Multimedia Traffic Control with IP Multicast (IGMP)
How IGMP Operates
How IGMP Proxy Forwarding Works
The following steps illustrate how to flood a flow from the PIM-SM domain
into the PIM-DM domain when an IGMP join for that flow occurs in the
PIM-DM domain (refer to figure 2-4).
1. Routing Switch 1 is configured with the IGMP proxy forwarding function
to forward joins towards Border Router 1. Routing Switch 1 is also
configured to forward joins from VLAN 1 toward Border Router 2, as is
VLAN 4 on Routing Switch 3.
2. VLAN 2 on Routing Switch 2 is configured to forward joins toward Border
Router 1.
3. When the host connected in VLAN 1 issues an IGMP join for multicast
address 235.1.1.1, the join is proxied by Routing Switch 1 onto VLAN 2 and
onto VLAN 4. The routing information table in Routing Switch 1 indicates
that the packet to Border Router 1 and Border Router 2 is on VLAN 2 and
VLAN 4, respectively.
2-19
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