Allied Telesis AR400 manual IGMP proxy, Example, Page 21 AlliedWare OS How To Note IGMP

IGMP proxy > Example

IGMP proxy

In very simple tree-design networks, IGMP Proxy is a useful simple alternative to a multicast routing protocol for multicasting between VLANs.

An IGMP Proxy sends IGMP Membership Report and Leave group messages to an upstream subnetwork on behalf of downstream devices, and sends Queries downstream. In other words, an IGMP Proxy effectively ferries IGMP messages from one VLAN to another. The IGMP Proxy looks like an IGMP Querier to the downstream VLAN, and like a client to the upstream VLAN. Note that the Proxy can only have one configured upstream VLAN.

IGMP Proxy is available on all Allied Telesis routers and managed layer 3 switches except AT-9800 and SwitchBlade series. For AT-8948, AT-9900 and x900-48 series switches, it requires software version 2.8.1 or later.

If you use IGMP Proxy on a switch, multicast data packets are processed by the CPU so are not forwarded at wirespeed.

Example

IGMP Proxy only works in tree networks, so for this example we convert the network from a loop into a tree by disabling port 50 on the AT-8948 switch.

Switch 3 is the IGMP Proxy. Switch 1 is upstream of the Proxy. Switch 2 is downstream of the Proxy on vlan100. Therefore, the multicast server and client 1 are now in different VLANs and switch 3 sits on the boundary between the two VLANs. This network is shown in the following figure.

Multicast Server		port 1	AT-8948	Switch 1:
		vlan200		Querier
			port 49
				upstream
				vlan200
				port 26
Switch 2:	Rapier 24i	port 25	downstream	Rapier 24i	Switch 3:
Snooper			vlan100	port 25	Proxy
	port 2
	Client 1
					igmp-proxy.eps

Page 21 AlliedWare™ OS How To Note: IGMP