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RFC 4286 - Multicast Router Discovery


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Network Working Group                                        B. Haberman
Request for Comments: 4286                                       JHU APL
Category: Standards Track                                      J. Martin
                                                             Netzwert AG
                                                           December 2005

                       Multicast Router Discovery

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   The concept of Internet Group Management Protocol (IGMP) and
   Multicast Listener Discovery (MLD) snooping requires the ability to
   identify the location of multicast routers.  Since snooping is not
   standardized, there are many mechanisms in use to identify the
   multicast routers.  However, this can lead to interoperability issues
   between multicast routers and snooping switches from different
   vendors.

   This document introduces a general mechanism that allows for the
   discovery of multicast routers.  This new mechanism, Multicast Router
   Discovery (MRD), introduces a standardized means of identifying
   multicast routers without a dependency on particular multicast
   routing protocols.

Table of Contents

   1. Introduction ....................................................3
   2. Protocol Overview ...............................................3
   3. Multicast Router Advertisement ..................................4
      3.1. Advertisement Configuration Variables ......................4
           3.1.1. AdvertisementInterval ...............................5
           3.1.2. AdvertisementJitter .................................5
           3.1.3. MaxInitialAdvertisementInterval .....................5
           3.1.4. MaxInitialAdvertisements ............................5
           3.1.5. NeighborDeadInterval ................................5
           3.1.6. MaxMessageRate ......................................6
      3.2. Advertisement Packet Format ................................6
           3.2.1. Type Field ..........................................6
           3.2.2. Advertisement Interval Field ........................6
           3.2.3. Checksum Field ......................................6
           3.2.4. Query Interval Field ................................7
           3.2.5. Robustness Variable Field ...........................7
      3.3. IP Header Fields ...........................................7
           3.3.1. Source Address ......................................7
           3.3.2. Destination Address .................................7
           3.3.3. Time-to-Live / Hop Limit ............................7
           3.3.4. IPv4 Protocol .......................................7
           3.3.5. IPv6 Next Header ....................................7
      3.4. Sending Multicast Router Advertisements ....................8
      3.5. Receiving Multicast Router Advertisements ..................8
   4. Multicast Router Solicitation ...................................9
      4.1. Solicitation Packet Format .................................9
           4.1.1. Type Field ..........................................9
           4.1.2. Reserved Field ......................................9
           4.1.3. Checksum Field ......................................9
      4.2. IP Header Fields ..........................................10
           4.2.1. Source Address .....................................10
           4.2.2. Destination Address ................................10
           4.2.3. Time-to-Live / Hop Limit ...........................10
           4.2.4. IPv4 Protocol ......................................10
           4.2.5. IPv6 Next Header ...................................10
      4.3. Sending Multicast Router Solicitations ....................10
      4.4. Receiving Multicast Router Solicitations ..................10
   5. Multicast Router Termination ...................................11
      5.1. Termination Packet Format .................................11
           5.1.1. Type Field .........................................11
           5.1.2. Reserved Field .....................................11
           5.1.3. Checksum Field .....................................11
      5.2. IP Header Fields ..........................................12
           5.2.1. Source Address .....................................12
           5.2.2. Destination Address ................................12
           5.2.3. Time-to-Live / Hop Limit ...........................12

           5.2.4. IPv4 Protocol ......................................12
           5.2.5. IPv6 Next Header ...................................12
      5.3. Sending Multicast Router Terminations .....................12
      5.4. Receiving Multicast Router Terminations ...................12
   6. Protocol Constants .............................................13
   7. Security Considerations ........................................13
   8. IANA Considerations ............................................14
   9. Acknowledgements ...............................................15
   10. References ....................................................15
      10.1. Normative References .....................................15
      10.2. Informative Reference ....................................16

1.  Introduction

   Multicast Router Discovery (MRD) messages are useful for determining
   which nodes attached to a switch have multicast routing enabled.
   This capability is useful in a layer-2 bridging domain with snooping
   switches.  By utilizing MRD messages, layer-2 switches can determine
   where to send multicast source data and group membership messages [1]
   [2].  Multicast source data and group membership reports must be
   received by all multicast routers on a segment.  Using the group
   membership protocol Query messages to discover multicast routers is
   insufficient due to query suppression.

