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INTERNET-DRAFT                                                  R. Hott
March 6, 2006                                                   NSWC-DD

          Timer Enhancements to Reduce Failover Times for the
              Virtual Router Redundancy Protocol for IPv4

                  <draft-ietf-vrrp-ipv4-timers-02.txt>


Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on September 6, 2006.


Abstract

   The router survivability capability provided by the Virtual
   Router Redundancy Protocol for IPv4 (VRRPv4) satisfies the
   requirements for many LAN environments. There are, however,
   LAN environments that have sub-second failover requirements and
   thus a need for finer granularity of the VRRP timers. This draft
   proposes extensions to VRRPv4 [RFC 3768] for specifying sub-second
   Advertisement Intervals. A new message type is introduced which
   permits the timer granularity for the Advertisement Interval to
   be specified. In addition, a new field is introduced permitting
   the specification of the number of missed ADVERTISEMENTs before
   a Virtual Router Master is declared down.




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Table of Contents

   1.  Introduction...............................................3
       1.1.  Requirements notation................................3
       1.2.  Contributors.........................................3
       1.3.  Scope................................................4
   2.  Update to the VRRPv4 Protocol..............................4
       2.1.  Updates to the VRRPv4 Packet Format..................4
       2.2.  Updates to the VRRPv4 Field Descriptions.............5
   3.  Update to the VRRPv4 Protocol State Machine................6
       3.1.  Updates to the Parementers per Virtual Router........6
       3.2.  Update to the Timers.................................8
       3.3.  Updates to the State Descriptions....................8
   4.  Updates for Sending and Receiving VRRPv4 Packets..........15
       4.1.  Receiving VRRPv4 Packets............................15
       4.2.  Transmitting VRRPv4 Packets.........................16
   5.  Operational Issues........................................17
       5.1.  Sub-second Timers...................................17
       5.2.  Interoperability / Backward Compatibility...........17
   6.  Security Considerations...................................17
   7.  Intellectual Property.....................................17
   8.  Acknowledgments...........................................18
   9.  IANA Considerations.......................................18
   10. Normative References......................................18
   11. Informative References....................................18
   12. Authors' Address..........................................19
   13. Disclaimer of Validity....................................19
   14. Copyright Statement.......................................19























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1.  Introduction

   VRRPv4 [RFC 3768] specifies an election protocol that dynamically
   assigns responsibility for a virtual router to one of the VRRP
   routers on a LAN. This election process provides dynamic fail
   over in the forwarding responsibility should the Master become
   unavailable. While this capability may meet the survivability
   requirements for many LAN environments, there are environments
   in which sub-second recovery from outages is required.

   To achieve sub-second failovers for VRRPv4, the granularity of
   the timers within VRRPv4 must be reduced from one second
   intervals to sub-second intervals. This document proposes an
   optional message type which permits the specification of the
   timer granularity. By specifying finer granularity timers, the
   Advertisement Interval can be specified, in increments, based
   upon the timer granularity.

   In addition to specifying the timer granularity and the
   Advertisement Interval in these new time increments, this
   document also proposes the ability to specify the number of
   ADVERTISEMENTS that must be missed prior to declaring a MASTER
   inactive. In the current specification for VRRPv4 [RFC 3768],
   the number of ADVERTISEMENTS missed prior to delaring a MASTER
   inactive is three, based upon the calculation of the
   Master_Down_Interval. In permitting the sub-second Advertisement
   Interval, the potential for VRRP instability is increased.
   Instability could occur due to processing requirements within the
   router preventing the processing of ADVERTISEMENTS or loading
   conditions on the network preventing reception of these
   ADVERTISEMENTS. Specifiying the number of ADVERTISEMENTS that
   can be missed offers a mechanism to address stability issues
   with VRRPv4, regardless of the timer granularity specified.

1.1.  Requirements notation

   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].

1.2.  Contributors

   The following people contributed to the text in this document: K.
   O'Donoghue, R. Hinden, S. Bates, S. Mathur, and M. Gupta. In
   addition, the authors of VRRPv4 [RFC 3768] are recognized as the
   basis for the text and concepts within this document.





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1.3.  Scope

   The remainder of this document provides a description of the
   optional message type for VRRPv4 and the associated changes to
   VRRPv4 to support this new message type and the added funtionality.

