draft-ietf-vrrp-spec-v2-05.txt

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5.3.6.3 IP Authentication Header

   The use of this authentication type means the VRRP protocol exchanges
   are authenticated using the mechanisms defined by the IP



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   Authentication Header [AUTH] using "The Use of HMAC-MD5-96 within ESP
   and AH" [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.

5.3.7 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.

5.3.8 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.  See
   RFC1071 for more detail [CKSM].

5.3.9  IP Address(es)

   One or more IP addresses that are associated with the virtual router.
   The number of addresses included is specified in the "Count IP Addrs"
   field.  These fields are used for troubleshooting misconfigured
   routers.

5.3.10  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 received with an authentication string that does not
   match the locally configured authentication string MUST be discarded.
   The authentication string is unique on a per interface basis.

   There is no default value for this field.






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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 IP
                            addresses 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).

    IP_Addresses            One or more IP addresses 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 IP address(es) associated with the
                            virtual router always pre-empts independent
                            of the setting of this flag.



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    Authentication_Type     Type of authentication being used.  Values
                            are defined in section 5.3.6.

    Authentication_Data     Authentication data specific to the
                            Authentication_Type being used.


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:




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

       o Send an ADVERTISEMENT
       o Broadcast a gratuitous ARP request containing the virtual
         router MAC address for each IP address associated with the
         virtual router.
       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 ARP requests for the IP address(s) associated
      with 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 IP address(es) 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 Broadcast a gratuitous ARP request containing the virtual
         router MAC address for each IP address associated with the
         virtual router
       o Set the Adver_Timer to Advertisement_Interval
       o Transition to the {Master} state



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      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 IP address(es) associated with the virtual router.

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

    - MUST respond to ARP requests for the IP address(es) associated
      with the virtual router.

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

    - MUST NOT accept packets addressed to the IP address(es) associated
      with the virtual router if it is not the IP address owner.

    - MUST accept packets addressed to the IP address(es) associated
      with the virtual router if it is the IP 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



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















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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 IP TTL is 255.
      - MUST verify the VRRP version is 2
      - MUST verify that the received packet contains the complete VRRP