Cisco Group Management Protocol

With the Cisco Group Management Protocol (CGMP) page, you can:

CGMP reduces the unnecessary flooding of IP multicast packets by limiting the transmission of these packets to groups of CGMP clients that request them. These clients (end stations) automatically join and leave groups that receive IP multicast traffic, and the switch dynamically changes its forwarding behavior according to these requests.

CGMP works with the Internet Group Management Protocol (IGMP) and requires a connection to a router running CGMP and IGMP. When the router receives an IGMP request (leave or join) from a client, it forwards this information to the switch in a CGMP packet. The switch uses this information to alter its forwarding behavior.

Disabling CGMP

To disable CGMP (enabled by default):

  1. Deselect the Enable CGMP checkbox.
  2. Click Apply.

Enabling the CGMP Fast Leave Feature

Normally, a CGMP-enabled router does not remove a CGMP group until all members are removed from the group. The CGMP Fast Leave feature reduces the delay by searching for other members of the group on the segment. If there are no other members on the port, the switch removes the port from the group. If there are no other ports in the group, the switch notifies the routers connected to the VLAN to delete the entire group.

To enable the CGMP Fast Leave feature (disabled by default):

  1. Select the Enable CGMP Fast Leave checkbox.
  2. Click Apply.

Note: The CGMP Fast Leave feature is functional only if CGMP is enabled. The client must be running IGMP Version 2 for the CGMP Fast Leave feature to properly function.

Modifying the Router Hold-Time

The router hold-time is the number of seconds the switch waits before removing (aging) a router entry. If the aged router is the last router entry on a VLAN, then all groups on that VLAN are removed.

To modify the router hold-time setting:

  1. In the Router Hold-Time field, enter a number from 10 and 6000.
    The default is 300 seconds.
  2. Click Apply.

Removing Multicast Groups

If the CGMP Fast Leave feature is disabled, you can speed the removal of switch ports (and their end stations) listening to a specific multicast group address through the Current Multicast Groups Table. The table lists the VLAN ID, the IGMP MAC address, and the switch ports listening to this multicast address.

To remove a multicast group:

  1. In the Current Multicast Groups Table, select the IGMP MAC address and port members that you want to remove.
  2. Click Remove.

Note: You can remove all multicast groups by clicking Remove All.

Removing Router Ports

Another way to speed the removal of multicast groups is through the Current Router Ports Table. This table lists the VLAN ID, the IGMP MAC address of the router port, the router age time, and the router port number.

When the router age time shown in the table reaches 0 seconds, and if the router is the last member of the VLAN, the multicast group table is cleared.

To remove a CGMP-enabled router and all the members associated with its multicast group:

  1. In the Current Router Ports Table, select the router and ports you want to remove.
  2. Click Remove.

Note: You can remove all entries in the table by clicking Remove All.