[c-nsp] difference between OutDiscards and Overruns

[Peter Rathlev]

On Thu, 2011-07-21 at 00:17 +0300, Martin T wrote:
> ok, thanks! I see this on Gi port of
> WS-C3750G-24TS-S1U(c3750-ipbasek9-mz.122-44.SE1.bin). Regarding this
> QoS comment- you mean if one experiences this OutDiscards issue on a
> router port, where QoS is applied, then packets with high QoS priority
> will not be dropped as they have higher priority in outbound buffer?

That depends on how it's configured. :-)

The 3750 can tell you what it dropped on a port with "show mls qos
interface GiX/0/Y statistics". If this command doesn't give you any
enqueue/drop statistics you instead need to look at "show platform
port-asic stats drop GiX/0/Y". (Depends of IOS version, e.g. 12.2(35)SE5
doesn't and 12.2(55)SE1 does. Don't know about 12.2(44)SE1.)

To figure out what traffic goes to what queue you can look at the
QoS-maps with "show mls qos maps ...".

So assuming that you mark all important packets in a unique way, and
that you give these packets a queue of its own with ample buffer space,
then they should end up not being dropped as much as other packets.

-- 
Peter