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   IDMR Working Group                                            S. Biswas
   Internet Draft                                          Nortel Networks
   draft-ietf-idmr-igmp-mrdisc-10.txt                              B. Cain
   January 2003                                           Storigen Systems
   Expires July 2003                                           B. Haberman
                                                          Caspian Networks


                       Multicast Router Discovery


Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that
   other groups may also distribute working documents as Internet-
   Drafts. Internet-Drafts are draft documents valid for a maximum of
   six months and may be updated, replaced, or obsoleted by other
   documents at any time. It is inappropriate to use Internet- Drafts
   as reference material or to cite them other than as "work in
   progress."

   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.


Abstract

   The concept of IGMP snooping requires the ability to identify the
   location of multicast routers.  Since IGMP (and MLD) snooping is not
   standardized, there are many mechanisms in use to identify the
   multicast routers.  However, this scenario can lead to
   interoperability issues between multicast routers and layer-2
   switches from different vendors.

   This document introduces a general mechanism that allows for the
   discovery of multicast routers.  By introducing these new messages,
   snooping devices have a uniform means of identifying multicast
   routers without dependency on particular routing protocols.  These
   messages may also be used to convey configuration parameters to all
   systems on a network.  In addition, other devices that may need to
   discover multicast routers can utilize these messages.

Table of Contents

   1. Introduction....................................................2
   2. Protocol Overview...............................................3

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   3. Multicast Router Advertisement..................................4
   3.1 Overview.......................................................4
   3.2 IP Header Fields...............................................4
   3.3 Multicast Router Advertisement Message Format..................5
   3.4 Sending Multicast Router Advertisements........................6
   3.5 Receiving Multicast Router Advertisements......................6
   3.6 Multicast Router Advertisement Configuration Variables.........7
   4. Multicast Router Solicitation...................................8
   4.1 Overview.......................................................8
   4.2 IP Header Fields...............................................8
   4.3 Multicast Router Solicitation Message Format...................9
   4.4 Sending Multicast Router Solicitations.........................9
   4.5 Receiving Multicast Router Solicitations.......................9
   4.6 Multicast Router Solicitation Configuration Variables.........10
   5. Multicast Router Termination...................................10
   5.1 Overview......................................................10
   5.2 IP Header Fields..............................................10
   5.3 Multicast Router Termination Message Format...................10
   5.4 Sending Multicast Router Termination Messages.................11
   5.5 Receiving Multicast Router Termination Messages...............11
   6. Multicast Router Discovery Protocol Constants..................11
   7. Mandatory Advertisement Options................................11
   7.1 Overview of Options...........................................11
   7.2 Query Interval Advertisement Option...........................12
   7.3 Robustness Variable Advertisement Option......................12
   8. IPv6 Support...................................................13
   8.1 Router Advertisement Message..................................13
   8.2 Router Solicitations..........................................14
   9. Security Considerations........................................14
   10. IANA Considerations...........................................14
   11. Acknowledgements..............................................15
   12. References....................................................15
   13. Authors' Addresses............................................15
   14. Full Copyright Statement......................................16


1. Introduction

   Multicast router discovery messages are useful for discovering
   multicast capable routers.  This capability is useful in a layer-2
   bridging domain with "snooping" type of schemes.  By listening to
   multicast router discovery messages, layer-2 devices can determine
   where to send multicast source data and IGMP Host Membership Reports
   [RFC1112] [RFC2236].  Multicast source data and IGMP Host Membership
   Reports must be received by all multicast routers on a segment.
   Using IGMP Host Membership Queries to discover multicast routers is
   not useful because of query suppression in IGMP.

   The use of the multicast router advertisement is not precluded from
   being used for other purposes.  Extensible options have been included
   in the advertisement message for future enhancements.


