Operation Manual – Multicast Protocol
H3C S5500-SI Series Ethernet Switches
Chapter 1 IGMP Snooping Configuration
1-4
z
If the receiving port is a router port existing in its router port list, the switch resets
the aging timer of this router port.
z
If the receiving port is not a router port existing in its router port list, the switch adds
it into its router port list and sets an aging timer for this router port.
II. Membership reports
A host sends an IGMP report to the multicast router in the following circumstances:
z
Upon receiving an IGMP query, a multicast group member host responds with an
IGMP report.
z
When intended to join a multicast group, a host sends an IGMP report to the
multicast router to announce that it is to join the multicast group.
Upon receiving the IGMP report, the switch forwards it through all the router ports in the
VLAN and performs the following to the receiving port:
z
Resolves the address of the multicast group that the host is to join and add a
forwarding entry for this port in the forwarding table.
z
Sets or resets a member port aging timer for this port.
Note:
A switch will not forward an IGMP report through a non-router port for the following
reason: When IGMP report suppression is enabled, if member hosts of that multicast
group still exist under non-router ports, the hosts will stop sending reports when they
receive the message, and this prevents the switch from knowing if members of that
multicast group are still attached to these ports.
III. Leave messages
When an IGMPv1 host leaves a multicast group, the host does not send an IGMP leave
message, so the switch cannot know immediately that the host has left the multicast
group. However, as the host stops sending IGMP reports as soon as it leaves a
multicast group, the switch deletes the forwarding entry for the member port
corresponding to the host from the forwarding table when its aging timer expires.
When an IGMPv2 or IGMPv3 host leaves a multicast group, the host sends an IGMP
leave message to the multicast router to announce that it has leaf the multicast group.
Upon receiving an IGMP leave message on the last member port, a switch forwards it
out all router ports in the VLAN. Because the switch does not know whether any other
member hosts of that multicast group still exists under the port to which the IGMP leave
message arrived, the switch does not immediately delete the forwarding entry
corresponding to that port from the forwarding table; instead, it resets the aging timer of
the member port.
