3Com Switch 7757, Configuration Manual

Page: 453 / 940

Overview 453
3 switch in the leaf network (Switch B in the figure). The Layer 3 switch will then
forward IGMP join or IGMP leave messages sent by the connected hosts. After the
configuration of IGMP Proxy, the leaf switch is no longer a PIM neighbor but a
host for the external network. Only when the Layer 3 switch has directly
connected members, can it receive the multicast data of corresponding groups.
Figure 111 Diagram for IGMP Proxy
Figure 111 is an IGMP Proxy diagram for a leaf network.
Configure Switch B as follows:
■
Enable multicast routing on VLAN interface 1 and VLAN interface 2, and then
configure the PIM protocol on it. And configure the IGMP protocol on
VLAN-interface 1 at the same time.
■
On VLAN interface 2, configure VLAN interface 1 as the outbound IGMP Proxy
interface to external networks. You must enable the IGMP protocol on the
interface first, and then configure the igmp proxy command.
Configure Switch A as follows:
■
Enable multicast routing and configure the IGMP protocol on VLAN interface 1.
■
Configure the pim neighbor-policy command to filter PIM neighbors in the
network segment 33.33.33.0/24. That is, Switch A does not consider Switch B
as its PIM neighbor.
In this case, when Switch B of leaf network receives from VLAN interface 2 an
IGMP join or IGMP leave message sent by the host, it will change the source
address of the IGMP information to the address of VLAN interface 1: 33.33.33.2
and send the information to VLAN interface 1 of Switch A. For Switch A, this
works as if there is a host directly connected to VLAN interface 1.
Similarly, when Switch B receives the IGMP general group or group-specific query
message from the Layer 3 Switch A, it will also change the source address of the
query message to the IP address of VLAN interface 2: 22.22.22.1 and send the
message from VLAN interface 2.
In Figure 111, VLAN interface 2 of Switch B is called the client and VLAN interface
1 of Switch B is called the proxy.
IGMP report/leave
message
V LA N-int 2
22.22.22.1
V LA N-int 1
33.33.33.1
V LA N-int 1
33.33.33.2
S w itchA
S w itchB
General/group-specific
query
E xterior netw ork
S tub netw ork
H ost
IGMP report / leave message
General /group -specific query