HP 6125G HP 6125G & 6125G/XG Blade Switches IP Multicast Configuration - Page 26
When receiving a leave message, IGMP snooping proxying
View all HP 6125G manuals
Add to My Manuals
Save this manual to your list of manuals |
Page 26 highlights
unable to know whether the reported multicast group still has active members attached to that port. For more information about the IGMP report suppression mechanism, see "Configuring IGMP." When receiving a leave message When an IGMPv1 host leaves a multicast group, the host does not send an IGMP leave message, and the switch cannot know immediately that the host has left the multicast group. However, because the host stops sending IGMP reports as soon as it leaves the multicast group, the switch removes the port that connects to the host from the forwarding entry for the multicast group when the aging timer for the port expires. When an IGMPv2 or IGMPv3 host leaves a multicast group, the host sends an IGMP leave message to the multicast router. When the switch receives an IGMP leave message on a dynamic member port, the switch first examines whether a forwarding entry matches the group address in the message, and, if a match is found, whether the forwarding entry for the group contains the dynamic member port. • If no forwarding entry matches the group address, or if the forwarding entry does not contain the port, the switch directly discards the IGMP leave message. • If a forwarding entry matches the group address and the forwarding entry contains the port, the switch forwards the leave message to all router ports in the VLAN. Because the switch does not know whether any other hosts attached to the port are still listening to that group address, the switch does not immediately remove the port from the forwarding entry for that group. Instead, it restarts the aging timer for the port. After receiving the IGMP leave message, the IGMP querier resolves the multicast group address in the message and sends an IGMP group-specific query to the multicast group through the port that received the leave message. After receiving the IGMP group-specific query, the switch forwards it through all its router ports in the VLAN and all member ports of the multicast group. The switch also performs the following judgment for the port that received the IGMP leave message: • If the port (assuming that it is a dynamic member port) receives an IGMP report in response to the group-specific query before its aging timer expires, it indicates that some host attached to the port is receiving or expecting to receive multicast data for the multicast group. The switch restarts the aging timer for the port. • If the port receives no IGMP report in response to the group-specific query before its aging timer expires, it indicates that no hosts attached to the port are still listening to that group address. The switch removes the port from the forwarding entry for the multicast group when the aging timer expires. IGMP snooping proxying You can configure the IGMP snooping proxying function on an edge device to reduce the number of IGMP reports and leave messages sent to its upstream device. The device configured with IGMP snooping proxying is called an IGMP snooping proxy. It is a host from the perspective of its upstream device. Even though an IGMP snooping proxy is a host from the perspective of its upstream device, the IGMP membership report suppression mechanism for hosts does not take effect on it. For more information about the IGMP report suppression mechanism for hosts, see "Configuring IGMP." 15