INTERNET-DRAFT                                                 S. Knight
June 22,
July 28, 1997                                Ascend Communications, Inc.                                                  D. Weaver
                                             Ascend Communications, Inc.
                                                              D. Whipple
                                                         Microsoft, Inc.
                                                               R. Hinden
                                                               D. Mitzel
                                                  Ipsilon Networks, Inc.

                   Virtual Router Redundancy Protocol

                     <draft-ietf-vrrp-spec-00.txt>

                     <draft-ietf-vrrp-spec-01.txt>

Status of this Memo

   This document is an Internet-Draft.  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
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   To learn the current status of any Internet-Draft, please check the
   ``1id-abstracts.txt''
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   Rim).

   This internet draft expires on December 23, 1997. January 29, 1998.

Abstract

   The

   This memo documents defines the Virtual Router Redundancy Protocol.  This is a Protocol (VRRP).
   VRRP specifies an election protocol which allows several routers that dynamically assigns
   responsibility for a virtual IP address to a single router among a
   collection of VRRP routers.  The VRRP router controlling the virtual
   IP address is called the Master router, and forwards packets sent to utilize
   the same virtual IP address.  One router will be elected as a master, with X routers
   acting as backups  The election process provides dynamic fail
   over in case of failure of the master router. forwarding responsibility should the Master become
   unavailable.  The
   primary advantage to utilizing this protocol, is that host systems
   may virtual IP address can then be configured with a single used as the default gateway, rather than running
   an active routing protocol.  Each interface on each
   first hop router within a
   VRRP cluster, will be configured with a real IP address, and by end-hosts.  The advantage gained from using the
   VRRP virtual IP address for is a higher availability default path without
   requiring configuration of dynamic routing or router discovery
   protocols on every end-host.

   This memo describes the particular cluster.  Overall, this features and theory of operation of VRRP.
   The protocol adds processing and state machine that guarantee convergence
   to the options for providing fault redundancy for a single Master router networks. is presented.  Also issues related to MAC
   address mapping, handling ARP requests, generating ICMP redirects,
   and security issues are addressed.

Table Of of Contents

   1.  Introduction...............................................3
   2.  Scope......................................................3  Scope......................................................4
   3.  Definitions................................................4  Definitions................................................6
   4.  Sample Configurations......................................4 Configurations......................................8
      4.1   Sample Configuration 1................................4 1................................8
      4.2   Sample Configuration 2................................5 2................................9
   5.  Protocol...................................................6  Protocol..................................................10
      5.1   VRRP Packet Format....................................6 Format...................................10
      5.2   IP Field Descriptions.................................6 Descriptions................................10
      5.3   VRRP Field Descriptions...............................7 Descriptions..............................11
   6.  Protocol State Machine.....................................9 Machine....................................14
      6.1 Parameters..............................................9 Parameters.............................................14
      6.2 Timers.................................................10 Timers.................................................14
      6.3  State Transition Diagram..............................10 Diagram..............................15
      6.4  State Descriptions....................................10
      6.5  State Table...........................................12 Descriptions....................................15
   7.  Sending and Receiving VRRP Packets........................14 Packets........................18
      7.1  Receiving VRRP Packets................................14 Packets................................18
      7.2 Transmitting Packets...................................14 Packets...................................18
      7.3 Virtual MAC Address....................................15 Address....................................19
   8.  Host Operation............................................15 Operation............................................19
      8.1   Host ARP Requests....................................15 Requests....................................19
   9.  Operational Issues........................................15 Issues........................................19
      9.1 ICMP Redirects.........................................15 Redirects.........................................19
      9.2 Proxy ARP..............................................15 ARP..............................................19
      9.3 Network Management.....................................16 Management.....................................19
   10.  Operation over FDDI and Token Ring.................................16 Ring.......................20
   11. References................................................17
   12. Security Considerations...................................17 Considerations...................................21
      11.1 No Authentication.....................................21
      11.2 Simple Text Password..................................21
      11.3 IP Authentication Header..............................21
   12. References................................................23
   13. Authors' Addresses........................................17 Addresses........................................23
   14. Acknowledgments...........................................17 Acknowledgments...........................................24
   15. Changes from Previous Drafts..............................18 Drafts..............................25

1.  Introduction

   The reason for the development of VRRP is to create

   There are a standard
   protocol, with multi-vendor support to resolve the problem number of methods that an end-host can use to determine
   its first hop router
   failure.  Specifically, when towards a single router is utilized particular IP destination.  These
   include running (or snooping) a dynamic routing protocol such as
   Routing Information Protocol [RIP] or OSPF version 2 [OSPF], running
   an ICMP router discovery client [DISC] or using a default
   gateway, and all hosts are statically
   configured to this default
   gateway, route.

   Running a failure is catastrophic.  VRRP resolves this problem by
   creating virtual clusters, where each cluster is configured with dynamic routing protocol on every end-host may be
   infeasible for a
   set number of reasons, including administrative
   overhead, processing overhead, security issues, or lack of member routers.  Each member router is either a master router protocol
   implementation for the cluster some platforms.  Neighbor or a backup router for discovery
   protocols may require active participation by all hosts on a network,
   leading to large timer values to reduce protocol overhead in the cluster, but not both
   simultaneously. In addition, there MUST only be face
   of large numbers of hosts.  This can result in a significant delay in
   the detection of a lost (i.e., dead) neighbor, which may introduce
   unacceptably long "black hole" periods.

   The use of a statically configured default route is quite popular; it
   minimizes configuration and processing overhead on the end-host and
   is supported by virtually every IP implementation.  This mode of
   operation is likely to persist as dynamic host configuration
   protocols [DHCP] are deployed, which typically provide configuration
   for an end-host IP address and default gateway.  However, this
   creates a single master point of failure.  Loss of the default router per cluster, at any given time. All member routers
   results in a catastrophic event, isolating all end-hosts that are
   configured
   unable to detect any alternate path that may be part available.