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   The following are justifications for inventing another router
   discovery protocol:

           ¡ Using ICMP router discovery is not an appropriate solution
              for multicast router discovery because: 1.) It may confuse
              hosts listening to ICMP router advertisements; unicast and
              multicast topologies may not be congruent.  2.) There is
              no way to tell from an ICMP router advertisement if a
              router is running a multicast routing protocol.

           ¡ By making multicast router discovery messages extensible,
              future enhancements can be made.

           ¡ By inventing a generic IP layer message, multiple types of
              messages per link layer are not needed (i.e. including
              this functionality as part of IP is better than inventing
              N discovery protocols for N layer-2 technologies).

   Although multicast router discovery messages could be sent as ICMP
   messages, IGMP was chosen because IGMP snooping switches already
   snoop IGMP messages and the protocol is multicast specific.

   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. Protocol Overview

   IGMP 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 Multicast Router Advertisements from multicast routers.  The
   Multicast Router Termination message is sent when a router terminates
   its multicast routing functions.

   Multicast routers send Multicast Router Advertisements (hereafter
   called advertisements) periodically on all interfaces on which
   multicast forwarding is enabled.  Advertisements are also sent in
   response to Multicast Router Solicitations (hereafter called
   solicitations).

   Multicast Router Solicitations are sent whenever a device wishes to
   discover multicast routers on a directly attached subnet.

   Multicast Router Terminations (hereafter called terminations) are
   sent when a router terminates its multicast routing functions.



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   All IGMP Multicast Router Discovery messages are sent with an IP TTL
   of 1 and contain the IP Router Alert Option [RFC2113] in their IP
   header.

   Advertisement and termination messages are sent to the All-Systems
   multicast group (224.0.0.1).

   Solicitation messages are sent to the All-Routers multicast group
   (224.0.0.2).

   Both IP (e.g. layer-3 switches) and non-IP forwarding devices (e.g.
   layer-2 switches) may send Multicast Router Solicitations to solicit
   Multicast Router Advertisements.


3. Multicast Router Advertisement

  3.1 Overview

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

   Router advertisements are sent upon expiration of a periodic timer,
   when a router starts up, and when a router interface (that has IP
   multicast forwarding enabled) initializes/restarts. Advertisements
   are sent as IGMP messages to the All-Systems multicast address
   (224.0.0.1) and SHOULD be rate-limited.

   Router advertisements may contain any number of options.  Two options
   are defined in this document and MUST be supported by any
   implementation of IGMP multicast router discovery.  These options are
   described in Section 5.  Additional options may be defined as needed
   by future work.


  3.2 IP Header Fields

  3.2.1 Source Address

   An IP address belonging to the interface from which this message is
   sent.  If multiple source addresses are configured on an interface,
   then the one chosen is implementation dependent.

  3.2.2 Destination Address

   Router Advertisements are sent to the All-Systems multicast address
   (224.0.0.1).

  3.2.3 Time-to-Live


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   The Time-to-Live field MUST be 1.

  3.2.4 Protocol

   The protocol field is set to IGMP (2).

  3.3 Multicast Router Advertisement Message 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            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Unused            |     Number of Options (N)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Option [1] (TLV encoded)                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Option [...] (TLV encoded)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Option [N] (TLV encoded)                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


  3.3.1 Type Field

   The type field is set to XX (to be assigned by IANA).

  3.3.2 Advertisement Interval

   This specifies the periodic time interval at which Multicast Router
   Advertisements are sent in units of seconds.  This value is set to
   the configured MaxAdvertisementInterval variable.

  3.3.3 Checksum

   The checksum is the 16-bit one's complement of the one's complement
   sum of the IGMP message, starting with the IGMP type.  For computing
   the checksum, the Checksum field is set to 0.

  3.3.4 Number of Options (N)

   The number of options contained in the router advertisement. If no
   options are sent this field MUST be set to 0.

  3.3.5 Option[1..N]

   Options are encoded as TLV in the following manner:






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        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      |    Length     |           Value               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   If the Number of Options field is not zero, a receiver MUST examine
   all options.  No strict ordering of options is enforced.

