HP ProCurve 6108, Management And Configuration Manual

Page: 312 / 547

Multimedia Traffic Control with IP Multicast (IGMP)
How IGMP Operates
■ Report (Join): A message sent by a host to the querier to indicate that
the host wants to be or is a member of a given group indicated in the report
message.
■ Leave Group: A message sent by a host to the querier to indicate that the
host has ceased to be a member of a specific multicast group.
N o t e o n I G M P
When the switch receives an IGMPv3 Join, it accepts the host request and
v e r s i o n 3
begins to forwarding the IGMP traffic. This means ports that have not joined
s u p p o r t
the group and are not connected to routers or the IGMP Querier will not
receive the group's multicast traffic.
The switch does not support the IGMPv3 “Exclude Source” or “Include
Source” options in the Join Reports. Rather, the group is simply joined from
all sources.
The switch does not support becoming a version 3 Querier. It will become a
version 2 Querier in the absence of any other Querier on the network.
An IP multicast packet includes the multicast group (address) to which the
packet belongs. When an IGMP client connected to a switch port needs to
receive multicast traffic from a specific group, it joins the group by sending
an IGMP report (join request) to the network. (The multicast group specified
in the join request is determined by the requesting application running on the
IGMP client.) When a networking device with IGMP enabled receives the join
request for a specific group, it forwards any IP multicast traffic it receives for
that group through the port on which the join request was received. When the
client is ready to leave the multicast group, it sends a Leave Group message
to the network and ceases to be a group member. When the leave request is
detected, the appropriate IGMP device will cease transmitting traffic for the
designated multicast group through the port on which the leave request was
received (as long as there are no other current members of that group on the
affected port).
Thus, IGMP identifies members of a multicast group (within a subnet) and
allows IGMP-configured hosts (and routers) to join or leave multicast groups.
IGMP Data. To display data showing active group addresses, reports, que­
ries, querier access port, and active group address data (port, type, and
access), see “Internet Group Management Protocol (IGMP) Status” on page
B-19.
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