   The Virtual Router Redundancy Protocol (VRRP) is designed to
   eliminate the single point of failure inherent in the static default
   routed environment.  VRRP specifies an election protocol that
   dynamically assigns responsibility for a cluster, with a given virtual IP address.
   This address to a
   single router among a collection of VRRP routers.  The VRRP router
   controlling the virtual IP address is utilized as called the default gateway on all of Master router, and
   forwards packets sent to the host systems.  Given a failure on virtual IP address.  The election
   process provides dynamic fail-over in the current master router, forwarding responsibility
   should the
   next appropriate backup router will Master become unavailable.  The virtual IP address can
   then be used as the master default first hop router for the
   given cluster.  When routers are configured with the equal priority by end-hosts.  The
   advantage gained from using the router which is master will stay master as long as it VRRP virtual IP address is up.

   Of course this problem could be solved by running a standard higher
   availability default path without requiring configuration of dynamic
   routing
   protocol such as OSPF, RIP, or RIPv2 router discovery protocols on the hosts.  However, this is
   not always feasible due every end-host.

   VRRP provides a function similar to either security issues, when hosts are
   multihomed, or in some cases implementations of these routing
   protocols simply do not exist. a Cisco Systems, Inc. proprietary
   protocol named Hot Standby Router Protocol (HSRP) [HSRP].

   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].

2.

1.1  Scope

   This memo

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

   This protocol is intended for use with IPv4 routers only.  A version for IPv6 separate
   specification will be
   defined produced if it is decided that similar
   functionality is desirable in an IPv6 environment.

1.2  Definitions

   Cluster         The set of routers participating in VRRP to emulate a separate specification.

   Within
                   virtual router.

   Master Router   The VRRP router controlling the scope of this specification are:

      1.  Packet format and header contents.
      2.  State Diagrams virtual IP address
                   and Descriptions
      3.  Network Design Samples

   Outside of assuming the scope are

      1.  Network management
      2.  Host internal optimizations

3.  Definitions

   Cluster

      Used responsibility of forwarding packets
                   sent to describe a the virtual router.

   Backup Router   The set of routers who all have membership in the quiescent state with regard
                   to the virtual router operation.  This set of routers S, where S contains includes
                   all active VRRP routers configured with within a cluster that are not
                   the same virtual IP address. Master Router

      Used to describe router.

2.0 Required Features

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

2.1 Virtual IP Management

   Management of the currently active router, for a particular
      cluster, with a particular virtual IP address.  Their can only be
      one master address is the primary function of the
   virtual router in a particular cluster.

   Backup Router

      Used to describe protocol.  While providing election of a Master router which is configured to act as
   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 backup wide variety of multiaccess LAN technologies
      capable of supporting IP traffic.
    - Provide for a particular cluster.  There can be several backup election of multiple virtual routers on a network for
      load balancing or in support of multiple logical IP subnets on a
      single cluster.

4.  Sample Configurations

4.1  Sample Configuration 1

   The following figure shows a LAN segment.

2.2 Preferred Path Indication

   A simple VRRP network.

                       +--------------------------+
                       |        Cluster X         |
                       |                          |
                       |   +-----+      +-----+   |
                       |   | MRX |      | BRX |   |
                       |   +-----+      +-----+   |
         Real IP 1 ---------->*            *<---------- Real IP 2
                       |      |      *     |      |
                       +-------------^------------+
                              |      |     |
           -------------------+------|-----+-----+-------------+------
                                     |           ^             ^
                 Virtual IP --(VIPX)-+         (VIPX)        (VIPX)
                                                 |             |
                                              +--+--+       +--+--+
                                              |  H1 |       |  H2 |
                                              +-----+       +-----+

   The above configuration shows the most 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 utilization to be
   many environments where there is a distinct preference (or range of
   preferences) among the VRRP
   protocol. In set of redundant routers.  For example, this configuration, the hosts simply point their default
   routes at
   preference may be based upon access link cost or speed, router
   performance or reliability, or other policy considerations.  The
   protocol should allow the virtual IP address X (VIPX), expression of this relative path preference
   in an intuitive manner, and guarantee Master convergence to the routers run VRRP most
   preferential router currently available.

2.3 Minimization of Unnecessary Service Disruptions

   Once Master election has been performed then any unnecessary
   transitions between themselves. 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 on
   of equal or lower preference as long as the left is Master continues to
   function properly.

   Some environments may find it beneficial to avoid the default master state
   transition triggered when a router (MRX), and becomes available that is more
   preferential than the router on current Master.  It may be useful to support an
   override of the right is immediate convergence to the backup preferred path.

2.4 Extensible Security

   The virtual router (BRX).

      Legend:  ---+---+---+--  =  802 network, Ethernet or FDDI
                            H  =  Host computer
                           MR  =  Master Router
                           BR  =  Backup Router
                            *  =  IP Address
                          VIP  =  default gateway for hosts (Virtual IP)

4.2  Sample Configuration 2

   The following figure shows functionality is applicable to a more interesting VRRP network.

                  +--------------------------+
                  | Cluster X wide range of
   internetworking environments that may employ different security
   policies.  The protocol should require minimal configuration and Cluster Y  |
                  |                          |
                  |   +-----+      +-----+   |
                  |   | MRX |      | BRX |   |
                  |   |  &  |      |  &  |   |
                  |   | BRY |      | MRY |   |
                  |   +-----+      +-----+   |
    Real IP 1 ---------->*            *<---------- Real IP 2
                  |      |  *      *  |      |
                  +---------^------^---------+
                         |  |      |  |
       ------------------+--|------|--+-----+--------+--------+--------+--
                            |      |        ^        ^        ^        ^
        Virtual IP --(VIPX)-+      |      (VIPX)   (VIPY)   (VIPX)   (VIPY)
                                   |        |        |        |        |
        Virtual IP --(VIPY)--------+     +--+--+  +--+--+  +--+--+  +--+--+
                                         |  H1 |  |  H2 |  |  H3 |  |  H4 |
                                         +-----+  +-----+  +--+--+  +--+--+

   In
   overhead in the above configuration, half insecure operation, provide for strong authentication
   when increased security is required, and allow integration of new
   security mechanisms without breaking backwards compatible operation.

2.5 Efficient Operation over Extended LANs

   Sending IP packets on a multiaccess LAN requires mapping from the hosts point their default
   gateway at cluster X's
   virtual IP address (VIPX), and half to a MAC address.  The use of the hosts
   point their default gateway at cluster Y's virtual IP router
   MAC address (VIPY).
   This has the in an extended LAN employing learning bridges can have a
   significant effect of load balancing on the outgoing traffic, while
   also providing full redundancy.

