Web Management Guide

Table Of Contents
Chapter 13
| Multicast Filtering
Layer 3 IGMP (Query used with Multicast Routing)
– 471
Note:
Multicast Routing Discovery (MRD) is used to discover which interfaces are
attached to multicast routers. (For a description of this protocol, see “Multicast
Router Discoveryon page 445.)
IGMP Proxy – A device can learn about the multicast service requirements of hosts
attached to its downstream interfaces, proxy this group membership information
to the upstream router, and forward multicast packets based on that information.
Configuring IGMP
Proxy Routing
Use the Multicast > IGMP > Proxy page to configure IGMP Proxy Routing.
In simple network topologies, it is sufficient for a device to learn multicast
requirements from its downstream interfaces and proxy this group membership
information to the upstream router. Multicast packets can then be forwarded
downstream based solely upon that information. This mechanism, known as IGMP
proxy routing, enables the system to issue IGMP host messages on behalf of hosts
that the system has discovered through standard IGMP interfaces.
Figure 301: IGMP Proxy Routing
Using IGMP proxy routing to forward multicast traffic on edge switches greatly
reduces the processing load on those devices by not having to run more
complicated multicast routing protocols such as PIM. It also makes the proxy
devices independent of the multicast routing protocols used by core routers.
IGMP proxy routing uses a tree topology, where the root of the tree is connected to
a complete multicast infrastructure (with the upstream interface connected to the
Internet as shown in the figure above). In such a simple topology, it is sufficient to
Layer3 Switch/Router
Router
PC PC
192.168.1.2
192.168.1.3
192.168.2.1 192.168.3.1 192.168.4.1
PC
PC
PC
Upstream
Interface
IP IGMP Proxy
To Internet
Downstream
Interfaces