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Configuring CGMP
Configuring Static Addresses for EtherChannel Port Groups
Follow these rules if you are configuring a static address to forward to ports in an EtherChannel
port group:
•
•
Configuring CGMP
CGMP reduces the unnecessary flooding of IP multicast packets by limiting the transmission of these
packets to CGMP clients that request them. The Fast Leave feature accelerates the removal of unused
CGMP groups. By default, CGMP is enabled, and the Fast Leave feature is disabled.
End stations issue join messages to become part of a CGMP group and issue leave messages to leave the
group. The membership of these groups is managed by the switch and by connected routers through the
further exchange of CGMP messages.
CGMP groups are maintained on a per-VLAN basis: a multicast IP address packet can be forwarded to
one list of ports in one VLAN and to a different list of ports in another VLAN. When a CGMP group is
added, it is added on a per-VLAN, per-group basis. When a CGMP group is removed, it is only removed
in a given VLAN.
The same multicast MAC addresses cannot belong to both CGMP and Multicast VLAN Registration
Note
(MVR) groups. CGMP does not dynamically learn addresses that are MVR group members. If you want
CGMP to learn an address that is already an MVR group member, remove the address from the MVR
group.
Conversely, you cannot add an address to an MVR group if it is already a CGMP group member. If you
want an address that is already a CGMP group member to be an MVR group member, remove the address
from the CGMP group, and then statically add it to the MVR group. For information about MVR, see
the
Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide
6-20
For default source-based port groups, configure the static address to forward to all ports in the port
group to eliminate lost packets.
For destination-based port groups, configure the address to forward to only one port in the port
group to avoid the transmission of duplicate packets.
"Configuring MVR" section on page
6-27.
Chapter 6
Configuring the System
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