      Legend:  ---+---+---+--  =  802 network, Ethernet or FDDI
                            H  =  Host computer
                           MR  =  Master Router
                           BR  =  Backup Router
                            *  =  IP Address
                          VIP  =  default gateway for hosts (Virtual IP)

5.  Protocol

   The purpose bandwidth overhead of the VRRP packet is to communicate packets sent to all other VRRP
   routers both the priority and
   virtual router.  If the state of virtual router MAC address is never used as
   the master's associated
   interface.

   VRRP packets are sent encapsulated in IP packets.  They are sent to
   an IPv4 multicast source address assigned for VRRP.

5.1  VRRP Packet Format

   This section defines in a link level frame then the format station location is
   never learned, resulting in flooding of all packets sent to the VRRP packet and
   virtual router.  To improve the relevant
   fields efficiency in this environment the IP 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    0 |    Version    | VRRP Cluster  |   Priority    |     Type      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    1 |   Auth Type   |   Adver Int   |          Checksum             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    2 |                      Virtual IP address                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    3 |                      Authentication Data                      |
      +---------------------------------------------------------------+
    4 |                                                               |
      +---------------------------------------------------------------+

5.2  IP Field Descriptions

5.2.1  Source Address

   The real IP address of
   protocol should: 1) use the interface virtual router MAC as the source in a
   packet is being sent from.

5.2.2  Destination Address

   The VRRP IP multicast address assigned by the IANA.  It is defined Master to
   be:

       224.0.0.(TBD IANA assignment)

   This is a link local scope multicast address.  Routers should not
   forward trigger station learning; 2) trigger a datagram with this destination address regardless of its
   TTL.

5.2.3  TTL

   The TTL should be set
   message immediately after transitioning to 255.  A VRRP router receiving a packet with
   the TTL not equal Master to 255 MUST discard update the packet.

5.2.4  Protocol

   The VRRP IP protocol number assigned by
   station learning; and 3) trigger periodic messages from the IANA.  It is defined Master to
   be (TBD).

5.3 VRRP Field Descriptions

5.3.1  Version

   The version field specifies
   maintain the station learning cache.

3.0 VRRP protocol version of this packet.
   This document defines version 1.

5.3.2 Overview

   VRRP Cluster assumes that each router has a consistent set of routes.  The VRRP Cluster field specifies
   mechanism used to learn or configure this routing state and ensure
   its consistency is beyond the cluster scope of this packet applies to.
   Note:  The interface may participate in more than one specification.

   VRRP cluster
   simultaneously, perhaps serving as master in one cluster, while
   simultaneously serving as backup in other clusters.

5.3.3  Priority

   The priority field specifies the currently configured VRRP priority
   value for this interface and cluster.  Higher values equal higher
   priority.  This field is an 8 bit unsigned field, giving 1 as the
   minimum priority, and 255 as election protocol to provide the maximum priority.  The default
   priority virtual router
   function described earlier.  All protocol messaging is 100 (decimal).

   Priority value performed
   using IP multicast datagrams, thus the protocol can operate over a
   variety of zero (0) multiaccess LAN technologies supporting IP multicast.
   Each VRRP virtual router has a special meaning.  It means that the
   current master had decided single well-known MAC address
   allocated to stop running VRRP. it.  This is used to
   cause other backup routers to quickly become master with out having
   to timeout document currently only details the current master.

   In mapping to
   networks using the event that two or more routers within a cluster have equal
   priority, and that priority IEEE 802 48-bit MAC address.  The virtual router
   MAC address is used as the highest priority source in all periodic messages sent by
   the cluster,
   initially the Master router to enable bridge learning in an extended LAN.

   A virtual router is identified by its virtual IP address, and
   associated with a VRRP cluster.  The virtual IP address must not
   match the higher real interface IP address
   (interpreted as a 32 bit unsigned integer) will become master.  Any
   new of any host or the virtual IP address of
   any other VRRP cluster on the LAN.  Each VRRP router joining assigned to the
   cluster must be configured with the same virtual IP address and must
   have a real IP address with a prefix matching the virtual router
   address. In addition, each VRRP router is assigned a priority to
   indicate the preference for Master election.  Multiple virtual
   routers can be elected on a network by associating them with
   different VRRP clusters, and a single router can participate in
   multiple VRRP clusters by maintaining independent state machines for
   each cluster.

   To minimize network traffic, only the Master router sends periodic
   Advertisement messages.  A Backup router will not become
   master even if attempt to pre-empt
   the Master unless it has a higher IP address priority.  This eliminates service
   disruption unless a more preferred path becomes available; it's also
   possible to administratively prohibit all pre-emption attempts.  If
   the current master
   goes down.

5.3.4  Type

   The type field specifies Master becomes unavailable then the type highest priority Backup will
   transition to Master after a short delay, providing a controlled
   transition of this the virtual router responsibility with minimal service
   interruption.

   VRRP packet.  The only
   packet type defines three types of authentication providing simple
   deployment in insecure environments, added protection against
   misconfiguration, and strong sender authentication in security
   conscious environments.  Analysis of the protection provided and
   vulnerability of each mechanism is deferred to Section 11.0 Security
   Considerations.  In addition new authentication types and data can be
   defined in this version the future without affecting the format of the fixed
   portion of the protocol is:

       1      ADVERTISEMENT

   All other values are currently unknown, packet, thus preserving backward compatible
   operation.

   The VRRP protocol design provides rapid transition from Backup to
   Master to minimize service interruption, and if a packet is received 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 value not listed, it should be discarded.

5.3.5  Authentication Type

   The authentication single
   message type field identifies the authentication method
   being utilized. and sender.  The current supported authentications typical operational scenarios are listed
   below:

      0 - No authentication
      1 - Simple text authentication
      2 - IP Security Option Authentication

   For simple text authentication any VRRP packet with an authentication
   string that does not match its configured authentication string
   should
   defined to be discarded.

   The authentication type field is an 8 bit number two redundant routers in a VRRP cluster (i.e., a Master
   and must be one of
   the above listed values.