   Although MRD messages could be sent as ICMP messages, the group
   management protocols were chosen since this functionality is
   multicast specific.  The addition of this functionality to the group
   membership protocol also allows operators to have congruence between
   MRD problems and data forwarding issues.

   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 [3].

2.  Protocol Overview

   Multicast Router Discovery consists of three messages for discovering
   multicast routers.  The Multicast Router Advertisement is sent by
   routers to advertise that IP multicast forwarding is enabled.
   Devices may send Multicast Router Solicitation messages in order to
   solicit Advertisement messages from multicast routers.  The Multicast
   Router Termination messages are sent when a router stops IP multicast
   routing functions on an interface.

   Multicast routers send unsolicited Advertisements periodically on all
   interfaces on which multicast forwarding is enabled.  Advertisement
   messages are also sent in response to Solicitations.  In addition to
   advertising the location of multicast routers, Advertisements also

   convey useful information concerning group management protocol
   variables.  This information can be used for consistency checking on
   the subnet.

   A device sends Solicitation messages whenever it wishes to discover
   multicast routers on a directly attached link.

   A router sends Termination messages when it terminates multicast
   routing functionality on an interface.

   All MRD messages are sent with an IPv4 Time to Live (TTL) or IPv6 Hop
   Limit of 1 and contain the Router Alert Option [4] [5].  All MRD
   messages SHOULD be rate-limited as per the MaxMessageRate variable.

   Advertisement and Termination messages are sent to the All-Snoopers
   multicast address.

   Solicitation messages are sent to the All-Routers multicast address.

   Any data beyond the fixed message format MUST be ignored.

3.  Multicast Router Advertisement

   Multicast Router Advertisements are sent unsolicited periodically on
   all router interfaces on which multicast forwarding is enabled.  They
   are also sent in response to Multicast Router Solicitation messages.

   Advertisements are sent

   1.  Upon the expiration of a periodic (modulo randomization) timer

   2.  As part of a router's start-up procedure

   3.  During the restart of a multicast forwarding interface

   4.  On receipt of a Solicitation message

   All Advertisements are sent as Internet Group Management Protocol
   (for IPv4) or Multicast Listener Discovery (for IPv6) messages to the
   All-Snoopers multicast address.  These messages SHOULD be rate-
   limited as per the MaxMessageRate variable.

3.1.  Advertisement Configuration Variables

   An MRD implementation MUST support the following variables being
   configured by system management.  Default values are specified to
   make it unnecessary to configure any of these variables in many
   cases.

3.1.1.  AdvertisementInterval

   This variable is the base interval (in integer seconds) between the
   transmissions of unsolicited Advertisements on an interface.  This
   value MUST be no less than 4 seconds and no greater than 180 seconds.

   Default: 20 seconds

3.1.2.  AdvertisementJitter

   This is the maximum time (in seconds) by which the
   AdvertisementInterval is perturbed for each unsolicited
   Advertisement.  Note that the purpose of this jitter is to avoid
   synchronization of multiple routers on a network, hence choosing a
   value of zero is discouraged.  This value MUST be an integer no less
   than 0 seconds and no greater than AdvertisementInterval.

   The AdvertisementJitter MUST be  0.025*AdvertisementInterval

3.1.3.  MaxInitialAdvertisementInterval

   The first unsolicited Advertisement transmitted on an interface is
   sent after waiting a random interval (in seconds) less than this
   variable.  This prevents a flood of Advertisements when multiple
   routers start up at the same time.

   Default: 2 seconds

3.1.4.  MaxInitialAdvertisements

   This variable is the maximum number of unsolicited Advertisements
   that will be transmitted by the advertising interface when MRD starts
   up.

   Default: 3

3.1.5.  NeighborDeadInterval

   The NeighborDeadInterval variable is the maximum time (in seconds)
   allowed to elapse (after receipt of the last valid Advertisement)
   before a neighboring router is declared unreachable.  This variable
   is maintained per neighbor.  An MRD receiver should set the
   NeighborDeadInterval to 3 times the sum of Advertisement Interval
   Field received plus the AdvertisementJitter calculated from the
   received Advertisement Interval Field.  This ensures consistent
   behavior between multiple devices on a network.

