June 1993.

   [RFC2026] Bradner, S., "The Internet Standards Process -- Revision
             3", RFC2026, BCP00009, October 1996.

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", RFC2119, BCP0014, March 1997.

   [TKARCH]  IBM Token-Ring Network, Architecture Reference, Publication



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             SC30-3374-02, Third Edition, (September, 1989).

   [VRRP-V4] Knight, S., et. al., "Virtual Router Redundancy Protocol",
             RFC2338, April 1998.


14.  Informative References

   [HSRP]    Li, T., B. Cole, P. Morton, D. Li, "Cisco Hot Standby
             Router Protocol (HSRP)", RFC2281, March 1998.

   [IPSTB]   Higginson, P., M. Shand, "Development of Router Clusters to
             Provide Fast Failover in IP Networks", Digital Technical
             Journal, Volume 9 Number 3, Winter 1997.

   [OSPF]    Moy, J., "OSPF version 2", RFC2328, STD0054, April 1998.

   [RIP]     Malkin, G., "RIP Version 2", RFC2453, STD0056, November
             1998.


15. Author's Address

   Robert Hinden
   Nokia
   313 Fairchild Drive
   Mountain View, CA 94043
   USA

   Phone: +1 650 625-2004
   EMail: hinden@iprg.nokia.com


16. Changes from RFC2338

    - Changed VMAC assignements to a separate block of IANA Ethernet
      addresses and added this to the IANA considerations section.
    - Removed different authentication methods, header fields, and
      updated the security considerations section.
    - General rewrite to change protocol to provide virtual router
      functionality from IPv4 to IPv6.  Specific changes include:
       o Increment VRRP version to 3.
       o Change packet format to support an 128-bit IPv6 address.
       o Change to only support one router address (instead of multiple
         addresses).  This included removing address count field from
         header.
       o Rewrote text to specify IPv6 Neighbor Discovery mechanisms
         instead of ARP.



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       o Changed state machine actions to use Neighbor Discovery
         mechanisms.  This includes sending unsolicited Neighbor
         Advertisements, Receiving Neighbor Solicitations, joining the
         appropriate solicited node multicast group, sending Router
         Advertisements, and receiving Router Solicitations.
    - Revised the section 4 examples text with a clearer description of
      mapping of IPv6 address owner, priorities, etc.
    - Clarify the section 7.1 text describing address list validation.
    - Corrected text in Preempt_Mode definition.
    - Changed authentication to be per Virtual Router instead of per
      Interface.
    - Added new subsection (9.3) stating that VRRP over ATM LANE is
      beyond the scope of this document.
    - Clarified text describing received packet length check.
    - Clarified text describing received authentication check.
    - Clarified text describing VRID verification check.
    - Added new subsection (8.4) describing need to not forward packets
      for adopted IPv6 addresses.
    - Added clarification to the security considerations section.
    - Added reference for computing the internet checksum.
    - Updated references and author information.
    - Removed IPR section as no IPR claims have been made against this
      draft.




























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