5.3.5.1 IP Security Option Authentication

   When authentication Backup), 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 performed by using the IP Authentication
   Header as specified in [AUTH], the Authentication type should that duplicate
   packets may be set
   to "2".  If packet is received with forwarded for a brief period during Master election.
   However, the Authentication type set typical scenario assumptions are likely to
   "2" indicating IP security option authentication and no
   authentication header is present in cover the packet,
   vast majority of deployments, loss of the packet should be
   discarded.

5.3.6 Advertisement Interval (Adver Int)

   This field Master router is
   infrequent, and the time interval for expected duration in Master to Send ADVERTISEMENTS.
   Default election convergence
   is quite small ( << 1 second.  This field is used for troubleshooting
   misconfigured routers.

5.3.7 Checksum

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

   The checksum is the 16-bit one's complement of optimizations
   represent significant simplifications in the one's complement
   sum protocol design while
   incurring an insignificant probability of the entire brief network degradation.

4.  Sample Configurations

4.1  Sample Configuration 1

   The following figure shows a simple VRRP message starting with the version field.  For
   computing the checksum, the checksum field is set to zero.

5.3.8  Virtual network.

                       +--------------------------+
                       |        Cluster X         |
                       |                          |
                       |  +-------+    +-------+  |
                       |  |  MRX  |    |  BRX  |  |
                       |  |       |    |       |  |
                       |  |(P=200)|    |(P=100)|  |
                       |  |       |    |       |  |
                       |  +-------+    +-------+  |
         Real IP address

   The virtual 1 ---------->*            *<---------- Real IP address field specifies the 2
                       |      |      *     |      |
                       +-------------^------------+
                              |      |     |
           -------------------+------|-----+-----+-------------+------
                                     |           ^             ^
                 Virtual IP (VIP) address
   associated with the particular cluster.  This field is used --(VIPX)-+         (VIPX)        (VIPX)
                                                 |             |
                                              +--+--+       +--+--+
                                              |  H1 |       |  H2 |
                                              +-----+       +-----+

      Legend:
               ---+---+---+--  =  802 network, Ethernet or FDDI
                            H  =  Host computer
                           MR  =  Master Router (Priority=200)
                           BR  =  Backup Router (Priority=100)
                            *  =  IP Address
                          VIP  =  default router for
   troubleshooting misconfigured routers. hosts (Virtual IP)

   The VIP should be an above configuration shows a typical VRRP scenario.  In this
   configuration, the end-hosts install a default route to the virtual
   IP address assigned from (VIPX), and the subnet that routers run VRRP to elect the
   interface is attached.

5.3.9  Authentication Data Master
   router.  The authentication string is currently utilized for simple text
   authentication, similar to router on the simple text authentication found in
   OSPF.  It is up to 8 characters of plain text.  If left (MRX) becomes the configured
   authentication string is shorter than 8 bytes, Master router
   because it has the remaining space
   MUST be zero-filled. Any VRRP packet with an authentication string
   that does not match its configured authentication string should be
   discarded. The authentication string is unique highest priority and the router on the right (BRX)
   becomes the backup router.

4.2  Sample Configuration 2

   The following figure shows a per cluster
   basis.

6.  Protocol State Machine

6.1 Parameters

    Cluster_ID configuration with two clusters.

                  +--------------------------+
                  | Cluster identifier.  Configured item.

    Priority                Priority value for this cluster.  Configured
                            item.  Default is 100 (decimal).

    Virtual_IP              Virtual IP Address for this cluster.
                            Configured item.

    Advertisement_Interval  Time interval for Master to Send
                            ADVERTISEMENTS.  Default is 1 second.

    Skew_Time               Calculated time to skew
                            Master_Down_Interval.  Defined to be:

                               ( (256 - Priority) / 256 )
    Master_Down_Interval    Time interval for Backup to declare Master
                            down.  Defined to be:

                               (3 X and Cluster Y  |
                  |                          |
                  |   +-----+      +-----+   |
                  |   | MRX |      | BRX |   |
                  |   |  &  |      |  &  |   |
                  |   | BRY |      | MRY |   |
                  |   +-----+      +-----+   |
    Real IP 1 ---------->*            *<---------- Real IP 2
                  |      |  *      * Advertisement_Interval) + Skew_time

                            seconds.

6.2 Timers

    Master_Down_Timer       Timer which fires when Master has not been
                            heard for Master_Down_Interval.

    Adver_Timer             Timer which fires when time to send next
                            ADVERTISEMENT based on
                            Advertisement_Interval.

6.3  State Transition Diagram

                          +---------------+  |               |<-------------+
               +--------->|  Initialize      |
                  +---------^------^---------+
                         |  |      |               |----------+  |
       ------------------+--|------|--+-----+--------+--------+--------+--
                            |          +---------------+      |        ^        ^        ^        ^
        Virtual IP --(VIPX)-+      |      (VIPX)   (VIPX)   (VIPY)   (VIPY)
                                   |        |        |        |                                     V        |
       +---------------+                       +---------------+
        Virtual IP --(VIPY)--------+     +--+--+  +--+--+  +--+--+  +--+--+
                                         |               |---------------------->|  H1 |  |    Master  H2 |  |    Backup  H3 |  |               |<----------------------|  H4 |
       +---------------+                       +---------------+

6.4  State Descriptions
                                         +-----+  +-----+  +--+--+  +--+--+

      Legend:
               ---+---+---+--  =  802 network, Ethernet or FDDI
                            H  =  Host computer
                           MR  =  Master Router
                           BR  =  Backup Router
                            *  =  IP Address
                          VIP  =  default router for hosts (Virtual IP)

   In the below state descriptions, above configuration, half of the state names will be identified
   as follows {state-name}, hosts install a default route
   to cluster X's virtual IP address (VIPX), and the packets will be identified by
   utilizing all upper case characters.

6.4.1   Initialize

   {Initialize} is the initial state an interface takes when VRRP is
   enabled or disabled.  The basic function other half of the state is to wait for
   hosts install a startup event.  When that is received it:

      - Set the Master_Down_Timer to Master_Down_Interval
      - Set state default route to {Backup} state.

