CPU Utilization bursts on GSR12008 due to BGP SCANNER

[mpwrdesign]

On a GSR12008 with GRP-B processor, I notice the following.

The CPU utilization of the router usually averages to under 10%. But every 60 seconds to the BGP Scanner running, the CPU utilization runs up to 70%.

This router is a route-reflector for two IBGP clients (receiving 400 routes from each client) and also has an EBGP connection receiving full routes (155000).

Is there a work around or a fix in later IOS versions to reduce these per minute spikes? The GSR is running IOS 120-27.S4

Is this something to be concerned about?

[Georg Pauwen]

Hello,

this is normal BGP behaviour, the BGP scanner process runs every 60 seconds to confirm reachability of the next hops. If you have the full Internet routing table, this will put a heavy load on your CPU. Since you have the GSR12008, I assume you work for an ISP ? If at all possible, you might want to try and reduce the BGP table, which might not be an option for an ISP...

Check the following document:

Troubleshooting High CPU Caused by the BGP Scanner or BGP Router Process

http://www.cisco.com/warp/public/459/highcpu-bgp.html

HTH,

GP

[mpwrdesign]

Thank you GP.

I was concerned about the spikes going up to 70 - 75%.

Yes, this is an ISP router, and at the most, I can reduce about 5-10% of routes from the full routing table being received from my upstream BGP peer.

[Harold Ritter]

As Georg stated, this CPU spike is due to next-hop validation and should not be too much of a concern on a distributed platform like the GSR since this process runs at lower priority and the RP should not be involved with forwarding packets.

The next-hop validation has been replaced by Next-hop tracking (NHT) in 12.0(29)S, which dinamically tracks the status of the BGP next-hops and therefore gets rid of this CPU spike every 60 seconds (or whatever the BGP scan-time might be set to).

Please refer to the following URL for more information on BGP NHT:

http://www.cisco.com/en/US/partner/products/sw/iosswrel/ps1829/products_feature_guide09186a00802a6fad.html

Hope this helps,

[gewhite]

Can you enable bgp dampening... If so, this may take away some of the CPU headaches that BGP Scanner is giving you...

[mpwrdesign]

I will give it a try and see if it alleviates the problem.

Thank you.