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Cisco 3COM spanning Tree

Posted on 2013-07-01
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Last Modified: 2013-07-29
Hi,

I have the following

2 X 3com 4800 acting as the root of the network.
Various 3com and Cisco switches including a 6500.

To begin with both are set at defaults so the 3coms are running MSTP and the cisco are running common STP. On the 6500 while it is running RSTP (as default) it works OK unless I try to create a port-channel between the CISCO and 3com at which point it falls over.

SO I thought I would change the STP mode on the 6500 to MSTP, but now I get the following error message and the port gets blocked.

SPANTREE-2-PVSTSIM_FAIL: Blocking root port Gi2/1: Inconsitent inferior PVST BPDU received on VLAN 10, claiming root 32778:b4e9.b04c.8100

Can any one tell me what might be causing this issue? the 3com root bridges have both the "root primary and root secondary" command configured and all switches have all vlans added to instance 0 of MSTP.

I would like to get the STP consistence so that I can start migrating all the old 3com to the new 6500 with out worrying about STP issues. Does any one have some suggestions for best practices for 3com / cisco STP interopteribility.

Thank you
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Question by:Aaron Street
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Zephyr ICT earned 500 total points
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Setting MSTP on the Cisco's is a good step, and mapping the VLANs to instance 0 is ok to... But the revision and instance name need to match to if you want switches to be in the same region.

If any one of these don’t match the switches are in different regions and they'll run RSTP.

Maybe you've checked all this, but that's the first thing I thought of...
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by:Aaron Street
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umm of course I have.....

OK its been a while since i set up MSTP and I might have forgotten the revision number...

Thanks I will go check and come back :)
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by:Aaron Street
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I could not get this to work, to be honest looking at the 3COM configuration and non of there Spanning tree is set different to defaults and the new Cisco devices will not join in nicely. Still getting BPDUs from the other cisco devices and putting ports in to errodisable.

I have now enabled rapid PVST on the cisco and left the MST on the 3COM, this seems to work OK but have to test with some loops and see how it gets handled.

Sadly I don't have any test kit to play with so having to do this on a live network. The cisco devices are not in service but the main 3COM is so I don't want to do any thing that might break that.
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by:Aaron Street
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Thank you
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