   Default : 3 * (Advertisement Interval Field + calculated
   AdvertisementJitter)

3.1.6.  MaxMessageRate

   The MaxMessageRate variable is the maximum aggregate number of
   messages an MRD implementation SHOULD send (per second) per interface
   or per management or logging destination.

   Default: 10

3.2.  Advertisement Packet Format

   The Advertisement message has the following format:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Type     |  Ad. Interval |            Checksum           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Query Interval        |      Robustness Variable      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.2.1.  Type Field

   The Type field identifies the message as an Advertisement.  It is set
   to 0x30 for IPv4 and 151 for IPv6.

3.2.2.  Advertisement Interval Field

   This field specifies the periodic time interval at which unsolicited
   Advertisement messages are transmitted in units of seconds.  This
   value is set to the configured AdvertisementInterval.

3.2.3.  Checksum Field

   The checksum field is set as follows:

   1.  For IPv4 it is the 16-bit one's complement of the one's
       complement sum of the IGMP message, starting with the Type field.
       For computing the checksum, the checksum field is set to 0.

   2.  For IPv6 it is ICMPv6 checksum as specified in [6].

3.2.4.  Query Interval Field

   The Query Interval field is set to the Query Interval value (in
   seconds) in use by IGMP or MLD on the interface.  If IGMP or MLD is
   not enabled on the advertising interface, this field MUST be set to
   0.  Note that this is the Querier's Query Interval (QQI), not the
   Querier's Query Interval Code (QQIC) as specified in the IGMP/MLD
   specifications.

3.2.5.  Robustness Variable Field

   This field is set to the Robustness Variable in use by IGMPv2 [2],
   IGMPv3 [7], or MLD [8] [9] on the advertising interface.  If IGMPv1
   is in use or no group management protocol is enabled on the
   interface, this field MUST be set to 0.

3.3.  IP Header Fields

3.3.1.  Source Address

   The IP source address is set to an IP address configured on the
   advertising interface.  For IPv6, a link-local address MUST be used.

3.3.2.  Destination Address

   The IP destination address is set to the All-Snoopers multicast
   address.

3.3.3.  Time-to-Live / Hop Limit

   The IPv4 TTL and IPv6 Hop Limit are set to 1.

3.3.4.  IPv4 Protocol

   The IPv4 Protocol field is set to IGMP (2).

3.3.5.  IPv6 Next Header

   The ICMPv6 header is identified by a Next Header value of 58 in the
   immediately preceding header [6].

3.4.  Sending Multicast Router Advertisements

   Advertisement messages are sent when the following events occur:

   1.  The expiration of the periodic advertisement interval timer.
       Note that this timer is not strictly periodic since the base
       AdvertisementInterval is varied at each interval by a random
       value no more than plus or minus AdvertisementJitter seconds.

   2.  After a random delay less than MaxInitialAdvertisementInterval
       when an interface is first enabled, is (re-)initialized, or MRD
       is enabled.  A router may send up to a maximum of
       MaxInitialAdvertisements Advertisements, waiting for a random
       delay less than MaxInitialAdvertisementInterval between each
       successive message.  Multiple Advertisements are sent for
       robustness in the face of packet loss on the network.

   This is to prevent an implosion of Advertisements.  An example of
   this occurring would be when many routers are powered on at the same
   time.  When a Solicitation is received, an Advertisement is sent in
   response with a random delay less than MAX_RESPONSE_DELAY.  If a
   Solicitation is received while an Advertisement is pending, that
   Solicitation MUST be ignored.

   Changes in the Query Interval or Robustness Variable MUST NOT trigger
   a new Advertisement; however, the new values MUST be used in all
   future Advertisement messages.

   When an Advertisement is sent, the periodic advertisement interval
   timer MUST be reset.

3.5.  Receiving Multicast Router Advertisements

   Upon receiving an Advertisement message, devices validate the message
   with the following criteria:

   1.  The checksum is correct

   2.  The IP destination address is equal to the All-Snoopers multicast
       address

   3.  For IPv6, the IP source address is a link-local address

   An Advertisement not meeting the validity requirements MUST be
   silently discarded and may be logged in a rate-limited manner as per
   the MaxMessageRate variable.

   If an Advertisement is not received for a particular neighbor within
   a NeighborDeadInterval time interval, then the neighbor is considered
   unreachable.

