IGMP
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... groups. It requires implementation of the
Internet Group Management Protocol (IGMP) and extension of the IP and
local network service ...
... ICMP
and (for level 2 hosts) IGMP are considered to be implemented within
the IP module, and the mapping of IP addresses ...
...
The IP module must also be extended to implement the IGMP protocol,
specified in Appendix I. IGMP is used to keep neighboring multicast
routers ...
... IP module must also be extended to implement the IGMP protocol,
specified in Appendix I. IGMP is used to keep neighboring multicast
routers informed of the host group ...
... group memberships present on a
particular local network. To support IGMP, every level 2 host must
join ...
... hosts group at all times because (1) it is simpler, (2) the
frequency of reception of unnecessary IGMP queries should be low
enough that overhead ...
... APPENDIX I. INTERNET GROUP MANAGEMENT PROTOCOL (IGMP) ...
... group memberships to any immediately-neighboring
multicast routers. IGMP is an asymmetric protocol and is specified
here from the point of view of a host, rather than a multicast
router ...
... here from the point of view of a host, rather than a multicast
router. (IGMP may also be used, symmetrically or asymmetrically,
between multicast routers. Such use is not specified here.)
...
... hosts conforming to level 2 of the IP multicasting
specification. IGMP messages are encapsulated in IP datagrams, with
...
... IP datagrams, with
an IP protocol number of 2. All IGMP messages of concern to hosts
have the following format:
...
...
This memo specifies version 1 of IGMP. Version 0 is specified
in RFC-988(-> 1112std5 | 1054(-> 1112std5)) ...
... bit one's complement of the one's
complement sum of the 8-octet IGMP message. For computing
the checksum, the checksum field ...
... group address in its IP destination field and its IGMP group address
field, to ensure that the host ...
... host's own Report is not cancelled by an
erroneous received Report. A host should quietly discard any IGMP
message of type other than Host Membership Query ...
... network. Queries are normally sent infrequently
(no more than once a minute) so as to keep the IGMP overhead on hosts
...
... network with no multicast routers present, the only
IGMP traffic is the one or more Reports sent whenever a host joins a
...
...
IGMP behavior is more formally specified by the state transition
diagram below. A host may be in one of three possible states, with
...
... "report received" occurs when the host receives a valid IGMP
Host Membership Report message. To be valid ...
... valid, the Report
message must be at least 8 octets long, have a correct IGMP
checksum, and contain the same IP ...
... IP
destination field and its IGMP group address field. A Report
applies only to the membership in the group ...
...
All other events, such as receiving invalid IGMP messages, or IGMP
messages other than Query or Report, are ignored in all states.
...
... All other events, such as receiving invalid IGMP messages, or IGMP
messages other than Query or Report, are ignored in all states.
...