       Type: Set to option type being advertised

       Length: Length in bytes of Value field

       Value: Option dependent value

  3.4 Sending Multicast Router Advertisements

   Router Advertisements are sent when the following events occur:

           ¡ When the periodic advertisement interval timer expires.
              Note that it is not strictly periodic because the
              advertisement interval is a random number between
              MaxAdvertisementInterval and MinAdvertisementInterval.

           ¡ After waiting for a random delay less than
              MaxInitialAdvertisementInterval when an interface first
              comes up, is (re)initialized, or IGMP Multicast Router
              Discovery is enabled.  A router may send up to a maximum
              of MaxInitialAdvertisements advertisements, waiting for a
              random delay less than MaxInitialAdvertisementInterval
              between each successive advertisement.  Multiple messages
              are sent for robustness in the face of packet loss on the
              network.

   This is to prevent an implosion of router advertisements.  An example
   of this occurring would be when many routers are powered on at the
   same time.  When a solicitation is received, a router advertisement
   is sent in response with a random delay less than MAX_RESPONSE_DELAY.
   If a solicitation is received while an advertisement is pending
   (because of a recent solicitation), that solicitation will be
   ignored.

   Whenever an advertisement is sent, the periodic advertisement
   interval timer must be reset.

  3.5 Receiving Multicast Router Advertisements

   Upon receiving a router advertisement, devices will validate the
   message by the following criteria:

     1. Verifying the IGMP checksum

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     2. IP Destination Address = All-Systems multicast address

   A router advertisement not meeting the validity requirements should
   be silently discarded or logged in a rate-limited manner. Devices
   MUST process all options, discarding options that are not recognized.

   If a router advertisement is not received for a particular neighbor
   within NeighborDeadInterval time interval, then the neighbor is
   considered to be unreachable.

  3.6 Multicast Router Advertisement Configuration Variables

   A router that implements multicast router discovery MUST allow for
   the following variables to be configured by system management;
   default values are specified so as to make it unnecessary to
   configure any of these variables in many cases.

   For each interface the following configurable variables are defined:

  3.6.1 MaxAdvertisementInterval

   The maximum time allowed between sending router advertisements from
   the interface, in seconds. Must be no less than 2 seconds and no
   greater than 180 seconds.

   Default: 20 seconds.

  3.6.2 MinAdvertisementInterval

   The minimum time allowed between sending unsolicited router
   advertisements from the interface, in seconds. Must be no less than 3
   seconds and no greater than MaxAdvertisementInterval.

   Default: 0.75 * MaxAdvertisementInterval

  3.6.3 MaxInitialAdvertisementInterval

   The first router advertisement out of an interface is sent after
   waiting for a random interval less than this variable. This will
   prevent a flood of router advertisements when many routers start up
   at the same time.

   Default: 2 seconds

  3.6.4 MaxInitialAdvertisements

   The maximum number of router advertisements that will be sent on a
   subnet after a router boots.

   Default: 3


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  3.6.5 NeighborDeadInterval

   The maximum time allowed before a neighbor can be declared "dead".
   This variable is defined in seconds. In order for all devices to have
   a consistent state, it is necessary for the MaxAdvertisementInterval
   to be configured the same on all devices on the subnet.

   Default: 3 * MaxAdvertisementInterval

4. Multicast Router Solicitation

  4.1 Overview

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

   Router solicitations may be sent when a device starts up, when an
   interface (re)initializes, or when IGMP Multicast Router Discovery is
   enabled.  Solicitations are sent as IGMP messages to the All-Routers
   multicast address (224.0.0.2) and SHOULD be rate-limited.

  4.2 IP Header Fields

  4.2.1 Source Address

   An IP address belonging to the interface from which this message is
   sent.  If multiple source addresses are configured on an interface,
   then the one chosen is implementation dependent.

   If the solicitation is being sent from a device that does not have an
   IP address (i.e. non-managed layer-2 switch), then the source address
   should be set to all zeros.

