[c-nsp] Stack port flaps on Cisco 3750G series (was: Re: Catalyst 3750 stacks with many members)

[Tristan Gulyas]

Hi,

We've had no real trouble with large stacks of 3750G switches vs. smaller 
ones - I can see we have over 60 stacks of 7 and above (14 of these are 9 
stack members).  We poll these switches every minute using SNMP (statseeker, 
cacti) and have several scripts that perform configuration backups.  I can't 
say I've seen high CPU at all.

Unfortunately one problem we've seen has been related to the stack ports - 
without warning, we will see stack ports flap down/up between paticular 
switches.  In one or two cases, the stack cable has been at fault but 
usually an RMA fixes the problem.  We monitor syslog for this and we have 
scripts that check every switch stack for stack interconnects which are down 
(the danger here is that when a stack link fails, we aren't informed about 
it).  If the stack ports flap up/down rapidly and for a long time in quick 
succession, the stack will crash and reload.  Reproducing this issue in the 
lab has been a challenge and it seems to be environmental - i.e. we notice 
this more on warm, humid days.

Has anybody else encountered this issue?  It doesn't seem at all related to 
the size of the stack, either.

thanks,
Tristan
----- Original Message ----- 
From: "Dale Shaw" <dale.shaw+cisco-nsp at gmail.com>
To: <cisco-nsp at puck.nether.net>
Sent: Saturday, November 15, 2008 5:19 AM
Subject: [c-nsp] Catalyst 3750 stacks with many members


> Hi all,
>
> We have a few large (>6 member) cat3750 stacks in our environment,
> most in L2 edge/access roles, and most providing PoE to cisco IP
> phones.
>
> Does anyone have any tips as to how to make large stacks more
> reliable? We're seeing really high CPU and have found you need to be
> really careful doing anything that has the potential to swamp the CPU
> -- the other day I crashed a stack master by clearing the CDP
> neighbour table (a bit silly in hindsight, given the number of CDP
> table entries [phones], but I was troubleshooting a stale neighbour
> problem).
>
> Does changing to the 'VLANs' SDM template for switch stacks in this
> role make any difference? These stacks don't do any routing, or
> traffic ACLs.
>
> We've tried 12.2(40)SE, 12.2(44)SE2 and 12.2(44)SE3. Our biggest stack
> is 7 members. You're supposed to be able to stack 9 of these things
> (and I don't recall reading about any caveats), so it's a bit
> concerning. Disabling certain functionality (e.g. CDP) to stabilise is
> one thing, but long term it would be nice if it 'just worked'.
>
> cheers,
> Dale
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