[c-nsp] 3550 Port Fault that only forwards small packets

[Paul Cosgrove]

Hi Kevin,

Do the switches show high cpu or high throughput on those ports?  If you 
post the interface stats (e.g. show int switching, sh int, sh vlan) 
perhaps it will help.

Are the two limits exactly 500 & 1000? I wasn't clear from your email if 
this was the case or if you were giving an approx range. Is there a very 
clear cut off after 1000 bytes, with no replies at all after that?

If the switch IP and PC were in the same vlan then the only differences 
I can think of are that the extended ping may be sending at a faster 
rate than a windows ping; the frame size is different if you enter 1000 
for each (the frame sent by windows would be 28 bytes larger); and the 
switch may perhaps(?) drop or rate limit locally generated/destined icmp 
before cef switched transit traffic if it is under heavy load.  ICMP is 
not normally considered high priority traffic.

What kind of traffic would you expect on the network, much multicasts or 
broadcasts for instance?

Paul.

Kevin.X.White at corusgroup.com 1wrote:
> 
> We use 3550-FX for fibre distribution and have had a couple of instances
> whe we've been investigating user complaints of a sudden onset of poor
> perfomance and found a port which has no errors of any kind will pass pings
> <500-1000 (btw the failure point is not around 1500) but no larger, also
> telnet sessions would intermittantly stutter if a long output say show tech
> was used.
> 
> On one occasion, after moving the feed onto another port ( all working
> fine) and hanging a 2940 on the faulty port to do some testing I was
> baffled by the fact that an extended ping of 1K from a switch through this
> port would fail but a 1K DOS ping from a PC on the same box I was pinging
> from would succeed!
> 
> The only measurable symptom of the fault is RX drops on the 2950 that was
> connected to the faulty port but I have too many of those to monitor with
> Solarwinds!
> 
> I've now had this on 3 of 3550s along with hard port failures so we are
> moving to 3560s with m/c racks :-(  2 down 10 to go!
> 
> Suggestions or comments welcomed.
> 
> 
> Kevin
> **********************************************************************
> This transmission is confidential and must not be used or disclosed by
> anyone other than the intended recipient. Neither Corus Group Limited nor
> any of its subsidiaries can accept any responsibility for any use or
> misuse of the transmission by anyone.
> 
> For address and company registration details of certain entities
> within the Corus group of companies, please visit
> http://www.corusgroup.com/entities
> 
> **********************************************************************
> 
> _______________________________________________
> cisco-nsp mailing list  cisco-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/cisco-nsp
> archive at http://puck.nether.net/pipermail/cisco-nsp/
> 


-- 
Paul Cosgrove
HEAnet Limited, Ireland's Education and Research Network
1st Floor, 5 George's Dock, IFSC, Dublin 1
Registered in Ireland, no 275301
tel: +353-1-660 9040  fax: +353-1-660 3666
web: http://www.heanet.ie/