Configuring Options Related To Igmp Query Messages - H3C S5600 Series Operation Manual

Operation Manual – Multicast
H3C S5600 Series Ethernet Switches

3.2.4 Configuring Options Related to IGMP Query Messages

I. IGMP general query
An IGMP router sends IGMP general query messages to the local subnet periodically,
and multicast receiver hosts send IGMP reports in response to IGMP queries. Thus the
router learns which multicast groups on the subnet have active members.
II. IGMP group-specific query
On a multi-access network, the query router (querier for short) maintains group
memberships. After the related features are configured, the IGMP querier sends a
configurable number of IGMP group-specific queries at a configurable interval when it
receives an IGMP leave message 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 message.
When the IGMP querier receives the message, it sends robust-value IGMP
group-specific query messages at the interval of lastmember-queryinterval.
If other hosts are interested in the group after receiving the IGMP group-specific
query message from the querier, they must send IGMP report messages within
the maximum response time specified in the query messages.
If the IGMP querier receives IGMP report messages from other hosts within the
period of robust-value x lastmember-queryinterval, it will maintain the membership
of the group.
If the IGMP querier does not receive IGMP report messages from other hosts after
the period of robust-value x lastmember-queryinterval, it considers that the group
has no members on the local subnet and removes the forwarding table entry for
the group.
Note:
You can use the igmp max-response-time command to set the maximum response
time for general IGMP query messages, while that of an IGMP group-specific query
message is determined by robust-value x lastmember-queryinterval.
The procedure is only fit for the occasion where IGMP queriers run IGMP version 2.
III. IGMP querier election
On a subnet containing multiple IGMP-enabled interfaces, the one with the lowest IP
address becomes the IGMP querier. If non-querier interfaces receive no query
message within the period configured in the igmp timer other-querier-present
3-7
Chapter 3 IGMP Configuration