6.4.2   Backup cluster Y's virtual IP address
   (VIPY).  This has the effect of load balancing the outgoing traffic,
   while also providing full redundancy.

5.0  Protocol

   The main purpose of {Backup} state is for an interface to wait for the current master to stop sending ADVERTISEMENT packets.

   While in this state, an interface should do the following:

      - Should not respond to ARP request for the interface VIP router
         address

      - Should discard packets with destination link layer MAC address
         equal VRRP packet is to virtual router MAC.

      - Should discard packets addressed communicate to all VRRP routers
   the interface VIP address.

      - If Master_Down_Timer fires, Send ADVERTISEMENT, set Adver_Timer
         to Advertisement_Interval, priority and set state to {Master} state

      - If ADVERTISEMENT received,

            If Priority of the received ADVERTISEMENT is Zero, then set
            Mater_Down_Timer to Skew_Time.

            If Priority of the received ADVERTISEMENT is greater than
            this interfaces Priority, then reset Master_Down_Timer.

            If Priority of the received ADVERTISEMENT is equal to this
            interfaces Priority, then reset Master_Down_Timer.

            If Priority state of the received ADVERTISEMENT is lower than this
            interfaces Priority, then discard ADVERTISEMENT.

6.4.3 Master

   In {Master} state an interface is functioning as the actual physical router for associated with the virtual router
   Virtual IP and MAC address.

   While

   VRRP packets are sent encapsulated in this state, an interface should do the following:

   - Accept and forward traffic for the virtual router MAC address.

   - Respond IP packets.  They are sent to ARP requests for the VIP
   an IPv4 multicast address with the virtual router
      MAC address.

   - Respond to packets addressed assigned to VRRP.

5.1  VRRP Packet Format

   This section defines the VIP address.

   - If Adver_Timer fires, send a ADVERTISEMENT and reset Adver_Timer.

   - If ADVERTISEMENT received,

         If Priority format of the received ADVERTISEMENT is higher than this
         interfaces Priority, then cancel Adver_Timer, Set
         Master_Down_Timer, VRRP packet and set state to {Backup}.

         If Priority of the received ADVERTISEMENT is equal to this
         interfaces Priority, then:

            If IP Address of sender of ADVERTISEMENT is higher than this
            interfaces IP Address, then cancel Adver_Timer, Set
            Master_Down_Timer, and set state to {Backup}.

            If IP Address of sender of ADVERTISEMENT is lower than this
            interfaces IP Address, discard ADVERTISEMENT.

         If Priority of relevant
   fields in the received ADVERTISEMENT is lower than this
         interfaces Priority, discard ADVERTISEMENT.

6.5  State Table

   +---------------+---------------+---------------+---------------+
   |Current State->| {Initialize}  |   {Backup}    |   {Master}    |
   |               |               |               |               |
   |    Event      |               |               |               |
   |      |        |               |               |               |
   |      V        |               |               |               |
   +---------------+---------------+---------------+---------------+
   |               | Set Master_   |               |               |
   | Startup       |  Down_Timer   |               |               |
   |               | State =       |               |               |
   |               |  Backup       |               |               |
   +---------------+---------------+---------------+---------------+
   |               |               | Cancel Master_| Cancel Adver_ |
   | Shutdown      | Ignore        |  Down_Timer   |  Timer        |
   |               | Event         | State =       | Send ADVER w/ |
   |               |               |  Initialize   |  Priority=0   |
   |               |               |               | State = Init. |
   +---------------+---------------+---------------+---------------+
   |               |               | Send          |               |
   | Master_Down_  |               |  ADVERTISEMENT|               |
   | Timer fires   |               | Set Adver_    |               |
   |               |               |  Timer        |               |
   |               |               | State = Master|               |
   +---------------+---------------+---------------+---------------+
   | Adver_Timer   |               | IP 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    0 | Send ADVER.    Version    | VRRP Cluster  | fires   Priority    |     Type      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    1 | Reset Adver_   Auth Type   |   Adver Int   |          Checksum             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    2 |                      Virtual IP address                       |  Timer
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    3 |
   +---------------+---------------+---------------+---------------+                     Authentication Data                       | Receive VRRP
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    4 |                                                               | Set Master_   | Send ADVER.   |
   | ADVERTISEMENT |               |  Down_Timer=  | Reset Adver_  |
   | with Priority |               | Skew_Timer    |  Timer        |
   | equal Zero    |               |               |               |
   +---------------+---------------+---------------+---------------+
   | Receive VRRP  |               |               | Cancel Adver_ |
   | ADVERTISEMENT |               | Reset         |  Timer        |
   | with Higher   |               | Master_Down_  | Set Master__  |
   | Priority      |               | Timer         |  Down_Timer   |
   |               |               |               | State = Backup|
   +---------------+---------------+---------------+---------------+
   | Receive VRRP  |               |               | Cancel Adver_ |
   | ADVERTISEMENT |               | Reset         |  Timer        |
   | with Equal    |               | Master_Down_  | Set Master__  |
   | Priority      |               | Timer         |  Down_Timer   |
   | and Higher
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5.2  IP |               |               | State = Backup|
   | Field Descriptions

5.2.1  Source Address       |               |               |               |
   +---------------+---------------+---------------+---------------+
   | Receive VRRP  |               |               |               |
   | ADVERTISEMENT |               | Reset         |  Discard      |
   | with Equal    |               | Master_Down   |  Packet       |
   | Priority      |               | Timer         |               |
   | and Lower

   The real IP  |               |               |               |
   | address of the interface the packet is being sent from.

5.2.2  Destination Address       |               |               |               |
   +---------------+---------------+---------------+---------------+
   | Receive

   The VRRP  |               |               |               |
   | ADVERTISEMENT |               | Discard       |  Discard      |
   | IP multicast address assigned by the IANA.  It is defined to
   be:

       224.0.0.(TBD IANA assignment)

   This is a link local scope multicast address.  Routers MUST NOT
   forward a datagram with Lower    |               | Packet        |  Packet       |
   | Priority      |               |               |               |
   +---------------+---------------+---------------+---------------+
   | Receive ARP   |               |               |  Send ARP     |
   | Request for   |               | Discard       |  Reply w/     |
   | VIP this destination address regardless of its
   TTL.