  4.2.2 Destination Address

   Solicitation messages are sent to the All-Routers multicast address
   (224.0.0.2).

  4.2.3 Time-to-Live

   The time-to-live field MUST be 1.

  4.2.4 Protocol

   The protocol field is set to IGMP (2).



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  4.3 Multicast Router Solicitation Message 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            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  4.3.1 Type Field

   The type field is set to YY (to be assigned by IANA).

  4.3.2 Reserved Field

   Sent as 0; ignored on reception.

  4.3.3 Checksum

   The checksum is the 16-bit one's complement of the one's complement
   sum of the IGMP message, starting with the IGMP type.  For computing
   the checksum, the Checksum field is set to 0.

  4.4 Sending Multicast Router Solicitations

   Router solicitations are sent when the following events occur:

     1. After waiting for a random delay less than SOLICITATION_INTERVAL
        when an interface first comes up, is (re)initialized, or IGMP
        Multicast Router Discovery is enabled.  A device may send up to
        a maximum of MAX_SOLICITATIONS, waiting for a random delay less
        than SOLICITATION_INTERVAL between each successive solicitation.

     2. Optionally, for an implementation specific event. Solicitations
        MUST be rate-limited; no more than MAX_SOLICITATIONS MUST be
        sent in SOLICITATION_INTERVAL seconds.

  4.5 Receiving Multicast Router Solicitations

   Upon receiving a router solicitation, routers will validate the
   message by:

     1. Verifying the IGMP checksum

     2. IP Destination Address = All-Routers multicast address

   A router solicitation not meeting the validity requirements should be
   silently discarded or logged in a rate-limited manner.

   Solicitation message IP source addresses MUST NOT be used as part of
   the validity check.


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  4.6 Multicast Router Solicitation Configuration Variables

   There are no configurable variables with respect to router
   solicitations.

5. Multicast Router Termination

  5.1 Overview

   The Multicast Router Termination message is used to expedite the
   notification of a change in the status of a routers multicast
   forwarding functions.

  5.2 IP Header Fields

  5.2.1 Source Address

   An IP address belonging to the interface from which this message is
   sent.  If multiple source addresses are configured on an interface,
   then the one chosen is implementation dependent.

  5.2.2 Destination Address

   Multicast Router Termination messages are sent to the All-Systems
   multicast address (224.0.0.1).

  5.2.3 Time-to-Live

   The Time-to-Live field MUST be 1.

  5.2.4 Protocol

   The protocol field is set to IGMP (2).

  5.3 Multicast Router Termination Message 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            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  5.3.1 Type Field

   The type field is set to ZZ (to be assigned by IANA).

  5.3.2 Reserved Field

   Sent as 0; ignored on reception.

  5.3.3 Checksum

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   The checksum is the 16-bit one's complement of the one's complement
   sum of the IGMP message, starting with the IGMP type.  For computing
   the checksum, the Checksum field is set to 0.

  5.4 Sending Multicast Router Termination Messages

   Multicast Router Termination messages are sent for three reasons:

     1. Multicast forwarding is disabled on the interface

     2. The interface is administratively disabled

     3. The router is gracefully shutdown

  5.5 Receiving Multicast Router Termination Messages

   Upon receiving a termination message, routers will validate the
   message by the following criteria:

     1. Verifying the IGMP checksum

     2. IP Destination Address = All-Systems multicast address

   A termination message not meeting the validity requirements should be
   silently discarded or logged in a rate-limited manner.

6. Multicast Router Discovery Protocol Constants

   The following list identifies constants used in the Multicast Router
   Discovery protocol.  These constants are used in the calculation of
   parameters.

