igmp querier

[kwunchungchan]

Hi all,

In my LAN, two routers are running PIM. There should be 1 IGMP querier and 1 DR.

One of them is DR now. However, both become IGMP querier now.

Any idea?

Thanks a lot!

[ebreniz]

Could you use this document for trouble and find someother behaviours

http://www.cisco.com/en/US/tech/tk828/tk363/technologies_tech_note09186a0080093f21.shtml

[Steve Fuller]

The IGMP Querier election process is slightly different between IGMP v1 and IGMP v2.

In IGMP v1 the election process relies on the L3 multicast routing protocol (DVMRP, PIM etc.), whereas the function is part of IGMPv2. The device elected as querier will depend on the L3 protocol if you're running IGMPv1, but should be the router with the lowest IP address on the LAN segment if you're running IGMPv2.

Are both devices running the same IGMP version?

Also do you have L3 connectivity between both routers on the LAN segment where they are both IGMP querier? A discontiguous subnet could cause this as each router would not know the existance of the other.

Regards

[kwunchungchan]

Thanks for your reply.

The two routers are running IGMPv2 which is enabled automatically when I configure PIM Sparse-Dense mode.

They are in different site and connected on the same LAN which is separated by many switches. I also suspect that they are on discontiguous subnet. However, these two routers can form PIM neighbour. How can I verify it?

The following is the screen dump.

routerA>sh ip igmp int e0

Ethernet0 is up, line protocol is up

Internet address is 10.228.2.8/16

IGMP is enabled on interface

Current IGMP version is 2

CGMP is enabled on interface

IGMP query interval is 60 seconds

IGMP querier timeout is 120 seconds

IGMP max query response time is 10 seconds

Last member query response interval is 1000 ms

Inbound IGMP access group is not set

IGMP activity: 24 joins, 11 leaves

Multicast routing is enabled on interface

Multicast TTL threshold is 0

Multicast designated router (DR) is 10.228.2.8 (this system)

IGMP querying router is 10.228.2.8 (this system)

Multicast groups joined (number of users):

224.0.1.40(1)

routerB>sh ip igmp int fa0/0

FastEthernet0/0 is up, line protocol is up

Internet address is 10.228.2.6/16

IGMP is enabled on interface

Current IGMP host version is 2

Current IGMP router version is 2

CGMP is enabled on interface

IGMP query interval is 60 seconds

IGMP querier timeout is 120 seconds

IGMP max query response time is 10 seconds

Last member query count is 2

Last member query response interval is 1000 ms

Inbound IGMP access group is not set

IGMP activity: 61 joins, 47 leaves

Multicast routing is enabled on interface

Multicast TTL threshold is 0

Multicast designated router (DR) is 10.228.2.8

IGMP querying router is 10.228.2.6 (this system)

Multicast groups joined by this system (number of users):

224.0.1.40(1)

routerB>sh ip pim nei

PIM Neighbor Table

Neighbor Interface Uptime/Expires Ver DR

Address Prio/Mode

10.228.2.8 FastEthernet0/0 2w0d/00:01:40 v2 N / DR

[Steve Fuller]

The captures you've pasted show the routers have formed a PIM neighbor relationship.

Are you able to perform a "debug ip igmp" on both routers? If so do you see IGMP query messages being sent and received from both routers or only from one?

The behaviour would seem to suggest that PIM packets (224.0.0.13) are being seen whereas IGMP General Query packets (224.0.0.1) are being dropped.

Some things that might be worth checking:

1) Does a "sh ip int" on both routers show that both have joined the reserved groups 224.0.0.1 and 224.0.0.13?

2) If you do "ping 224.0.0.1" on each of the routers in turn (when in enable mode) do you see a reply from the other router?

3) Is there any kind of IGMP/CGMP snooping running on the switches in between the two routers that could cause the packets for one address to be dropped?

Regards

[kwunchungchan]

Thanks for your reply!

I can't enable the debug command as the routers are in production.

1) both routers have joined 224.0.0.1 and 224.0.0.13

2) when ping 224.0.0.1, it shows "UUUUU" which means its unreachable

3) IGMP snooping maybe enabled in between, but why only 224.0.0.1 is dropped?