Cisco IGMP Filtering

Cisco IGMP Filtering

IGMP report messages include the group addresses of the multicast receivers want to join. IGMP enabled routers can filter the groups based on the information in the report messages.

For example lets permit only for the groups in the 224.10.10.0/24 range.

In this scenario, we have two routers(R2 and R3) and a client.R1 simulates the client.These three routers are connected through a Layer2 switch.

R1:

interface FastEthernet0/0

 ip address 192.168.123.1 255.255.255.0

R2

access-list 1 permit 224.10.10.0 0.0.0.255

interface FastEthernet0/0

 ip address 192.168.123.2 255.255.255.0

 ip igmp access-group 1

 ip pim sparse-mode

R3

access-list 1 permit 224.10.10.0 0.0.0.255

interface FastEthernet0/0

 ip address 192.168.123.3 255.255.255.0

 ip igmp access-group 1

 ip pim sparse-mode

We added “ip igmp-join group 224.10.10.1” and “ip igmp-join group 224.1.1.1”  on R1:

R2#debug ip igmp

IGMP debugging is on

*Mar  1 01:02:11.087: IGMP(0): Received v2 Report on FastEthernet0/0 from 192.168.123.1 for 224.10.10.1

*Mar  1 01:02:11.091: IGMP(0): Received Group record for group 224.10.10.1, mode 2 from 192.168.123.1 for 0 sources

*Mar  1 01:02:11.091: IGMP(0): Updating EXCLUDE group timer for 224.10.10.1

*Mar  1 01:02:11.091: IGMP(0): MRT Add/Update FastEthernet0/0 for (*,224.10.10.1) by 0

*Mar  1 01:02:11.659: IGMP(0): Received v2 Report on FastEthernet0/0 from 192.168.123.1 for 224.1.1.1

*Mar  1 01:02:11.659: IGMP(*): Group 224.1.1.1 access denied on FastEthernet0/0

We see that 224.1.1.1 is denied by the multicast routers:

R2# show ip igmp membership

Flags: A  - aggregate, T - tracked

       L  - Local, S - static, V - virtual, R - Reported through v3

       I - v3lite, U - Urd, M - SSM (S,G) channel

       1,2,3 - The version of IGMP the group is in

Channel/Group-Flags:

       / - Filtering entry (Exclude mode (S,G), Include mode (*,G))

Reporter:

       <mac-or-ip-address> - last reporter if group is not explicitly tracked

       <n>/<m>      - <n> reporter in include mode, <m> reporter in exclude

 Channel/Group                  Reporter        Uptime   Exp.  Flags  Interface

 *,224.10.10.1                  192.168.123.1   00:08:08 02:12 2A     Fa0/0

 *,224.0.1.40                   192.168.24.4    00:56:13 02:16 2A     Fa1/0

 *,224.0.1.40                   192.168.123.2   01:04:35 stop  2LA    Fa0/0