           ¡ MAX_RESPONSE_DELAY                   2 seconds

           ¡ MAX_SOLICITATION_DELAY               1 second

           ¡ SOLICITATION_INTERVAL                3 seconds

           ¡ MAX_SOLICITATIONS                    3 transmissions

7. Mandatory Advertisement Options

  7.1 Overview of Options

   The following options MUST be supported by an implementation of
   Multicast Router Discovery: Query Interval Advertisement Option and
   Robustness Variable Advertisement Option.  These options advertise
   specific group management variables on a per-interface basis.
   Although no requirements exist for multicast routers at this time, it


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   is assumed that all multicast routers support a group management
   protocol.

  7.2 Query Interval Advertisement Option

        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=x      |  Length=2     |      IGMP Query Interval      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           ¡ For IPv4, x=1
           ¡ For IPv6, x=n (to be assigned by IANA)

   If a multicast router has any version of IGMP or MLD [RFC2710, MLDv2]
   enabled on an interface on which Multicast Router Discovery is also
   enabled, it MUST send all advertisements with the Query Interval
   Advertisement Option.  This option contains the IGMP/MLD "Query
   Interval" configured on the interface on which advertisements are
   sent.

   This option is sent regardless of whether the router is currently the
   IGMP querier for the subnet.

   IGMP Query Interval field is equal (in seconds) to the configured
   IGMP/MLD "query interval" on the interface from which the
   advertisement was sent.

  7.3 Robustness Variable Advertisement Option

        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=y      |  Length=2     |     Robustness Variable       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              ¡ For IPv4, y=2
              ¡ For IPv6, y=m (to be assigned by IANA)

   If a multicast router has IGMPv2 [IGMPv2], IGMPv3 [IGMPv3] or MLD
   [RFC2710, MLDv2] enabled on an interface on which IGMP Multicast
   Router Discovery is also enabled, it MUST send all advertisements
   with the Robustness Variable Advertisement Option.  This option
   contains the IGMP/MLD "Robustness Variable" configured on the
   interface on which advertisements are sent.

   This option is sent regardless of whether the router is currently the
   IGMP querier for the subnet.  This option may be omitted if IGMPv1 is
   enabled on the interface.



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   Robustness Variable is an integer that MUST not be zero
   [IGMPv2][RFC2710] and is equal to the IGMPv2/MLDv1 robustness
   variable.

8. IPv6 Support

   The Multicast Router Discovery function for IPv6 is accomplished
   using the Neighbor Discovery Protocol for IPv6 [RFC2461] (hereafter
   called NDP).  Specifically, the Router Advertisement message contains
   new fields to support the discovery of multicast routers.  For this
   reason, the timing mechanisms defined for NDP will be used instead of
   those defined in this document for IPv4 support.  It should be noted
   that the options defined in section 7 are not mandatory for IPv6
   support.

  8.1 Router Advertisement Message

   The Router Advertisement message contains two new fields to support
   the multicast router discovery mechanism.  The modified message
   format is:

        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      |     Code      |          Checksum             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Cur Hop Limit |M|O|H|D|E|Rsrvd|       Router Lifetime         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Reachable Time                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          Retrans Timer                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Options ...
       +-+-+-+-+-+-+-+-+-+-+-+-

   The two new fields are the 'D' and 'E' bits.  All other fields retain
   their definitions and functions as described in Section 4.2 of the
   NDP specification [RFC2461].

  8.1.1 Discovery (D) bit

   The 'D' bit is used by a router to indicate support for the Multicast
   Router Discovery protocol.  A value of '1' indicates that the router
   supports the discovery protocol.  A value of '0' indicates no
   support.  This allows for backwards compatibility of the Router
   Advertisement message.

  8.1.2 Enabled (E) bit

   The 'E' bit indicates whether multicast routing is enabled on the
   router's interface.  A value of '1' indicates that multicast

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   forwarding is enabled on the router's interface.  A value of '0'
   indicates that multicast forwarding is disabled.

   When the state of multicast forwarding changes on an interface, a
   router must stop its Router Advertisement timer, transmit a Router
   Advertisement with the 'E' bit set to the value associated with the
   new multicast forwarding state, and restart its Router Advertisement
   timer.

