rfc3376.txt

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Cain, et. al.               Standards Track                    [Page 11]

RFC 3376                         IGMPv3                     October 2002


4.1.11. Query Variants

   There are three variants of the Query message:

   1. A "General Query" is sent by a multicast router to learn the
      complete multicast reception state of the neighboring interfaces
      (that is, the interfaces attached to the network on which the
      Query is transmitted).  In a General Query, both the Group Address
      field and the Number of Sources (N) field are zero.

   2. A "Group-Specific Query" is sent by a multicast router to learn
      the reception state, with respect to a *single* multicast address,
      of the neighboring interfaces.  In a Group-Specific Query, the
      Group Address field contains the multicast address of interest,
      and the Number of Sources (N) field contains zero.

   3. A "Group-and-Source-Specific Query" is sent by a multicast router
      to learn if any neighboring interface desires reception of packets
      sent to a specified multicast address, from any of a specified
      list of sources.  In a Group-and-Source-Specific Query, the Group
      Address field contains the multicast address of interest, and the
      Source Address [i] fields contain the source address(es) of
      interest.

4.1.12. IP Destination Addresses for Queries

   In IGMPv3, General Queries are sent with an IP destination address of
   224.0.0.1, the all-systems multicast address.  Group-Specific and
   Group-and-Source-Specific Queries are sent with an IP destination
   address equal to the  multicast address of interest.  *However*, a
   system MUST accept and  process any Query whose IP Destination
   Address field contains *any* of the addresses (unicast or multicast)
   assigned to the interface on which the Query arrives.

4.2. Version 3 Membership Report Message

   Version 3 Membership Reports are sent by IP systems to report (to
   neighboring routers) the current multicast reception state, or
   changes in the multicast reception state, of their interfaces.
   Reports have the following format:











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RFC 3376                         IGMPv3                     October 2002


       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 = 0x22  |    Reserved   |           Checksum            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           Reserved            |  Number of Group Records (M)  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      .                                                               .
      .                        Group Record [1]                       .
      .                                                               .
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      .                                                               .
      .                        Group Record [2]                       .
      .                                                               .
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                               .                               |
      .                               .                               .
      |                               .                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      .                                                               .
      .                        Group Record [M]                       .
      .                                                               .
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+






















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RFC 3376                         IGMPv3                     October 2002


   where each Group Record has the following internal format:

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Record Type  |  Aux Data Len |     Number of Sources (N)     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Multicast Address                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Source Address [1]                      |
      +-                                                             -+
      |                       Source Address [2]                      |
      +-                                                             -+
      .                               .                               .
      .                               .                               .
      .                               .                               .
      +-                                                             -+
      |                       Source Address [N]                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      .                                                               .
      .                         Auxiliary Data                        .
      .                                                               .
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.2.1. Reserved

   The Reserved fields are set to zero on transmission, and ignored on
   reception.

4.2.2. Checksum

   The Checksum is the 16-bit one's complement of the one's complement
   sum of the whole IGMP message (the entire IP payload).  For computing
   the checksum, the Checksum field is set to zero.  When receiving
   packets, the checksum MUST be verified before processing a message.

4.2.3. Number of Group Records (M)

   The Number of Group Records (M) field specifies how many Group
   Records are present in this Report.

4.2.4. Group Record

   Each Group Record is a block of fields containing information
   pertaining to the sender's membership in a single multicast group on
   the interface from which the Report is sent.





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RFC 3376                         IGMPv3                     October 2002


4.2.5. Record Type

   See section 4.2.12, below.

4.2.6. Aux Data Len

   The Aux Data Len field contains the length of the Auxiliary Data
   field in this Group Record, in units of 32-bit words.  It may contain
   zero, to indicate the absence of any auxiliary data.

4.2.7. Number of Sources (N)

   The Number of Sources (N) field specifies how many source addresses
   are present in this Group Record.

4.2.8. Multicast Address

   The Multicast Address field contains the IP multicast address to
   which this Group Record pertains.

