Multicasting And Multicast Services Overview; Understanding How Igmp Snooping Works - Cisco WS-C6506 Software Manual

Understanding How Multicasting Works
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Multicasting and Multicast Services Overview

IGMP snooping manages the multicast traffic in the switches by allowing the directed switching of the
IP multicast traffic. GMRP is protocol independent and can manage both IP multicast traffic and any
Layer 2 multicast traffic.
The switches can use IGMP snooping or GMRP to configure the switch ports dynamically so that the IP
multicast traffic is forwarded only to those ports that are associated with the IP multicast hosts. The
IGMP software components run on both the Cisco router and the switch.
Note For more information on IP multicast and IGMP, refer to RFC 1112. GMRP is described in IEEE 802.1p.
You can statically configure the multicast groups by entering the set cam static command. The multicast
groups that are learned through IGMP snooping are dynamic. If you specify group membership for a
multicast group address, your static setting supersedes any automatic manipulation by IGMP snooping
or GMRP. The multicast group membership lists can consist of both user-defined settings and settings
that are learned through IGMP snooping or GMRP.

Understanding How IGMP Snooping Works

You cannot enable IGMP snooping on a switch if GMRP is already enabled on the switch.
Note
You can run IGMP snooping on any Catalyst 6500 series supervisor engine model (Supervisor Engine 1,
Note
Supervisor Engine 1A, Supervisor Engine 2, Supervisor Engine 720, and Supervisor Engine 32). A PFC
is not required to enable IGMP snooping. Cisco Group Management Protocol (CGMP) is not supported
on the Catalyst 6500 series switches, although the CGMP server is supported on the MSFC. To support
the CGMP client devices, configure the MSFC as a CGMP server.
IGMP version 3 snooping is not supported on the systems with a Supervisor Engine 1 or Supervisor
Note
Engine 1A.
IGMP snooping manages the multicast traffic at Layer 2 on the Catalyst 6500 series switches by
allowing the directed switching of the IP multicast traffic.
The switches can use IGMP snooping to configure the Layer 2 interfaces dynamically so that the IP
multicast traffic is forwarded only to those interfaces that have expressed interest in particular IP
multicast traffic streams through the IGMP join and report messages.
Catalyst 6500 series switches can distinguish the IGMP control traffic from the multicast data traffic. When
you enable IGMP on the switch, the IGMP control traffic is redirected to the CPU for further processing. This
process is performed in the hardware by the specialized ASICs. The ASICs allow the switch to snoop the
IGMP control traffic with no performance penalty.
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
51-2
Redundancy for Multicast Traffic, page 51-9
Chapter 51 Configuring Multicast Services
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