   A separate document will be produced if it is decided that similar
   functionality is desirable in the IPv6 environment.

2.  Update to the VRRPv4 Protocol

   This section outlines the changes to Section 5 (Protocol) of the
   VRRPv4 [RFC 3768] to accommodate the optional FAST ADVERTISEMENT,
   Type 2, message. Changes were made to the VRRPv4 packet format
   and VRRPv4 field descriptions. There were no changes made to
   the IP field descriptions.

2.1.  Updates to the VRRPv4 Packet Format

   This section outlines the VRRPv4 packet format for the optional
   Fast Advertisement, Type 2, message and the relevant fields in
   packet.

   The following is the VRRPv4 packet format for the mandatory
   ADVERTISEMENT, Type 1, message.

    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    | Count IP Addrs|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Auth Type   |   Adver Int   |          Checksum             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         IP Address (1)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            .                                  |
   |                            .                                  |
   |                            .                                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         IP Address (n)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Authentication Data (1)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Authentication Data (2)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+






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   The VRRPv4 packet format for the optional FAST ADVERTISEMENT,
   Type 2, message is as follows:

    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    | Count IP Addrs|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Adv Cnt|AIG|     Adver Int     |          Checksum             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         IP Address (1)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            .                                  |
   |                            .                                  |
   |                            .                                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         IP Address (n)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


2.2.  Updates to the VRRPv4 Field Descriptions

   The following updates the VRRPv4 field descriptions. The Type and
   Advertisement Interval are updated and two new fields are added.

2.2.1.  Type

   The Type field specifies the type of this VRRPv4 packet. There are
   two types defined

      1      ADVERTISEMENT
      2      FAST ADVERTISEMENT (optional)

   A packet with an unknown type MUST be discarded.

2.2.2.  Advertisement Count (Adv_Cnt)

   This field is only present in the FAST ADVERTISEMENT, Type 2,
   message. The Advertisement Count field specifies the number of FAST
   ADVERTISEMENT messages that can be missed before a BACKUP will
   declare a MASTER down. Configurable item in the range 1-15. Default
   is 3.








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2.2.3.  Advertisement Interval Granularity (AIG)

   This field is only present in the FAST ADVERTISEMENT, Type 2,
   message. The Advertisement Interval Granularity field specifies the
   timer granularity. The currently recognized values are

      0      seconds (default)
      1      centiseconds
      2      milliseconds

   A packet with an unknown Advertisement Interval Granularity MUST
   be discarded.

2.2.4.  Advertisement Interval (Adver Int)

   The Advertisement Interval field is present in both the
   ADVERTISEMENT and the FAST ADVERTISEMENT messages. The field
   indicates the number of time intervals between the respective
   advertisements. For the ADVERTISEMENT, Type 1, message the
   interval is measured in seconds and is an 8 bit field. For the
   FAST ADVERTISEMENT, Type 2, message the interval is measured in
   the units specified in the AIG field and is a 10 bit field. The
   default for the Advertisement Interval is 1 second.

3.  Update to the VRRPv4 Protocol State Machine

   This section outlines the changes to Section 6 (Protocol State
   Machine) of the VRRPv4 [RFC 3768] to accommodate the optional
   FAST ADVERTISEMENT, Type 2, message.

   With the introduction of the optional FAST ADVERTISEMENT message,
   time values MUST reflect the granularity supported in the FAST
   ADVERTISEMENT message. Thus all time values for both the
   ADVERTISEMENT and FAST ADVERTISEMENT message are specified
   according to the message format but are reflected internally
   in milliseconds.

   The state machines have also been updated to deal with
   interoperability issues due to addition of the new message type.

3.1.  Updates to the Parameters per Virtual Router

   VR_Type                 The message type for this VRRP router
                           Configurable item with values 1 for
                           ADVERTISEMENT and 2 for FAST
                           ADVERTISEMENT.




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   VR_Mode                 The mode of operation for this VRRP
                           router environment. Values are 0 for
                           a homogeneous VRRP router environment
                           and 1 for a heterogeneous VRRP router
                           environment (i.e., both message types
                           are used). The default is 0.

   VR_AIG                  The Advertisement Interval Granularity
                           for this VRRP router. Configurable item
                           with values 0 for seconds (default),
                           1 for centiseconds, and 2 for
                           milliseconds.

