[c-nsp] FE ignored errors

[Jon Lewis]

On Mon, 20 Dec 2004, Gert Doering wrote:

> Cisco/fe6/0/0 [20.12. 1324-1329]: +128 input errors
> Cisco/fe6/0/0 [20.12. 1334-1339]: +64 input errors
> Cisco/fe6/0/0 [20.12. 1354-1359]: +154701 input errors
> Cisco/fe6/0/0 [20.12. 1419-1424]: +243 input errors

This is pretty similar to what we're seeing.  Do you know if there was any
network event that coincided with the 154701 errors...perhaps a BGP flap
on one of your transits?  I can make our other internet transit interfaces
get tens of thousands of FE input ignored errors by flapping a transit BGP
session on another router...even when our aggregate traffic is quite low
(30-40mbit/s spread across 2 transit FE's on separate 7500s 4am this
morning).

Do you worry that you may be providing impaired service when you have a
burst of 100k+ input errors?

> > show control vip N accum confirms this.  We're dropping packets because
> > the VIPs can't get buffers on the RSP MEMD, and at times are failing to RX
> > buffer.
>
> I'm not sure how to read the output of this command.

This page documents how to read the output.
http://cio.cisco.com/en/US/products/hw/modules/ps3088/products_tech_note09186a0080094345.shtml

> show vip accumulator from Slot 6:
> Buffered RX packets by accumulator:
>  Forward queue 0 : 446522 in, 2578 drops (0 paks, 0/24414/24414 bufs) 100000kbps
>    No MEMD buf: 446522 in
>       Limit drops  : 0 normal pak drops, 0 high prec pak drops
>       Buffer drops : 2578 normal pak drops, 0 high prec pak drops
>  Forward queue 8 : 29321 in, 0 drops (0 paks, 0/37841/37841 bufs) 155000kbps
>    No MEMD buf: 29321 in
>       Limit drops  : 0 normal pak drops, 0 high prec pak drops
>       Buffer drops : 0 normal pak drops, 0 high prec pak drops

hmm...your output is a bit different...probably because you're running
12.0S and I'm running 12.2S.

here's part of the output looking at a transit interface's input...this
output interface is a T3 that connects the transit router to part of our
backbone.

Serial4/1/0:
 MEMD txacc 0x1A8A: 4853423 in, 7361306 drops (0 paks, 0/10793/10793 bufs)
44210kbps
   No MEMD acc: 4853423 in
      Limit drops  : 6339503 normal pak drops, 0 high prec pak drops
      Buffer drops : 1021803 normal pak drops, 0 high prec pak drops
   No MEMD buf: 0 in
      Limit drops  : 0 normal pak drops, 0 high prec pak drops
      Buffer drops : 0 normal pak drops, 0 high prec pak drops

This shows a whole bunch of packets got dropped because there were no MEMD
buffers and the VIP had no more room for RX buffering.

> We do (1000 in, 500 out), but I'm not sure it made any difference - it's
> hard to measure, as the effects *are* highly sporadic.

If you're still seeing occasional bursts of 100k+ ignores, it doesn't
sound like it's helped much.

----------------------------------------------------------------------
 Jon Lewis                   |  I route
 Senior Network Engineer     |  therefore you are
 Atlantic Net                |
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