igmp helper address

igmp helper address is used when we want to forward igmp join/leave message to another interface by specifying the ip address of the destination where we want to forward this igmp packet to.

In this example, R4 is trying to get the multicast traffic from R1. However, R3 is not a neighbor of R2. Therefore R4 cannot join the group. We need to add the igmp helper to forward this igmp join request to R2.

R2

interface FastEthernet0/1
 ip address 192.168.2.1 255.255.255.0
 ip pim sparse-dense-mode
 ip pim neighbor-filter 1
 duplex auto
 speed auto

R3

interface FastEthernet0/0

 ip address 192.168.2.2 255.255.255.0

 ip pim sparse-dense-mode

 ip igmp helper-address 192.168.2.1

 duplex auto

 speed auto

end

R4

interface FastEthernet0/0

 ip address 192.168.3.2 255.255.255.0

 ip igmp join-group 239.0.0.1

 duplex auto

 speed auto

Verify configuration

R1#ping 239.0.0.1

Type escape sequence to abort.

Sending 1, 100-byte ICMP Echos to 239.0.0.1, timeout is 2 seconds:

Reply to request 0 from 192.168.3.2, 132 ms