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3750 Problem (hard one)

Hi, I have intermitant problems with 3750 switch. Cisco TAC has not been able to find the problem. 1 CCIE consultant tried but failed also.

Problem Symptoms:

1.intermitant loss of voice quality on IPphone(7911 and 7940).

2.STP TC comming FROM stackport(The root change for 1 second causing network and voice outage).

Network Topology

4 3750G-12S (L2 aggregation and STP root)

12 wiring closet with anywhere from 1 to 8 stackets 3750 switch.

2 wiring closet made with legacy 3500XL (will be replace in the next few weeks)

Link between L2aggregation and wiring closet are all cross-stack etherchannel

(2 link with 1 blocking for 3500XL)

STP mode is PVST+ , vlan can span multiple wiring closet.

What was done...

Replaced all switch,cable,gbic

QOS configuration is perfect(validated by TAC and our SE)

There is no link flapping

debug output show one switch(never the same) in the wiring closet stack declare itself the STP root.

Conclusion...need fresh idea on this


Re: 3750 Problem (hard one)

If there is no link flapping, the only way a switch can declare itself to be root is by aging out the information it receives. With STP and no timer tuning, it's a matter of not receiving a BPDU for 20 seconds (max-age), a *very* long time (unless you have a huge network diameter, which does not seems to be the case).

Could you forward more information on the troubleshooting already performed? Is the problem only occurring in a stack?



Re: 3750 Problem (hard one)

The diameter is small (3). There is 25 vlans active in this building.

I'm migrating to 3750 switch from a 3500Xl based network and rolling out IPtelephony at the same time. I've got 4 building done out of 35. 2 small (no problem there) and 2 with more than 1000 host. I'm having problem in the 2 biggest deployment. One of those is housing high management(bad thing).

Case 605483191 should be closed by now. It was going nowhere.

Our Cisco SE is also working on this issue and has not find anything.

I'm adding a show tech...with addressing info removed.