[c-nsp] 3560 mtu miss-match causing output drops

[Peter Rathlev]

On Sat, 2010-03-13 at 10:27 +1000, mb at adv.gcomm.com.au wrote:
> Have a 3560G running system mtu of 1998, with one port recently 
> connected to new service provider that is reporting output 
> drops(Traffic only hitting 50-60Mb) - Provider has stated that there 
> connecting equipment only supports mtu of 1540, and as 3560's do not 
> support per-int mtu, only option is to change system mtu, which I
> would prefer not to do.

Drops on account of MTU wouldn't show up as errors in your end. Only way
to see them was to look for "giant frames" on the other end.

If your drop counter increases you have to look at why. Look at "show
interface Gi0/X counters errors". If they're OutDiscards, look at "show
platform port-asic stats drop Gi0/X". Maybe adjust the QoS model. (Even
with QoS disabled it uses queueing.)

If the ISP link is 100 Mbps, the other links are 1 Gbps and traffic is
primarily in their direction you might've run into the much
discussed-about buffering on the 3560 platform.

-- 
Peter