[c-nsp] 3750 Dropping into software forwarding?

[Will Hargrave]

Peter Kranz wrote:
> Had one of our customer's 3750's jump in CPU utilization from its normal 18%
> or so to 80%, and the amount of traffic it would forward drop to around 100
> Mb/s via one of its BGP peers. I tried dropping a few routes from the peer
> and suddenly CPU utilization dropped back to 18% and all's well. This box
> has about ~3500 routes on it. No errors showed up in the logs. Running Cisco
> IOS Software, C3750 Software (C3750-I5-M), Version 12.2(25)SEA, RELEASE
> SOFTWARE (fc)

Have a look at 'show sdm prefer'? The info on limits is here:

http://www.cisco.com/en/US/products/hw/switches/ps5023/products_configuration_guide_chapter09186a00803947e5.html

> I noticed this in the CEF memory, and I'm guessing I've hit a memory limit
> in CEF causing it to dump back into software forwarding. Will another SDM
> profile help this situation, I'm currently in "desktop default".

Your available tcam also depends on what model switch you're running -
the 12SFP model has more TCAM available.

By my reading of that table, your template only supports 2k 'indirect'
(i.e. not directly connected) routes. You need to change your SDM
template, this will require a reload.

I don't think the info you pasted (show cef memory) is particularly
relevant to the problem at hand, I suspect that's software CEF table,
and your problem is with TCAM.

It's a shame that Cisco don't give any guidance on how to interpret
'show platform tcam usage' on 3750. On 6500 you can do 'show platform
hardware capacity forwarding' to check your TCAM usage.

I guess I could file an enhancement request since I have a bunch of
3750s on smartnet, but I don't know how much these kind of requests are
listened to in Cisco and whether anyone would actually give a shit :-)

Will