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... Internet Group Management Protocol (IGMP) is used by IP hosts to
report their multicast group memberships to any immediately-
...
... multicast routers. This memo describes only the use of
IGMP between hosts and routers to determine group membership.
...
... Routers that are members of multicast groups are expected to behave
as hosts as well as routers, and may even respond to their own
queries ...
... IGMP is a integral part of IP. It is required to be
implemented by all hosts wishing to receive IP multicasts. IGMP
messages are encapsulated ...
... RFC2113] in their IP
header. All IGMP messages of concern to hosts have the following
format:
...
... routers to tune the "leave
latency" (the time between the moment the last host leaves a group
and when the routing protocol ...
... physical interfaces on a single network this protocol need only run
on one of them. Hosts, on the other hand, need to perform their
actions on all interfaces that have memberships associated with them.
...
... a different random value, using the highest clock granularity
available on the host, selected from the range (0, Max Response Time]
with Max Response Time as specified in the Query ...
... range (0, Max Response Time]
with Max Response Time as specified in the Query packet. When a host
receives a Group-Specific Query ...
... Report to the group, with IP TTL of 1. If the host receives another
host's Report (version 1 ...
... IP TTL of 1. If the host receives another
host's Report (version 1 or 2) while it has a timer running, it stops
...
...
When a host joins a multicast group, it should immediately transmit
an unsolicited Version 2 ...
... When a host leaves a multicast group, if it was the last host to
reply to a Query with a Membership Report for that group ...
... all-routers multicast group
(224.0.0.2). If it was not the last host to reply to a Query, it MAY
send nothing as there must be another member on the subnet ...
... subnet. This is
an optimization to reduce traffic; a host without sufficient storage
to remember whether or not it was the last host to reply MAY always
...
... traffic; a host without sufficient storage
to remember whether or not it was the last host to reply MAY always
send a Leave Group message when it leaves a group ...
... group because other group members have no need to know that a host
has left the group, but it does no harm to address ...
... IGMPv2 host may be placed on a subnet where there are hosts that
have not yet been upgraded to IGMPv2. The following requirement ...
...
The host MUST allow its Membership Report to be suppressed by
either a Version 1 Membership Report or a Version 2 ...
... IGMPv2 router may be placed on a subnet where there are hosts that
have not yet been upgraded to IGMPv2. The following requirements ...
... a timer to note that there are version 1 hosts present which are
members of the group for which it heard the report. This timer ...
... Host State Diagram ...
...
Host behavior is more formally specified by the state transition
diagram below. A host may be in one of three possible states with
...
... Host behavior is more formally specified by the state transition
diagram below. A host may be in one of three possible states with
respect to any single IP multicast group ...
... initial state for all memberships on
all network interfaces; it requires no storage in the host.
...
... Querier is running IGMPv1, this action SHOULD be
skipped. If the flag saying we were the last host to report is
cleared, this action MAY be skipped. The Leave Message is sent to
the ALL-ROUTERS ...
... group (address 224.0.0.1) is handled as a special
case. The host starts in Idle Member state for that group ...
...
In addition, a host may be in one of two possible states with respect
to any single network interface:
...
... "IGMPv1 query received", when the host receives a query with the
Max Response Time field set to 0.
...
... "No Members Present" state, when there are no hosts on the network
which have sent reports for this multicast group ...
... "Members Present" state, when there is a host on the network which
has sent a Membership Report for this multicast group ...
... Version 1 Members Present" state, when there is an IGMPv1 host on
the network which has sent a Version 1 ...
... timer, | | | | expired | |
| start v1 host | v2 report received| | | (send g-s | |
| timer) | (notify routing ...
... subnet; larger values make the
traffic less bursty, as host responses are spread out over a larger
interval. The number of seconds represented by the [Query Response
Interval ...
... The Unsolicited Report Interval is the time between repetitions of a
host's initial report of membership in a group. Default: 10 seconds.
...
... The Version 1 Router Present Timeout is how long a host must wait
after hearing a Version 1 Query ...
... group being
left in the interests of backwards compatibility with such hosts.
In all cases, however, hosts MUST send to the ALL-ROUTERS ...
... backwards compatibility with such hosts.
In all cases, however, hosts MUST send to the ALL-ROUTERS address
...
... Query message sent to a group with members will cause the
hosts which are members of the group to report their memberships.
This causes a small amount of extra traffic ...
... subnet are meaningless, since
joining a group on a host is generally an unprivileged operation,
so a local user may trivially gain the same result without forging
any messages. Forged Report messages from external sources are
...
... interface on which the packet was received. This solution means
that Reports sent by mobile hosts without addresses on the local
subnet ...
... interface on which the
packet was received. This solution means that v1 Reports sent by
mobile hosts without addresses on the local subnet will be
...
... compatibility with
Version 1 hosts, so should only be used in situations where "fast
leave" is critical. This solution protects against forged
...
... interface on which the packet was received. This solution means
that Leave messages sent by mobile hosts without addresses on the
local subnet ...