4.  Multicast Router Solicitation

   Multicast Router Solicitation messages are used to solicit
   Advertisements from multicast routers on a segment.  These messages
   are used when a device wishes to discover multicast routers.  Upon
   receiving a solicitation on an interface with IP multicast forwarding
   and MRD enabled, a router will respond with an Advertisement.

   Solicitations may be sent when these occur:

   1.  An interface is (re-)initialized

   2.  MRD is enabled

   Solicitations are sent to the All-Routers multicast address and
   SHOULD be rate-limited, as per the MaxMessageRate variable.

4.1.  Solicitation Packet Format

   The Solicitation message has the following format:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |   Reserved    |           Checksum            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.1.1.  Type Field

   The Type field identifies the message as a Solicitation.  It is set
   to 0x31 for IPv4 and 152 for IPv6.

4.1.2.  Reserved Field

   The Reserved field is set to 0 on transmission and ignored on
   reception.

4.1.3.  Checksum Field

   The checksum field is set as follows:

   o  For IPv4 it is the 16-bit one's complement of the one's complement
      sum of the IGMP message, starting with the Type field.  For
      computing the checksum, the checksum field is set to 0.

   o  For IPv6 it is ICMPv6 checksum as specified in [6].

4.2.  IP Header Fields

4.2.1.  Source Address

   The IP source address is set to an IP address configured on the
   soliciting interface.  For IPv6, a link-local address MUST be used.

4.2.2.  Destination Address

   The IP destination address is set to the All-Routers multicast
   address.

4.2.3.  Time-to-Live / Hop Limit

   The IPv4 TTL and IPv6 Hop Limit are set to 1.

4.2.4.  IPv4 Protocol

   The IPv4 Protocol field is set to IGMP (2).

4.2.5.  IPv6 Next Header

   The ICMPv6 header is identified by a Next Header value of 58 in the
   immediately preceding header [6].

4.3.  Sending Multicast Router Solicitations

   Solicitation messages are sent when the following events occur:

   o  After waiting for a random delay less than MAX_SOLICITATION_DELAY
      when an interface first becomes operational, is (re-)initialized,
      or MRD is enabled.  A device may send up to a maximum of
      MAX_SOLICITATIONS, waiting for a random delay less than
      MAX_SOLICITATION_DELAY between each solicitation.

   o  Optionally, for an implementation specific event.

   Solicitations MUST be rate-limited as per the MaxMessageRate
   variable; the implementation MUST send no more than MAX_SOLICITATIONS
   in MAX_SOLICITATION_DELAY seconds.

4.4.  Receiving Multicast Router Solicitations

   A Solicitation message MUST be validated before a response is sent.
   A router MUST verify the following:

   o  The checksum is correct.

   o  The IP destination address is the All-Routers multicast address.

   o  For IPv6, the IP source address MUST be a link-local address.

   Solicitations not meeting the validity requirements SHOULD be
   silently discarded and may be logged in a rate-limited manner as per
   the MaxMessageRate variable.

5.  Multicast Router Termination

   The Multicast Router Termination message is used to expedite the
   notification of a change in the status of a router's multicast
   forwarding functions.  Multicast routers send Terminations when
   multicast forwarding is disabled on the advertising interface.

5.1.  Termination Packet Format

   The Termination message has the following format:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |   Reserved    |            Checksum           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5.1.1.  Type Field

   The Type field identifies the message as a Termination.  It is set to
   0x32 for IPv4 and 153 for IPv6.

5.1.2.  Reserved Field

   The Reserved field is set to 0 on transmission and ignored on
   reception.

5.1.3.  Checksum Field

   The checksum field is set as follows:

   o  For IPv4 it is the 16-bit one's complement of the one's complement
      sum of the IGMP message, starting with the Type field.  For
      computing the checksum, the checksum field is set to 0.

   o  For IPv6 it is ICMPv6 checksum as specified in [6].

5.2.  IP Header Fields

5.2.1.  Source Address

   The IP source address is set to an IP address configured on the
   advertising interface.  For IPv6, a link-local address MUST be used.

5.2.2.  Destination Address

   The IP destination address is set to the All-Snoopers multicast
   address.

