Operation Manual – Multicast
H3C S3600 Series Ethernet Switches-Release 1510 Chapter 6 IGMP Configuration
6-7
II. IGMP group-specific packets
The query router (querier for short) maintains the IGMP join packets on the interface on
the shared network. After the related features are configured, the IGMP querier will
send IGMP group-specific query packets at the user-defined interval for the
user-defined times when it receives the IGMP leave packets from the hosts.
Suppose a host in a multicast group decides to leave the multicast group. The related
procedure is as follows:
z The host sends an IGMP leave packet.
z When the IGMP querier receives the packet, it will send IGMP group-specific
query packets at the interval configured by the igmp lastmember-queryinterval
command (the interval is 1 second by default) for the robust-value times (the
robust-value argument is configured by the igmp robust-count command and it is
2 by default).
z If other hosts are interested in the group after receiving the IGMP group-specific
query packet from the querier, they will send IGMP join packets in the maximum
response time specified in the packet.
z If the IGMP querier receives IGMP join packets from other hosts within the period
of robust-value x lastmember-queryinterval, it will maintain the membership of the
group.
z If the IGMP querier does not receive IGMP join packets from other hosts after the
period of robust-value x lastmember-queryinterval, it considers that the group has
timed out and will not maintain the membership of the group.
Note:
You can use the igmp max-response-time command to set the maximum response
time for general IGMP query packets, while that of an IGMP group-specific query
packet is determined by the following expression:robust-value x
lastmember-queryinterval.
The procedure is only fit for the occasion where IGMP queriers run IGMP version 2.
If the host runs IGMP version 1, it does not send IGMP leave messages when leaving a
group, so the conditions will be the same as described in the procedure above.
III. IGMP querier substitution rules
In a network segment containing multiple IGMP-enabled interfaces, the one with the
least IP address becomes the IGMP querier. If no query message is received within the
period specified by the igmp timer other-querier-present command, the current
IGMP querier is considered to be invalid. In this case, the interface with the second
least IP address becomes the IGMP queerer instead.
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