Product guide

Multimedia Traffic Control with IP Multicast (IGMP)
How IGMP Operates
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.
Routing Switch
2
Routing Switch 3
Border
router 1
PIM DM DOMAIN
VLAN 3
V
LA
N
4
Proxy joins
towards Border
router 1
Border
router 2
Routing Switch 1
VLAN 1
VLAN 2
Initial IGMP
join
For 235.1.1.1
V
L
A
N
5
Proxy joins towards Border router 2
PIM SM DOMAIN
Multicast traffic source
(Multicast address
235.1.1.1
Figure 2-4. IGMP Proxy Example
2-19