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Connecting 2+ 35XX to 1 400X

I am experiencing severe network performance problems when I connect 3 Cat3524's to 1 Cat4003

(fibre dot1q GBic links).

All in 1 physical loop. The Cat 4003 is the root bridge (connected to router). The bizarre thing is if I disconnect the fibre between the 4003 and the first 3524 (forcing all the traffic the long way round) it all works OK.

Reconnect the fibre and problem reappears. I have replaced the switch, fibre, and GBIC on this first switch and still the problem does not go away.

Is there a compatability issue between 400X and 35XX

I am missing ???


4003 Flash:cat4000.5-5-4b.bin

3524 Flash:c3500XL-c3h2s-mz-120.5.2-XU.bin

3524 Flash:c3500XL-c3h2s-mz-120.5.2-XW.bin

The newer switch which went in has a slighty different revision.

I have tried everything .. 4003 is VTP server rest are clients - Diameter set to 3 on 4003,

The trunk is set to ON on the 4003 so I believe DTP is not an issue.

Any Ideas ??

Community Member

Re: Connecting 2+ 35XX to 1 400X

At least at one time, the 4000 series only supported dot1q trunking and the 3500 series defaulted to ISL. You might want to check to see if there's a mismatch and change the 3500's. I always set trunking on as well.

I don't know whether that explains why it works when you break the loop. Are all the ports on the 3500's in the same VLAN?

Community Member

Re: Connecting 2+ 35XX to 1 400X

Did you check your spanning tree configuration? Sounds like there could be some issues.

Can you post the config's for these switches?


Community Member

Re: Connecting 2+ 35XX to 1 400X

Yeap Spanning tree looks OK, its blocking in the right place, I make the 4000 the root, costs all look OK, When I make a topology change and debug Spantree events, I can see it go through the spanning tree rebuilding stages OK. Usually with spanning tree problems it will keep recalulating the topology but it isnt doing that in this case.

Community Member

Re: Connecting 2+ 35XX to 1 400X

It be any comfort, I am in the midst of a very difficult Support issue with two Cat4006/SupII acting as a core with 3524 edge switches, also connected with GE dot1q trunks. STP like symptoms, but no reconfigs jsut like you. This field notice was a good fit but did not fix our problem :

As you are running 5-5-4b you might want to take a look.

It has not done the trick for me however.

Community Member

Re: Connecting 2+ 35XX to 1 400X

You will actually want to use "nonegotiate" as the trunk mode instead of "on" to connect the Cat4k to the XL series switches.


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