   VR_Adver_Interval       Time interval between ADVERTISEMENTs
                           or FAST ADVERTISEMENTs (milliseconds).
                           Configurable item. Default is 1,000
                           milliseconds (1 second) for both
                           message types.

   Advertisement_Interval  Time interval between ADVERTISEMENTs
                           or FAST ADVERTISEMENTs (milliseconds).

   Type1_Adver_Interval    Time interval between ADVERTISEMENTs
                           (seconds).

   Skew_Time               Time to skew Master_Down_Interval in
                           milliseconds. Calculated as:

                             ( ( ( 256 - Priority ) *
                             Advertisement_Interval ) / 256 ).

   VR_Adver_Count          The number of ADVERTISEMENTS or FAST
                           ADVERTISEMENTS that can be missed
                           before a BACKUP will declare a MASTER
                           down. Configurable item. When
                           ADVERTISEMENTs are used this is set to
                           3. When FAST ADVERTISEMENTs are used,
                           the range is 1-15. The default is 3.

   Advertisement_Count     The number of ADVERTISEMENTS or FAST
                           ADVERTISEMENTs that can be missed before
                           a BACKUP will declare a MASTER down.

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

                             ( Advertisement_Count *
                             Advertisement_Interval ) + Skew_time


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3.2.  Updates to the Timers

   With the introduction of the optional FAST ADVERTISEMENT message,
   time values MUST reflect the granularity supported in the FAST
   ADVERTISEMENT message. Thus all timers MUST reflect the granularity
   for FAST ADVERTISEMENT messages (milliseconds).

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

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

   Adver_2_Timer           Timer that fires to trigger sending of
                           FAST ADVERTISEMENT based on
                           Advertisement_Interval.

3.3.  Updates to the State Descriptions

   The State Transition Diagram does not change with the addition of
   the FAST ADVERTISMENT message type. The following updates the
   descriptions for the three states.

   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.

3.3.1.  Initialize

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

      o  Initialize local Virtual Router settings (VR_Mode, VR_Type,
         VR_AIG, VR_Adver_Interval, and VR_Adver_Count)

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

       If the VR_Type is 1, then:

        o  Send an ADVERTISEMENT
        o  Set the Adver_Timer to Advertisement_Interval



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       else:

        o  Send a FAST ADVERTISEMENT
        o  Set the Adver_2_Timer to Advertisement_Interval

       endif

       o  Broadcast a gratuitous ARP request containing the virtual
          router MAC address for each IP address associated with the
          virtual router.

       o  Transition to the {Master} state

      else:

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

      endif

3.3.2.  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:

       If the VR_Mode is 0, then:

        If the VR_Type is 1, then:



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         o  Send an ADVERTISEMENT
         o  Set the Adver_Timer to Advertisement_Interval

        else:

         o  Send a FAST ADVERTISEMENT
         o  Set the Adver_2_Timer to Advertisement_Interval

        endif

       else:

        o  Send an ADVERTISEMENT
        o  Send a FAST ADVERTISEMENT
        o  Set the Adver_Timer to Maximum of (1 second,
           Advertisement_Interval)
        o  Set the Adver_2_Timer to Advertisement_Interval

       endif

       o  Broadcast a gratuitous ARP request containing the virtual
          router MAC address for each IP address associated with the
          virtual router
       o  Transition to the {Master} state

      endif

   -  If an ADVERTISEMENT is received, then:

       If VR_Type is 2, then:

        o  Set the VR_Mode to 1 (mixed message type VRRP
           environment)

       endif

       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




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        else:

         o Discard the ADVERTISEMENT

        endif
       endif
      endif

   -  If a FAST ADVERTISEMENT is received, then:

       If VR_Type is 1, then:

        o  Set the VR_Mode to 1 (mixed message type VRRP
           environment)

       endif

       If the Priority in the FAST 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
        FAST 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 FAST ADVERTISEMENT

        endif
       endif
      endif

3.3.3.  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.

