[c-nsp] Output drops on same ASIC on ME3400 and Cat2970

[Christian Bering]

Hi all,

I have a couple of switches that show the same amount of output drops on
four consequtive ports.

On an ME3400 I am seeing the same amount of output drops (45,949
discards so far today) on ports gig0/9 through gig0/12.

On a Cat2970 I am seeing the same amount of output drops (167,699
discards so far today) on ports gig0/1 through gig0/4.

These two switches have a trunk port between them on gig0/11 on the
ME3400 and gig0/3 on the Cat2970.

I find this odd enough in itself but what makes it even odder is that
the (in total 8) ports are configured very differently. Some are VLAN
trunks, some are access ports, and one port is even a dot1q-tunnel.

The drops do not seem to be related to traffic levels; some of the ports
are at less than 1 kbps utilised.

As far as I understand the architecture of both platforms, ports are
grouped together in 4 on each ASIC.

What could possibly explain why four ports on the same ASIC show the
same amount of output drops?

I can add that I saw the same behaviour on a Cat3560 last week (again
four ports on the same ASIC showing same amount of drops) but after
removing UDLD from one of the ports (copper), the drops stopped. On the
ME3400 and the Cat2970, UDLD is not running on the ports in question.

Thanks in advance,

-- 
Regards
 Christian Bering
 IP engineer, nianet a/s
 Phone: (+45) 7020 8730