Cisco 7613 high cpu observed when bgp peering down.

[Talha Ansari]

I have noticed a very weird behaviour on a cisco 7613 router running with sup720-3b and image 12.2(33)SRD5.

We have bgp peering with the service provider for mpls wan reachability to the remote branches. For some reasons we shutdown the bgp peering from the bgp process with the sp router. Only ping was issued from the Cisco 7613 to the sp router... apart from this there was no traffic on to that port.

We noticed after shuttng down the bgp peer from the bgp process cpu rises to approx 70%. And if we shutdown the physical port the cpu drops to normal 20-30%. There is no other route pointing in the outward direction against that physical port.

Anyone faced such behavior on 7600 or 6500?

When the CPU is high IP INPUT is the process that consumes most of the CPU.

[hbruyere]

Hello!

High cpu in IP Input means that your router is receiving a high load of traffic destinated to itself or requiring software processing (packets with ip options for example).

Here it is a bit weird that this happens when you bring down a BGP peer, so instead of doing some wild guessing about the cause, what you would need to do is to find out what are these packets overloading your CPU.

When you have a high 'IP Input' utilization, look at 'show interfaces'. You'll eventually find one or more interfaces with a loaded input queue (and probably input queue drops too).

Once you have found a suspect interface, repeat the command "show buffer input-interface packet" a few times. This will dump the packets going to software processing. Look at this dump and it will give you good clues about the cause of the problem.

Regards,

Herve

[Talha Ansari]

hi thanks... I will definately check this if I get a chance. As of now the bgp peering is up and production traffic is flowing through that and also the cpu is back to normal on 20-30%. We were not allowed to unshut the port and check as it is one of the core routers.

thanks for your inputs though..

regards.....Talha