Huawei Quidway S3900 Series Operation Manual page 403

Operation Manual – Multicast Protocol
Quidway S3900 Series Ethernet Switches-Release 1510
also sends query packets periodically. When it receives the IGMP join packets of a
group member, it will refresh the membership information of the network segment.
II. IGMP group-specific packets
The query router (querier for short) maintains the IGMP joins 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:
The host sends an IGMP leave packet.
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).
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.
If the IGMP querier receives IGMP join packets from other hosts within the
robust-value x seconds time, it will maintain the membership of the group.
If the IGMP querier does not receive IGMP join packets from other hosts after the
robust-value x seconds time, it considers the group times out and will not maintain
the membership of the group.
The procedure is only fit for the occasion when IGMP queriers runs 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
The lifetime of an IGMP querier is limited. When the IGMP querier times out, the querier
will stop sending query messages and another router will replace the IGMP querier.
IV. The maximum query time of IGMP packets
When the host receives a query message, it will set a timer for each of its multicast
groups. The timer value is selected from 0 to the maximum response time at random.
When the value of a timer decreases to 0, the host will send the membership
information of the multicast group.
Through configuring the reasonable maximum response time, you can enable the host
to respond to the query information quickly and enable the Layer 3 switch to understand
the membership information of multicast groups quickly.
Huawei Technologies Proprietary
6-7
Chapter 6 IGMP Configuration