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   -  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  Cancel the Adver_2_Timer

       If the VR_Mode is 0, then

        If the VR_Type is 1, then:

         o  Send an ADVERTISEMENT with Priority = 0

        else

         o  Send a FAST ADVERTISEMENT with Priority = 0

        endif

       else

        o  Send an ADVERTISEMENT with Priority = 0
        o  Send a FAST ADVERTISEMENT with Priority = 0

       endif

   -  If the Adver_Timer fires, then:

       If the VR_Mode is 1
       or
       if the VR_Type is 1, then:

        o  Send an ADVERTISEMENT
        o  Reset the Adver_Timer to Maximum of (1 second,
           VR_Adver_Interval)

       endif
      endif

   -  If the Adver_2_Timer fires, then:

       If the VR_Mode is 1
       or
       if the VR_Type is 2, then:



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        o  Send a FAST ADVERTISEMENT
        o  Reset the Adver_2_Timer to VR_Adver_Interval

       endif
      endif

   -  If an ADVERTISEMENT is received, then:

       If the VR_Mode is 0
       and
       If the VR_Type is 2, then

        o  Set VR_Mode to 1 (heterogeneous VRRP environment)
        o  Set the Adver_Timer to Maximum of 1 second and
           VR_Adver_Interval

       endif

       If the Priority in the ADVERTISEMENT is Zero, then:

        If the VR_Mode is 0, then

         If the VR_Type is 1, then:

          o  Send an ADVERTISEMENT
          o  Reset the Adver_Timer to Maximum of 1 second and
             VR_Adver_Interval

         else

          o  Send a FAST ADVERTISEMENT
          o  Reset the Adver_2_Timer to VR_Adver_Interval

         endif

        else

         o  Send an ADVERTISEMENT
         o  Send a FAST ADVERTISEMENT
         o  Reset the Adver_Timer to Maximum of 1 second and
            VR_Adver_Interval
         o  Reset the Adver_2_Timer to VR_Adver_Interval

        endif

       else:





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        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  Cancel Adver_2_Timer
         o  Set Master_Down_Timer to Master_Down_Interval
         o  Transition to the {Backup} state

        else:

         o  Discard ADVERTISEMENT

        endif
       endif
      endif

   -  If a FAST ADVERTISEMENT is received, then:

       If the VR_Mode is 0
       and
       If the VR_Type is 1, then

        o  Set VR_Mode to 1 (heterogeneous VRRP environment)
        o  Set the Adver_2_Timer to VR_Adver_Interval

       endif

       If the Priority in the FAST ADVERTISEMENT is Zero, then:

        If the VR_Mode is 0, then

         o  Send a FAST ADVERTISEMENT
         o  Reset the Adver_2_Timer to VR_Adver_Interval

        else

         o  Send an ADVERTISEMENT
         o  Send a FAST ADVERTISEMENT
         o  Reset the Adver_Timer to Maximum of 1 second and
            VR_Adver_Interval
         o  Reset the Adver_2_Timer to VR_Adver_Interval

        endif

       else:


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        If the Priority in the FAST ADVERTISEMENT is greater
        than the local Priority,
        or
        If the Priority in the FAST 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  Cancel Adver_2_Timer
         o  Set Master_Down_Timer to Master_Down_Interval
         o  Transition to the {Backup} state

        else:

         o  Discard FAST ADVERTISEMENT

        endif
       endif
      endif

4.  Updates for Sending and Receiving VRRPv4 Packets

   This section outlines the changes to Section 7 (Sending and
   Receiving VRRP Packets) of the VRRPv4 [RFC 3768] to accommodate
   the optional FAST ADVERTISEMENT, Type 2, message.

4.1.  Receiving VRRPv4 Packets

   Perform 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
      packet (including fixed and variable fields) for either Type 1
      or Type 2 messages.
   -  MUST verify the VRRP checksum.
   -  MUST verify that the VRID is configured on the receiving
      interface and the local router is not the IP Address owner
      (Priority equals 255 (decimal)).
   -  For Type 1 (ADVERTISEMENT) messages, MUST verify that the
      Auth Type matches the locally configured authentication
      method for the virtual router and perform that
      authentication method.

   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.

   -  MAY verify that the message Type matches the locally
      configured VRRP Advertisement Type for the virtual router

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      (either Type 1 for ADVERTISEMENT or Type 2 for FAST
      ADVERTISEMENT).

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

   -  MAY verify that "Count IP Addrs" and the list of IP Address
      matches the IP_Addresses configured for the VRID.

