R3303-HP HSR6800 Routers IP Multicast Configuration Guide

15
Timer Description
Message before
ex
p
iration
Action after expiration
Dynamic member
port aging timer.
When a port dynamically
joins a multicast group, the
router starts an aging timer for
the port. When the timer
expires, the dynamic member
port ages out.
IGMP membership
report.
The router removes this
port from the IGMP
snooping forwarding
table.
NOTE:
In IGMP snooping, only dynamic ports age out. Static ports never age out.
How IGMP snooping works
An IGMP snooping-enabled router performs different actions when it receives different IGMP messages.
The ports in this section are dynamic ports. For information about how to configure and remove static
ports, see "Configuring static ports."
When receiving a general query
The IGMP querier periodically sends IGMP general queries to all hosts and routers (224.0.0.1) on the
local subnet to determine whether any active multicast group members exist on the subnet.
After receiving an IGMP general query, the router forwards it to all ports in the VLAN, except the port that
received the query. The router also performs one of the following actions:
• If the receiving port is a dynamic router port in the router port list, restarts the aging timer for the
port.
• If the receiving port is not in the router port list, adds it into the router port list as a dynamic router
port and starts an aging timer for the port.
When receiving a membership report
A host sends an IGMP report to the IGMP querier for the following purposes:
• Responds to an IGMP query if the host is a multicast group member.
• Applies for joining a multicast group.
After receiving an IGMP report, the router forwards it through all the router ports in the VLAN, resolves
the address of the reported multicast group, and performs the following actions:
• If no forwarding entry matches the group address, the router creates a forwarding entry for the
group, adds the port that received the IGMP report as a dynamic member port to the forwarding
entry, and starts an aging timer for the port.
• If a forwarding entry matches the group address, but the port that received the IGMP report is not
in the forwarding entry for the group, the router adds the port as a dynamic member port to the
forwarding entry, and starts an aging timer for the port.
• If a forwarding entry matches the group address and the port that received the IGMP report is in the
forwarding entry for the group, the router restarts the aging timer for the port.
A router does not forward an IGMP report through a non-router port. If the router forwards a report
message through a member port, the IGMP report suppression mechanism causes all attached hosts that
monitor the reported multicast address to suppress their own reports. This makes the router unable to