[c-nsp] excessive buffer overrun/ignored packets on GEIP+ interface

[Carlos Kamtha]

On Sat, Dec 23, 2006 at 08:12:13PM -0600, Anton Kapela wrote:
>  
> 
> > 7507 w/GEIP+ --------> Cat6509 (MM fibre)
> 
> First, we need more info about your config. I can guess what vip you
> have on the geip+, but let us know. Also, cef or dcef? Tell us what
> other hardware you're running, i.e. provide info on the types of pa,
> vip, and int processors in your router.

the geip+ is the vip. it's a full board card. no PAs.

im using cef. 

other slots are vip2-50s with and assormetn of FE-PAs and a DS3 PA. 

> 
> > I have plenty of headroom on the link, so it isnt a BW 
> > availability problem. 
> > 
> > Anyone have any clues as to what's causing this? 
> 
> Often this is how rx-side buffering manifests in dcef mode. On an
> example router here, vip 4 holds a pa-fe-tx and a pa-t3. Vip 4's
> accumulator will hold packets in buffer whenever the final output pa &
> vip that a packet is destined for has no free memd buffer space
> available. Example:
> 
> #sh controllers vip 4 accumulator
> 
> [snip]
> Serial1/0/0:21:
>  MEMD txacc 0x0122: 2065268 in, 10958 drops (0 paks, 0/113/375 bufs)
> 1536kbps
>    No MEMD acc: 2065268 in
>       Limit drops  : 10958 normal pak drops, 0 high prec pak drops
>       Buffer drops : 0 normal pak drops, 0 high prec pak drops
> 
> Checking the int, we see:
> 
>   Last clearing of "show interface" counters 15w5d
>   Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops:
> 41463
>   Queueing strategy: VIP-based fair queuing
>   5 minute input rate 0 bits/sec, 0 packets/sec
>   5 minute output rate 0 bits/sec, 0 packets/sec
> 
> ..so, this is expected. Total pa/vip output drops exceed the rx-side vip
> accumulator drops, i.e. ~40k egress drops and ~10k ingress drops;
> downloadin' fools with bittorrent, perhaps. 
> 
> Now, the ds3/pa-tx:
> 
> FastEthernet4/0/0:
>  local txacc 0x1A0A: 650 in, 0 drops (0 paks, 0/24414/24414 bufs)
> 100000kbps
> Serial4/1/0:
>  local txacc 0x1A12: 5604 in, 0 drops (0 paks, 0/10793/10793 bufs)
> 44210kbps
> 
> ..as we expect, no input drops on are shown, but we can see at least one
> t1 on vip 1 had enough output queue abuse to have rx size drops in the
> input vip. We don't see any pa-level input drops or overruns, so this
> means our vip was able to throw away packets fast enough, otherwise the
> pa would be causing the drops.
> 
> Without more info on your setup it's hard to get very specific, but it
> could be a sign that your vip cannot rx discard fast enough and at
> times, the geip+ pa is doing so instead. Also possible that your cat6 is
> spewing non-cef-switchable packets at your router at a high rate thus
> being discarded. Check the #sh cef not-cef-switched statistics, see if
> these counters correlate with your input discards at all. 


The interface is quiet at the moment. 
MEMD txacc 0x1ACA: 0 in, 0 drops (0 paks, 0/162760/162760 bufs) 1000000kbps
   No MEMD acc: 0 in
      Limit drops  : 0 normal pak drops, 0 high prec pak drops
      Buffer drops : 0 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



> 
> Finally, read over these urls:
> 
> http://www.cisco.com/en/US/products/hw/modules/ps3088/products_tech_note
> 09186a0080094345.shtml
> 
> http://www.frameip.com/dos-cisco/queue_drops.pdf
> 
> -Tk

Sweet thanks i'll have a look.