HP 1910 User Manual

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NOTE:
In IGMP snooping, only dynamic ports age out. Static ports never age out.
How IGMP snooping works
The ports in this section are dynamic ports.
IGMP messages include general query, IGMP report, and leave message. An IGMP snooping-enabled
switch performs differently depending on the message.
General query
The IGMP querier periodically sends IGMP general queries to all hosts and routers identified by the
address 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 switch forwards the query to all ports in the VLAN except the
receiving port. The switch also performs the following actions:
• If the receiving port is a dynamic router port in the router port list, the switch restarts the aging timer
for the port.
• If the receiving port is not in the router port list, the switch adds the port as a dynamic router port
and starts an aging timer for the port.
IGMP report
A host sends an IGMP report to the IGMP querier in the following circumstances:
• Responds to IGMP queries if the host is a multicast group member.
• Applies for a multicast group membership.
After receiving an IGMP report, the switch forwards it out of all the router ports in the VLAN and resolves
the address of the reported multicast group. The switch also performs the following actions:
• If no forwarding entry matches the group address, the switch creates a forwarding entry for the
group, adds the receiving port as a dynamic member port to the forwarding entry, and starts an
aging timer for that port.
• If a forwarding entry matches the group address, but the receiving port is not in the forwarding
entry for the group, the switch adds the port as a dynamic member port to the forwarding entry, and
starts an aging timer for that port.
• If a forwarding entry matches the group address and the receiving port is in the forwarding entry
for the group, the switch resets an aging timer for that port.
A switch does not forward an IGMP report through a non-router port. If the switch forwards a report
through a member port, the IGMP report suppression mechanism running on hosts causes all attached
hosts that monitor the reported multicast address to suppress their own reports. In this case, the switch
cannot determine whether the reported multicast group still has active members attached to that port.
Leave message
An IGMPv1 host silently leaves a multicast group and the switch is not notified of the leave. However,
because the host stops sending IGMP membership reports as soon as it leaves a multicast group, the
switch removes the dynamic member port that connects to the host from the forwarding entry for the
multicast group when the aging timer for the port expires.

HP 1910 Specifications

General

Brand	HP
Model	1910
Category	Switch
Language	English