KB.15.15

the switch automatically retains that IGMP client in its IGMP table and continues forwarding IGMP

traffic to the IGMP client until the Querier triggers confirmation that no other group members exist

on the same port. This delayed leave operation means that the switch continues to transmit

unnecessary multicast traffic through the port until the Querier renews multicast group status.

Forced fast-leave IGMP

When enabled, forced fast-leave IGMP speeds up the process of blocking unnecessary IGMP traffic

to a switch port that is connect ed to multiple end nodes. (This feature does not activate on ports

where the switch detects only one end node.) For example, in Figure 2 (page 28), even if you

configured forced fast-leave on all ports in the switch, the feature would activate only on port A6

(which has multiple end nodes) when a Leave Group request arrived on that port.

When a port having multiple end nodes receives a Leave Group request from one end node for

a given multicast group "X," forced fast-leave activates and waits a small amount of time to receive

a join request from any other group "X" member on that port. If the port does not receive a join

request for that group within the forced-leave interval, the switch then blocks any further group "X"

traffic to the port.

Fast learn

The fast learn option allows fast convergence of multicast traffic after a topology change.

This command is executed in the global config context.

Example 15 To enable fastlearn on ports 5 and 6

HP Switch(config)# igmp fastlearn 5-6

Unjoined multicast traffic

This feature adds a global IGMP multicast configuration option to the switch that results in each

VLAN having a multicast filter. The filter prevents unjoined multicast traffic from being forwarded

on interfaces associated with IGMP queriers. Each filter only contains interfaces that are queriers

on the same VLAN, so multicast traffic is only flooded on interfaces that contain queriers that are

on the same VLAN as the multicast traffic.

On switch bootup, all VLANs that are IGMP-enabled are guaranteed one multicast filter. You can

always reboot the switch to recreate this configuration where each IGMP-enabled VLAN has a

multicast filter.

NOTE: Joined multicast traffic continues to be forwarded as usual.

You must reboot the switch after configuring the per-VLAN filter.

Example 16 Enabling the IGMP multicast filter

HP Switch(config)# igmp filter-unknown-mcast

Command will take effect after saving configuration and reboot.

The following example shows the multicast traffic being flooded to all queriers on all VLANs; this

is the default behavior. The igmp filter-unknown-mcast command has not been executed.

Table 2 Multicast filter table on distribution switch

Member PortsVLAN ID

1, 2, 30 (all VLANs)

How IGMP operates 29