5.2.3.  Time-to-Live / Hop Limit

   The IPv4 TTL and IPv6 Hop Limit are set to 1.

5.2.4.  IPv4 Protocol

   The IPv4 Protocol field is set to IGMP (2).

5.2.5.  IPv6 Next Header

   The ICMPv6 header is identified by a Next Header value of 58 in the
   immediately preceding header [6].

5.3.  Sending Multicast Router Terminations

   Termination messages are sent by multicast routers when

   o  Multicast forwarding is disabled on an interface

   o  An interface is administratively disabled

   o  The router is gracefully shut down

   o  MRD is disabled

   The sending of Termination messages SHOULD be rate-limited as per the
   MaxMessageRate variable.

5.4.  Receiving Multicast Router Terminations

   Upon receiving a Termination message, devices validate the message.
   The validation criteria are the following:

   o  Checksum MUST be correct.

   o  IP destination address MUST equal the All-Snoopers multicast
      address.

   o  For IPv6, the IP source address MUST be a link-local address.

   Termination messages not meeting the validity requirements MUST be
   silently discarded and may be logged in a rate-limited manner as per
   the MaxMessageRate variable.

   If the message passes these validation steps, a Solicitation is sent.
   If an Advertisement is not received within NeighborDeadInterval, the
   sending router is removed from the list of active multicast routers.

6.  Protocol Constants

   The following list identifies constants used in the MRD protocol.
   These constants are used in the calculation of parameters.

   o  MAX_RESPONSE_DELAY 2 seconds

   o  MAX_SOLICITATION_DELAY 1 second

   o  MAX_SOLICITATIONS 3 transmissions

7.  Security Considerations

   As MRD is a link-local protocol, there is no circumstance in which it
   would be correct for an MRD receiver to receive MRD traffic from an
   off-network source.  For IPv6, MRD messages MUST have a valid link-
   local source address.  Any messages received without a valid link-
   local source address MUST be discarded.  Similarly, for IPv4, the MRD
   receiver MUST determine if the source address is local to the
   receiving interface, and MUST discard any messages that have a non-
   local source.  Determining what networks are local may be
   accomplished through configuration information or operational
   capabilities.

   Rogue nodes may attempt to attack a network running MRD by sending
   spoofed Advertisement, Solicitation, or Termination messages.  Each
   type of spoofed message can be dealt with using existing technology.

   A rogue node may attempt to interrupt multicast service by sending
   spoofed Termination messages.  As described in Section 5.4, all
   Termination messages are validated by sending a Solicitation message.
   By sending a Solicitation, the node will force the transmission of an
   Advertisement by an active router.

   Spoofed Solicitation messages do not cause any operational harm.
   They may be used as a flooding mechanism to attack a multicast
   router.  This attack can be mitigated through the rate-limiting
   recommendation for all MRD messages.

   The Multicast Router Advertisement message may allow rogue machines
   to masquerade as multicast routers.  This could allow those machines
   to eavesdrop on multicast data transmissions.  Additionally, it could
   constitute a denial of service attack to other hosts in the same
   snooping domain or sharing the same device port in the presence of
   high-rate multicast flows.

   The technology available in SEND [10] can be utilized to address
   spoofed Advertisement messages in IPv6 networks.  IPv6 Multicast
   routers in an MRD-enabled network can use SEND-based link-local
   addresses as the IPv6 source address for MRD messages.  When a switch
   receives an initial Advertisement, it can use the information in the
   SEND-based address to challenge the router to authenticate itself.
   It should be noted that this approach only applies to IPv6 networks.

   Another solution that supports both IPv4 and IPv6 is to use IPsec in
   Encapsulating Security Payload (ESP) mode [11] to protect against
   attacks by ensuring that messages came from a system with the proper
   key.  When using IPsec, the messages sent to the All-Snoopers address
   should be authenticated using ESP.  Should encryption not be desired,
   ESP with a null encryption algorithm and a symmetric authentication
   algorithm, such as HMAC-SHA-1, is viable.  For keying, a symmetric
   signature algorithm with a single manually configured key is used for
   routers sending Advertisements.  This allows validation that the MRD
   message was sent by a system with the key.  It should be noted that
   this does not prevent a system with the key from forging a message
   and it requires the disabling of IPsec's Replay Protection.  It is
   the responsibility of the network administrator to ensure that the
   same key is present on all possible MRD participants.