5.2.3  TTL

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

5.2.4  Protocol

   The VRRP IP protocol number assigned by the IANA.  It is defined to
   be (TBD).

5.3 VRRP Field Descriptions

5.3.1  Version

   The version field specifies the VRRP protocol version of this packet.
   This document defines version 1.

5.3.2  VRRP Cluster

   The VRRP Cluster field specifies the cluster this packet applies to.
   Note:  The interface may participate in more than one VRRP cluster
   simultaneously, perhaps serving as Master in one cluster, while
   simultaneously serving as backup in other clusters.

5.3.3  Priority

   The priority field specifies the router's priority for the Virtual IP
   address and cluster.  Higher values equal higher priority.  This
   field is an 8 bit unsigned field, giving 1 as the minimum priority,
   and 255 as the maximum priority.  The default priority is 100
   (decimal).

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

   In the event that two or more routers within a cluster have equal
   priority, and that priority is the highest priority for the cluster,
   initially the router with the higher real interface IP address
   (interpreted as a 32 bit unsigned integer) will become Master.  Any
   router joining the cluster with the same priority will not become
   Master even if it has a higher IP address unless the current Master
   goes down.

5.3.4  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.

5.3.5  Authentication Type

   The authentication type field identifies the authentication method
   being utilized.  The authentication type field is an 8 bit number.  A
   packet with unknown authentication type or that does not match the
   locally configured authentication method MUST be discarded.

   The authentication methods currently defined are:

      0 - No Authentication
      1 - Simple Text Password
      2 - IP Authentication Header

5.3.5.1 No Authentication

   The use of this authentication type means that VRRP protocol
   exchanges are not authenticated.  The contents of the Authentication
   Data field should be set to zero on transmission and ignored on
   reception.

5.3.5.2 Simple Text Password

   The use of this authentication type means that VRRP protocol
   exchanges are authenticated by a clear text password.  The contents
   of the Authentication Data field should be set to the locally
   configured password on transmission.  There is no default password.
   The receiver MUST check that the Authentication Data in the packet
   matches its configured authentication string.  Packets that do not
   match MUST be discarded.

5.3.5.3 IP Authentication Header

   The use of this authentication type means the VRRP protocol exchanges
   are authenticated using the mechanisms defined by the IP
   Authentication Header [AUTH] using HMAC: Keyed-Hashing for Message
   Authentication [HMAC].  Keys may be either configured manually or via
   a key distribution protocol.

   If a packet is received that does not pass the authentication check
   due to a missing authentication header or incorrect message digest,
   then the packet MUST be discarded.  The contents of the
   Authentication Data field should 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.  For
   computing the checksum, the checksum field is set to zero.

5.3.8  Virtual IP address

   The virtual IP address field specifies the Virtual IP (VIP) address
   associated with the particular cluster.  This field is used for
   troubleshooting misconfigured routers.

   The VIP MUST be an IP address assigned from the subnet that the
   interface is attached and does not match any hosts real IP or cluster
   VIP address.

5.3.9  Authentication Data

   The authentication string is currently only utilized for simple text
   authentication, similar to the simple text authentication found in
   the Open Shortest Path First routing protocol [OSPF].  It is up to 8
   characters of plain text.  If the configured authentication string is
   shorter than 8 bytes, the remaining space MUST be zero-filled.  Any
   VRRP packet with an authentication string that does not match its
   configured authentication string SHOULD be discarded. The
   authentication string is unique on a per interface basis.

   There is no default value for this field.

6.  Protocol State Machine

6.1 Parameters

    Cluster_ID              Cluster identifier.  Configured item.  There
                            is no default.

    Priority                Priority value for this cluster.  Configured
                            item.  Range is between 1-255.  Default is
                            100 (decimal).

    Virtual_IP              Virtual IP Address for this cluster.
                            Configured item.

    Advertisement_Interval  Time interval between ADVERTISEMENTS in
                            seconds.  Default is 1 second.

    Skew_Time               Calculated time to skew Master_Down_Interval
                            in seconds. Defined to be:

                               ( (256 - Priority) / 256 )

    Master_Down_Interval    Time interval for Backup to declare Master
                            down in seconds.  Defined to be:

                               (3 * Advertisement_Interval) + Skew_time

    Preempt_Mode            Configuration switch controlling whether a
                            higher priority VRRP router preempts a lower
                            priority VRRP Master.  Values are True to
                            preempt and False to not preempt.  Default
                            is True.

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   |              | Packet        |  VMAC         |
   +---------------+---------------+---------------+---------------+
   | Receive IP    |               |               |  Process as   |
   | packet w/     |               |               |  Normal IP    |
   | Destination
               |          |               |----------+   |
               |          +---------------+          |   |
               |                                     |   |
               |                                     V   |
       +---------------+                       +---------------+
       |               |---------------------->|               |
       |    Master     |                       |    Backup     |  Packet sent
       |               |<----------------------|               |
       +---------------+                       +---------------+

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.

6.4.1   Initialize

   {Initialize} is the state a virtual router takes when VRRP is
   inactive.  The purpose of this state is to wait for a Startup event.
   If a Startup event is received, then:

      - Set the Master_Down_Timer to Master_Down_Interval

      - Transition to the {Backup} state

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, an virtual router MUST do the following:

    - MUST NOT respond to ARP requests for the virtual router IP address

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

    - MUST not accept packets addressed to the Virtual IP address
    - 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 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 physical
   router for the Virtual IP address.

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

    - MUST respond to ARP requests for the VIP address with the virtual
      router MAC address
    - Must accept and forward packets with a destination link layer MAC
      address equal to the virtual router MAC address

    - Must accept packets addressed to the VIP address

    - 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 IP Address of the sender is greater than
            the local IP 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

7.  Sending and Receiving VRRP Packets

7.1  Receiving VRRP Packets

   The following actions MUST be performed when a VRRP packet is
   received:

      - Verify that the IP TTL is 255.
      - Verify that the received packet length is greater than or equal
        to the VRRP header length
      - Verify the VRRP checksum
      - Verify the VRRP version
      - Perform authentication specified by Auth Type

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

      - Verify that the Cluster identifier and the VIP         |               |               | are valid on the
        receiving interface
      - Verify that the VIP in packet is same as the configured VIP for
        this cluster

   If any one of the above checks fails, the receiver MUST discard the
   packet.