  8.2 Router Solicitations

   An NDP Router Solicitation message can be sent to solicit a Router
   Advertisement message in order to determine the multicast forwarding
   state of a router.  The periodic transmission of solicitation
   messages is outlined in RFC 2461.

9. Security Considerations

   The Multicast Router Advertisement message may allow rogue machines
   to masquerade as multicast routers.  This could allow those machines
   to eavesdrop on multicast data transmission or create a denial of
   service attack on multicast flows.  However, these new messages are
   extensible and that allows for the introduction of security
   associations into the protocol.  These security extensions could be
   used to authenticate or encrypt the messages.

10. IANA Considerations

   This document introduces three new IGMP messages.  Each of these
   messages requires a new IGMP 'Type' value.  This document requests
   IANA to assign three new IGMP 'Type' values to the Multicast Router
   Discovery protocol (for Advertisements, Solicitations, and
   Terminations).

   IPv6 support requests the allocation of two new Neighbor Discovery
   Option Types to support the mandatory Multicast Router Discovery
   options (found in Sections 7.2 and 7.3).

   IPv4 support of this protocol requires the administration of the
   Multicast Router Discovery option space.  This document requests that
   options be allocated using an IESG Approval or Standards Action
   processes.  In addition, this document requests that the options
   defined, the Query Interval Advertisement option (Section 7.2) and
   the Robustness Variable Advertisement option (Section 7.3) be
   allocated the values specified in the respective sections.

   This protocol also requests the creation of a new IANA registry to
   manage the Multicast Router Discovery Code Values for IPv4 support.
   New Code Values for the Multicast Router Discovery Type values are
   allocated using IESG Approval or Standards Action processes.


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11. Acknowledgements

   ICMP Router Discovery [RFC1256] was used as a general model for IGMP
   Multicast Router Discovery.

12. Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", RFC 2119, BCP 14, March 1997.

   [RFC2236]  Fenner, W., "Internet Group Management Protocol,
              Version 2", RFC 2236, November 1997.

   [IGMPv3]   Cain, B., et al, "Internet Group Management Protocol,
              Version 3", RFC 3376, October 2002.

   [RFC2461]  Narten, T., Nordmark, E., and Simpson, W., "Neighbor
              Discovery IP Version 6 (IPv6)", RFC 2461, December 1998.

   [RFC2710]  Deering, S., Fenner, B., and Haberman, B., "Multicast
              Listener Discovery (MLD) for IPv6", RFC 2710, October
              1999.

   [MLDv2]    Vida, R., et al, "Multicast Listener Discovery Version 2
              (MLDv2) for IPv6", work in progress.


13. Informative References

   [RFC1256]  Deering, S., "ICMP Router Discovery Messages", RFC 1256,
              September 1991.

   [RFC1112]  Deering, S., "Host Extensions for IP Multicasting",
              RFC 1112, August 1989.

   [RFC2113]  Katz, D., "IP Router Alert Option," RFC 2113, April 1996.


14. Authors' Addresses

   Shantam Biswas
   Nortel Networks
   600 Technology Park Drive
   Billerica, MA 01821
   Email: sbiswas@baynetworks.com
   Phone: 1-978-916-8048

   Brad Cain
   Storigen Systems

Biswas, Cain, Haberman                                              15


Internet Draft        Multicast Router Discovery          January 2003

   Email: bcain@storigen.com

   Brian Haberman
   Caspian Networks
   1 Park Drive, Suite 300
   Research Triangle Park, NC  27709

   Email: bkhabs@nc.rr.com
   Phone: +1-919-949-4828


15. Full Copyright Statement

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

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   or assist in its implementation may be prepared, copied, published
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   kind, provided that the above copyright notice and this paragraph
   are included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice ore references to the Internet Society or other
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   The limited permissions granted above are perpetual and will not be
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   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
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   This document expires in July, 2003.


Biswas, Cain, Haberman                                              16


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Biswas, Cain, Haberman                                              17


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