   If the above check fails, the receiver SHOULD log the event
   and MAY 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.

   -  For Type 2 (FAST ADVERTISEMENT) messages, MUST verify that
      the Advertisement Count is the same as locally configured
      for this virtual router.
   -  For Type 2 (FAST ADVERTISEMENT) messages, MUST verify that
      the Advertisement Interval Granularity is the same as
      locally configured for this virtual router.
   -  MUST verify that the Advertisement Interval in the packet
      is the same as locally configured for this virtual router.

   If any of the above checks fail, the receiver SHOULD log the
   event and MAY indicate via network management that a
   misconfiguration was detected.

4.2.  Transmitting VRRPv4 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 (based on the message Type)
   -  Compute the VRRP checksum
   -  Set the source MAC address to Virtual Router MAC Address
   -  Set the source IP address to interface primary IP address
   -  Set the IP protocol to VRRP
   -  Send the VRRP packet to the VRRP IP multicast group

   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.





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5.  Operational Issues

5.1  Sub-second Timers

   The changes proposed to VRRP for IPv4 are intended to provide
   additional capabilities to address specific operational requirements,
   specifically, sub-second fail over from the Master. The use of
   sub-second timers is not recommended for general purpose networking
   environments. Missed ADVERTISEMENTS can lead to fail overs. Reducing
   the time period for fail over, the MASTER_DOWN_TIMER, increases the
   potential for missed ADVERTISEMENTS, due to router processing
   requirements, network congestion, or even denial of service attacks.

   The new message type provides extensions to VRRPv4 allowing the
   specification of sub-second timers. It also provides the ability to
   specify the number of advertisement messages that can be missed by
   a BACKUP before declaring a MASTER down.

5.2.  Interoperability / Backward Compatibility

   The addition of the new message type introduces the potential for
   routers that do not support the new message type configured on
   the same network with routers that use the new message type.
   The state machines have been updated to interoperate with routers
   only supporting Type 1 Advertisements. When routers configured to
   send Type 2 Fast Advertisements discover routers sending Type 1
   Advertisements, it sends both types of advertisements. In the
   Type 1 Advertisements, the Advertisement Interval is set to the
   larger of the interval value from the MASTER or one second (the
   minimum setting for Type 1 Advertisements). Type 2 messages will
   not support authentication.

6.  Security Considerations

   This draft does not address the security issues relating to VRRP
   that have been identified in RFC 3768.















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7.  Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed
   to pertain to the implementation or use of the technology described
   in this document or the extent to which any license under such
   rights might or might not be available; nor does it represent that
   it has made any independent effort to identify any such rights.
   Information on the procedures with respect to rights in RFC
   documents can be found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use
   of such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository
   at http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.


8.  Acknowledgments

   The work presented in this document is based upon the VRRP
   specification in RFC3768 and the current work in progress for VRRP
   for IPv6. The authors and contributors of these works are R.
   Hinden, P. Higginson, R. Hinden, P. Hunt, S. Knight, A. Lindem,
   D. Mitzel, M. Shand, D. Weaver, and D. Whipple.

   The author of this document would also like to thank Karen
   O'Donoghue, Leon Sangroniz, Changming Liu, Sonum Mathur,
   Mukesh Gupta, Steve Bates, and Bob Hinden for their
   guidance and helpful suggestions.


9.  IANA Considerations

   This document has no actions for IANA.









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10. Normative References

   [RFC3768] Hinden, R., Ed., "Virtual Router Redundancy Protocol
             (VRRP)", RFC 3768, April 2004.


11. Informative References

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

   [VRRP-IPv6]
             Hinden, R., "Virtual Router Redundancy Protocol for IPv6",
             draft-ietf-vrrp-ipv6-spec-07 (work in progress),
             September 2004.


12. Author's Address

   Robert W. Hott
   Naval Surface Warfare Center Dahlgren Division
   Code B35
   17320 Dahlgren Road
   Dahlgren, VA 22448-5100
   USA

   Phone: +1 540 653-1497
   EMail: robert.hott@navy.mil


13. Disclaimer of Validity

   This document and the information contained herein are provided on
   an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
   REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
   INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR
   IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

14. Copyright Statement

   Copyright (C) The Internet Society (2006).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.






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