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TTM Network Administration Documentation

Multicast Protocols

Network segment nodes use the IGMP protocol to notify routers of their multicast address subscriptions. Larger and newer switches include ASIC components that can snoop IGMP packets in the hardware. These switches can then generate their own IP multicast forwarding tables.

Examples include:

  • Catalyst 5x00 series with Supervisor III family
  • Catalyst 6x00 series

While IGMP snooping is enabled, switches process IGMP messages internally. However, your network still needs a router to solicit IGMP reports from your network's end-nodes.

In its own networks, TT uses this type of IP multicast forwarding on Catalyst 6500 series switches. Based upon this experience, TT recommends its use.

If you set up IGMP snooping, use IGMP Version 2.0 protocol. For information on Windows’ support of IGMP, refer to the article Q193907 in Microsoft's knowledge base.


TT recommends that you do not use CGMP and does not support its software in such a network environment.

To deploy CGMP on a network, you must connect a router (with IP multicast enabled) to the switch infrastructure. This router processes the multicast IGMP packets to determine subscription groups and the MAC addresses that subscribe to them. The router then periodically floods this information to all switches on the network.

After testing its products in a CGMP environment, TT found this method unreliable for TTM and certain TT Gateway architectures. Additionally, if CGMP incorrectly filters a port, the node that connects through that port frequently disconnects. These interruptions can last up to several minutes.


TT recommends that you do not use GMRP and does not support its software in such a network environment.

GMRP enables nodes to register their multicast subscriptions directly with the switching infrastructure. This method does not need a router with IP multicast forwarding enabled. Instead, the device drivers for all NICs on the network must support GMRP, and you must enable GMRP on those NICs. By default, certain NICs have GMRP disabled.

GMRP is a new protocol and TT has not fully tested IP multicast in this sort of network environment.