8.  IANA Considerations

   This document introduces three new IGMP messages.  Each of these
   messages requires a new IGMP Type value.  The IANA has assigned three
   new IGMP Type values to the Multicast Router Discovery Protocol:

    +-----------+-----------------+--------------------------------+
    | IGMP Type |     Section     |          Message Name          |
    +-----------+-----------------+--------------------------------+
    |   0x30    |  Section 3.2.1  | Multicast Router Advertisement |
    |   0x31    |  Section 4.1.1  | Multicast Router Solicitation  |
    |   0x32    |  Section 5.1.1  | Multicast Router Termination   |
    +-----------+-----------------+--------------------------------+

   This document also introduces three new MLD messages.  Each of these
   messages requires a new ICMPv6 Type value.  The IANA has assigned
   three new ICMPv6 Type values from the Informational range:

   +-------------+-----------------+--------------------------------+
   | ICMPv6 Type |     Section     |          Message Name          |
   +-------------+-----------------+--------------------------------+
   |     151     |  Section 3.2.1  | Multicast Router Advertisement |
   |     152     |  Section 4.1.1  | Multicast Router Solicitation  |
   |     153     |  Section 5.1.1  | Multicast Router Termination   |
   +-------------+-----------------+--------------------------------+

   This document also requires the assignment of an All-Snoopers
   multicast address for IPv4.  This multicast address is in the
   224.0.0/24 range since it is used for link-local, control messages.
   The IPv4 multicast address for All-Snoopers is 224.0.0.106.

   A corresponding IPv6 multicast address has also been assigned.
   Following the guidelines in [12], the IPv6 multicast address is a
   link-local in scope and has a group-ID value equal to the low-order 8
   bits of the requested IPv4 multicast address.  The IPv6 multicast
   address is FF02:0:0:0:0:0:0:6A.

9.  Acknowledgements

   Brad Cain and Shantam Biswis are the authors of the original
   Multicast Router Discovery proposal.

   ICMP Router Discovery [13] was used as a general model for Multicast
   Router Discovery.

   Morten Christensen, Pekka Savola, Hugh Holbrook, and Isidor Kouvelas
   provided helpful feedback on various versions of this document.

10.  References

10.1.  Normative References

   [1]   Deering, S., "Host extensions for IP multicasting", STD 5, RFC
         1112, August 1989.

   [2]   Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
         Thyagarajan, "Internet Group Management Protocol, Version 3",
         RFC 3376, October 2002.

   [3]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.

   [4]   Katz, D., "IP Router Alert Option", RFC 2113, February 1997.

   [5]   Partridge, C. and A. Jackson, "IPv6 Router Alert Option", RFC
         2711, October 1999.

   [6]   Conta, A. and S. Deering, "Internet Control Message Protocol
         (ICMPv6) for the Internet Protocol Version 6 (IPv6)
         Specification", RFC 2463, December 1998.

   [7]   Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
         Thyagarajan, "Internet Group Management Protocol, Version 3",
         RFC 3376, October 2002.

   [8]   Deering, S., Fenner, W., and B. Haberman, "Multicast Listener
         Discovery (MLD) for IPv6", RFC 2710, October 1999.

   [9]   Vida, R. and L. Costa, "Multicast Listener Discovery Version 2
         (MLDv2) for IPv6", RFC 3810, June 2004.

   [10]  Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
         Neighbor Discovery (SEND)", RFC 3971, March 2005.

   [11]  Kent, S. and R. Atkinson, "IP Encapsulating Security Payload
         (ESP)", RFC 2406, November 1998.

   [12]  Haberman, B., "Allocation Guidelines for IPv6 Multicast
         Addresses", RFC 3307, August 2002.

10.2.  Informative Reference

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

Authors' Addresses

   Brian Haberman
   Johns Hopkins University Applied Physics Lab
   11100 Johns Hopkins Road
   Laurel, MD  20723-6099
   US

   Phone: +1 443 778 1319
   EMail: brian@innovationslab.net

   Jim Martin
   Netzwert AG
   An den Treptowers 1
   D-12435 Berlin
   Germany

   Phone: +49.30/5 900 80-1180
   EMail: jim@netzwert.ag

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