7600 and IGMP

[rico.nego]

Last time I had a problem with performance on the router 7600 in our external network segment. On the one customer link there were a lot of multicast traffic and my router was broke down. It means that our BGP and

OSPF session were destroyed. When I looked for any reason in the syslog I found information something like this.

%MCAST-SP-6-IGMP_PKT_DROPPED: IGMP: IGMP Queue full (high packet rate/CPU busy), dropped 283112 packet(s) in last 5 minutes.

I don't why because I don't have enabled IGMP on the interfaces or multicast routing. Could you explain why

my router didn't drop this packet in ASIC but sent to the SP. What can I do to block this traffic in the future.

Thanks in advance!

Rico Nego

[Laurent Aubert]

Hi Rico,

IGMP snooping is enabled by default so the 7600 is processing IGMP packets when it's acting like a switch.

You can use Hw rate-limiter to mitigate this:

http://www.cisco.com/en/US/docs/routers/7600/ios/12.2SR/configuration/guide/dos.html#wp1141067

Look at the multicast IPv4 rate-limiter.

[rico.nego]

Hi Laaubert,

Thanks for your answer. Let me ask additional questions. If I disable in the global configuration by no igmp snooping I will not need to use rate-limiter to mitigate this problem. Is it true or not.

( I ask because in this router I don't expect multicast traffic at all).

Regards,

[Laurent Aubert · Accepted solution]

Hi Rico,

If you disable IGMP snooping, the switch will not analyze IGMP packet and multicast traffic will be handled like broadcast.

Be careful because this message is informational only and may not be the root cause of your high CPU issue but only a consequence (CPU busy to process IGMP packets so they are dropped).

If you really don't expect multicast traffic, you can filter it at the edge via ACL or L2 feature like storm control.

Thanks

Laurent.