      - 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 MAY indicate via network management that an
   error occurred.

7.2 Transmitting Packets

   The following operations MUST be performed prior to 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    |
   +---------------+---------------+---------------+---------------+
   | Receive IP    |               |               |  Process and  |
   | packet w/     |               |               |  Forward as   |
   | Dest. MAC     |               |               |  Normal IP    |
   | = VMAC        |               |               |  Packet       |
   +---------------+---------------+---------------+---------------+
   | Unknown Address
      - Send the VRRP  |               | Discard       |  Discard      |
   | packet        |               | Packet        |  Packet       |
   +---------------+---------------+---------------+---------------+

7.  Sending and Receiving to the VRRP Packets

7.1  Receiving IP multicast group

   Note: VRRP Packets packets are transmitted with the virtual 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 rules must format:

   00-00-5E-XX-XX-{cluster id} (in hex in internet standard bit-order)

   The first three octets are derived from the IANA's OUI.  The next two
   octets (to be performed when assigned by the IANA) indicate the address block
   assigned to the VRRP protocol.  {cluster id} is the VRRP cluster
   identifier.  This mapping provides for up to 255 VRRP clusters on a
   network.

8.  Host Operation

8.1  Host ARP Requests

   When a host sends an ARP request for the virtual IP address, the
   Master router MUST respond to the ARP request with the virtual MAC
   address for the virtual router.  This allows the client to always use
   the same MAC address regardless of the current Master router.  The
   request MUST be handled as a standard ARP reply.

9.  Operational Issues

9.1 ICMP Redirects

   VRRP packet operation relies on hosts only using the Virtual IP address.  It
   is received:

      - Verify TTL = 255.
      - Verify important that received packet length is greater or equal to VRRP
        header length.
      - Verify checksum in packet
      - Verify version
      - Verify Source address does client hosts do not equal interface learn the real IP address
      - Verify Cluster identifier valid of
   any VRRP router on received the LAN segment.  Consequently VRRP routers MUST
   NOT send ICMP Redirects on any interface
      - Perform indicated authentication
      - Verify VIP in packet they are running VRRP on.

9.2 Proxy ARP

   If Proxy ARP is same as configured VIP for this cluster
      - Verify Adver Interval to be used on a router running VRRP, then the VRRP
   router must advertise the Virtual Router MAC address in packet the Proxy ARP
   message.  Doing otherwise could cause hosts to learn the real IP
   address of the VRRP routers.

9.3 Network Management

   It is same important that network management tools (e.g., SNMP, Telnet,
   etc.) always use the real IP addresses of a VRRP router.  This
   ensures that network management is aware of the status of the real
   routers (e.g., to detect that a router has failed so that it can be
   repaired).

10.  Operation over FDDI and Token Ring

10.1 Operation over FDDI

   FDDI interfaces strip from the FDDI ring frames that have a source
   MAC address matching the device's hardware address.  Under some
   conditions, such as configured VIP for
        this cluster

   If router isolations, ring failures, protocol
   transitions, etc., VRRP may cause there to be more than one of these checks fails, Master
   router.  If a Master router installs the virtual router MAC address
   as the receiver should discard hardware address on a FDDI device, then other Masters'
   ADVERTISEMENTS will be stripped off the packet,
   log ring during the event Master
   convergence, and indicate via network management that convergence will fail.

   To avoid this an error
   occurred.

7.2 Transmitting Packets

   The following operations must be performed prior to transmitting implementations 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 stripping any ADVERTISEMENTS it did not originate.

10.2  Operation over Token Ring

   Token Ring has several characteristics which make running VRRP packet.
   problematic.  This includes:

    - Fill in packet fields No general multicast mechanism.  Required use of "functional
      addresses" as a substitute, which may collide with appropriate interface and cluster
        information
      - Compute Checksum other usage of
      the same "functional addresses".
    - Set source MAC Token Ring interfaces may have a limited ability to Virtual receive on
      multiple MAC Address addresses.
    - Send In order to VRRP IP Multicast Group

   Note: VRRP packets are transmitted with the Virtual MAC address as switch to a new master located on a different physical
      ring from the previous master when using source MAC route bridges, a
      mechanism is required to ensure that learning bridges correctly determine update cached source route information.

   Due the LAN segment these issues and the virtual MAC is attached to.

7.3 Virtual MAC Address

   The default virtual MAC address associated with limited knowledge about the virtual IP
   address is a IEEE 802 MAC Address detailed
   operation of Token Ring by the following format:

   00-00-5E-XX-XX-{cluster id} (in hex authors, this version of VRRP does not
   work over Token Ring networks.  This may be remedied in internet standard bit-order) new version
   of this document, or in a separate document.

11. Security Considerations

   VRRP is designed for a range of internetworking environments that may
   employ different security policies.  The first three octets are the IANA's OUI. protocol includes several
   authentication methods ranging from no authentication, simple clear
   text passwords, and strong authentication using IP Authentication
   with HMAC.  The next two octets (to
   be assigned by the IANA) indicate the address address block assigned details on each approach including possible attacks
   and recommended environments follows.

   Independent of any authentication type 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 the local attacks.

11.1 No Authentication

   The use of this authentication type means that VRRP protocol.  {cluster id} protocol
   exchanges are not authenticated.  This type of authentication SHOULD
   only be used in the last octet environments were there is the minimal security risk and
   little chance for configuration errors (e.g., two VRRP routers in a
   single cluster identifier.  This mapping allows for up to 255 on a link).

11.2 Simple Text Password

   The use of this authentication type means that VRRP clusters
   per interface.

   Implementations may also allow Virtual MAC addresses protocol
   exchanges are authenticated by a simple clear text password.

   This type of authentication is useful to be configured
   for each cluster.

