Chapter 14
| Multicast Filtering
Layer 3 IGMP (Query used with Multicast Routing)
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multicast traffic. Layer 3 IGMP Query, as described below, is used in conjunction
with both Layer 2 IGMP Snooping and multicast routing.
IGMP – This protocol includes a form of multicast query specifically designed to
work with multicast routing. A router periodically asks its hosts if they want to
receive multicast traffic. It then propagates service requests on to any upstream
multicast router to ensure that it will continue to receive the multicast service. IGMP
can be enabled for individual VLAN interfaces (page 578).
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 Discovery” on page 550.)
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 365: IGMP Proxy Routing
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 IGMPProxy
To Internet
Downstream
Interfaces
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