4.2.9. Source Address [i]

   The Source Address [i] fields are a vector of n IP unicast addresses,
   where n is the value in this record's Number of Sources (N) field.

4.2.10. Auxiliary Data

   The Auxiliary Data field, if present, contains additional information
   pertaining to this Group Record.  The protocol specified in this
   document, IGMPv3, does not define any auxiliary data.  Therefore,
   implementations of IGMPv3 MUST NOT include any auxiliary data (i.e.,
   MUST set the Aux Data Len field to zero) in any transmitted Group
   Record, and MUST ignore any auxiliary data present in any received
   Group Record.  The semantics and internal encoding of the Auxiliary
   Data field are to be defined by any future version or extension of
   IGMP that uses this field.

4.2.11. Additional Data

   If the Packet Length field in the IP header of a received Report
   indicates that there are additional octets of data present, beyond
   the last Group Record, IGMPv3 implementations MUST include those
   octets in the computation to verify the received IGMP Checksum, but
   MUST otherwise ignore those additional octets.  When sending a
   Report, an IGMPv3 implementation MUST NOT include additional octets
   beyond the last Group Record.





Cain, et. al.               Standards Track                    [Page 15]

RFC 3376                         IGMPv3                     October 2002


4.2.12. Group Record Types

   There are a number of different types of Group Records that may be
   included in a Report message:

   o A "Current-State Record" is sent by a system in response to a Query
     received on an interface.  It reports the current reception state
     of that interface, with respect to a single multicast address.  The
     Record Type of a Current-State Record may be one of the following
     two values:

        Value  Name and Meaning
        -----  ----------------

          1    MODE_IS_INCLUDE - indicates that the interface has a
               filter mode of INCLUDE for the specified multicast
               address.  The Source Address [i] fields in this Group
               Record contain the interface's source list for the
               specified multicast address, if it is non-empty.

          2    MODE_IS_EXCLUDE - indicates that the interface has a
               filter mode of EXCLUDE for the specified multicast
               address.  The Source Address [i] fields in this Group
               Record contain the interface's source list for the
               specified multicast address, if it is non-empty.

   o A "Filter-Mode-Change Record" is sent by a system whenever a local
     invocation of IPMulticastListen causes a change of the filter mode
     (i.e., a change from INCLUDE to EXCLUDE, or from EXCLUDE to
     INCLUDE), of the interface-level state entry for a particular
     multicast address.  The Record is included in a Report sent from
     the interface on which the change occurred.  The Record Type of a
     Filter-Mode-Change Record may be one of the following two values:

          3    CHANGE_TO_INCLUDE_MODE - indicates that the interface
               has changed to INCLUDE filter mode for the specified
               multicast address.  The Source Address [i] fields
               in this Group Record contain the interface's new
               source list for the specified multicast address,
               if it is non-empty.

          4    CHANGE_TO_EXCLUDE_MODE - indicates that the interface
               has changed to EXCLUDE filter mode for the specified
               multicast address.  The Source Address [i] fields
               in this Group Record contain the interface's new
               source list for the specified multicast address,
               if it is non-empty.




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RFC 3376                         IGMPv3                     October 2002


   o A "Source-List-Change Record" is sent by a system whenever a local
     invocation of IPMulticastListen causes a change of source list that
     is *not* coincident with a change of filter mode, of the
     interface-level state entry for a particular multicast address.
     The Record is included in a Report sent from the interface on which
     the change occurred.  The Record Type of a Source-List-Change
     Record may be one of the following two values:

          5    ALLOW_NEW_SOURCES - indicates that the Source Address
               [i] fields in this Group Record contain a list of the
               additional sources that the system wishes to
               hear from, for packets sent to the specified
               multicast address.  If the change was to an INCLUDE
               source list, these are the addresses that were added
               to the list; if the change was to an EXCLUDE source
               list, these are the addresses that were deleted from
               the list.

          6    BLOCK_OLD_SOURCES - indicates that the Source Address