8.  Host Operation

8.1  Host ARP Requests

   When protect against accidental
   misconfiguration of routers on a client sends link.  It protects against routers
   inadvertently becoming a ARP request for the virtual IP address, the
   appropriate master member of a VRRP cluster.  A new router should respond to the ARP request must
   first be configured with the
   above virtual MAC address for correct password before it can become a
   member of the appropriate VRRP cluster.  This allows
   the client to always use the same MAC address regardless type of authentication does not
   protect against hostile attacks where the
   current master router.  The request should password can be handled as learned by
   a standard
   ARP reply.

9.  Operational Issues

9.1 ICMP Redirects

   VRRP operation relies on the client host only using the Virtual IP
   address and corresponding Virutal MAC.  It is important that client
   hosts do not learn the real IP address of node snooping VRRP routers on LAN
   segment.  Consequentially routers packets on the same LAN segment MUST NOT
   send ICMP Redirects link.  The Simple Text
   Authentication combined with the real IP address of any TTL check makes it difficult for a
   VRRP routers.

9.2 Proxy ARP

   If Proxy ARP packet to be sent from another link to disrupt VRRP operation.

   This type of authentication is being used RECOMMENDED when there is minimal risk
   of nodes on routers running VRRP, the link actively disrupting VRRP routers
   must advertise the Virtual MAC address in the Proxy ARP message.
   Doing otherwise would cause them to learn the real operation.

11.3 IP address Authentication Header

   The use of this authentication type means the VRRP routers.

9.3 Network Management

   It is important that network management tools (e.g., SNMP, Telnet,
   etc.)  always use protocol exchanges
   are authenticated using the mechanisms defined by the real IP addresses of VRRP routers.
   Authentication Header [AUTH] using HMAC: Keyed-Hashing for Message
   Authentication [HMAC].  This provides strong protection against
   configuration errors, replay attacks, and packet
   corruption/modification.

   This type of authentication is
   necessary to insure that network management RECOMMENDED when there is aware limited
   control over the administration of nodes on the real
   status link.  While this
   type of authentication does protect the VRRP routers (e.g., detect that a router has failed so operation of VRRP, there are
   other types of attacks that it can may be repaired).

10.  Operation over Token Ring

   TBD

11. employed on shared media links
   (e.g., generation of bogus ARP replies) which are independent from
   VRRP and are not protected.

12.  References

   [AUTH]    Atkinson, R., "IP Authentication Header", RFC 1826, Naval
             Research Laboratory, RFC-1826, August
             1995.

   [DISC]    Deering, S., "ICMP Router Discovery Messages", RFC-1256,
             September 1991.

   [DHCP]    Droms, R., "Dynamic Host Configuration Protocol", RFC-1541,
             October 1993.

   [HMAC]    Krawczyk, H., M. Bellare, R. Canetti, "HMAC: Keyed-Hashing
             for Message Authentication", RFC-2104, February 1997.

   [HSRP]    Li, T., B. Cole, P. Morton, D. Li, "Hot Standby Router
             Protocol (HSRP)", Internet Draft, <draft-li-hsrp-00.txt>,
             June 1997.

   [OSPF]    Moy, J., "OSPF version 2", RFC-1583, July 1997.

   [RIP]     Hedrick, C., "Routing Information Protocol" , RFC-1058,
             June 1988.

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", RFC2119, RFC-2119, BCP14, March 1997.

12. Security Considerations

   The protocol design supports no authentication, simple text
   authentication, and integrity/authentication/integrity using the IP
   Security options.

13. Author's Addresses

   Steven Knight                           Phone: +1 612 943-8990
   Ascend Communications                   EMail: Steven.Knight@ascend.com
   High Performance Network Division
   10250 Valley View Road, Suite 113
   Eden Prairie, MN USA 55344
   USA

   Douglas Weaver                          Phone: +1 612 943-8990
   Ascend Communications                   EMail: Doug.Weaver@ascend.com
   High Performance Network Division
   10250 Valley View Road, Suite 113
   Eden Prairie, MN USA 55344
   USA
   David Whipple                           Phone: +1 206 703-3876
   Microsoft Corporation                   EMail: dwhipple@microsoft.com
   One Microsoft Way
   Redmond, WA USA 98052-6399
   USA

   Robert Hinden                           Phone: +1 408 990-2004
   Ipsilon Networks, Inc.                  EMail: hinden@ipsilon.com
   232 Java Drive
   Sunnyvale, CA 94089
   USA

   Danny Mitzel                            Phone: +1 408 990-2037
   Ipsilon Networks, Inc.                  EMail: mitzel@ipsilon.com
   232 Java Drive
   Sunnyvale, CA 94089
   USA

14. Acknowledgments

   The authors would like to thank Glen Zorn, and Michael Lane, Clark
   Bremer, Hal Peterson, Danny Mitzel, and Peter Hunt Hunt, Tony Li, Barbara Denny, and Steve
   Bellovin for their comments and suggestions.

15. Changes from Previous Drafts

   Changes from <draft-ietf-vrrp-spec-00.txt>

    - Added Preempt_Mode to allow user control over preemption
      independent of configured priorities.
    - Rewrote authentication section and expanded security
      considerations.
    - Expanded State Description section and removed State Table which
      become redundant and impossible to edit.
    - Changed authentication to be on a per interface basis (not per
      cluster).
    - Clarified text on disabling ICMP Redirects.
    - Added text on FDDI and Token Ring issues.
    - Added HSRP acknowledgment.
    - Rewrote Introduction, Required Features, and VRRP Overview
      sections.
    - Many small text clarifications.

   Changes from <draft-hinden-vrrp-00.txt>

    - Changed default behavior to stay with current master when
      priorities are equal.  This behavior can be changed by configuring
      explicit priorities.
    - Changed Master state behavior to not send Advertisements when
      receiving Advertisement with lower priorty. priority.  Change reduces worst
      case election message overhead to "n", where "n" is number of
      configured equal priority VRRP routers.
    - Added Skew_Time parameter and changed receiving advertisement with
      zero priority behavior to cause resulting advertisement sent to be
      skewed by priority.
    - Changed sending behavior to send VRRP packets with VMAC as source
      MAC and added text describing why this is important for bridged
      environments.
    - Changed definition of VMAC to be in IANA assigned unicast MAC
      block.
    - Added Advertisement Interval to VRRP header.
    - Added text regarding ICMP Redirects, Proxy ARP, and network
      management issues.
    - Various small text clarifications.