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Community Member

STP between c4500 and Dell Switch

Hi All

I heve a redundant C4500 Core which is connected to Dell PowerConnect5324 Switches. The Dell Switches does support Common Spanning Tree (CST) but not per VLAN STP.

My Problem is now, that I cannot find out how to configure CST on the Cat4500 Switches (IOS Based). Only PVST can be configured. I also tried it using MST with a single Instance, but the Spanning tree was not stable.

What is the Best Practice to connect Switches which supports CST only?

Thanks for any hints, Phil

1 ACCEPTED SOLUTION

Accepted Solutions
VIP Purple

Re: STP between c4500 and Dell Switch

Hello Phil,

have you configured MST with instance 0 ? That instance (0) corresponds to Common Spanning Tree, if you have not tried that yet, you might want to give it a shot...

Regards,

GP

4 REPLIES
Community Member

Re: STP between c4500 and Dell Switch

Hi Phil

I don't know if this helps, but I a while ago I had a need to connect a Cisco-based switched infrastructure to a pair of rednundant F5 BigIP application load-balancers, which only support 802.1d CST.

Now I'm not saying this is the best way of doing it, but it worked for me.

I created a separate link from the Cisco device to the BigIPs for every Vlan.

You can still (I think) create a trunk from Cisco to F5 (or Dell in your case) but if one vlan is blocked by STP on that trunk, then all Vlans will be blocked at the same time.

So you have a choice between using a number of ports rather than one, or having the possibility of the inter-switch link go down completely.

VIP Purple

Re: STP between c4500 and Dell Switch

Hello Phil,

have you configured MST with instance 0 ? That instance (0) corresponds to Common Spanning Tree, if you have not tried that yet, you might want to give it a shot...

Regards,

GP

Re: STP between c4500 and Dell Switch

Hi Phil,

In Cisco's PVST, vlan 1 is the CST. That's where you can configure STP parameters that will interact with the third party bridges. The STP instances running on the other vlans (on the Cisco bridge) use a proprietary BPDU format. These BPDUs are flooded through the third party bridges (these bridges just look like a wire for the Cisco bridge).

The most simple way to have a Cisco bridge running a unique STP instance in the pure IEEE fashion is to run MST (don't create any instance, just use the mst mode). If this is what you were doing, could you be more specific about the instability you had?

Regards,

Francois

Community Member

Re: STP between c4500 and Dell Switch

Thanks to all of you!

I learned a lot in the meentime:

PVST is the mode to use with devices which runs CST only (as Francois explained in detail)

And MST using on Instance gives you an unic STP (also as explained from Francois)

The Instability i had was following:

I had a dublicated Address in my Network, so the Switch debugs told me that a specific Address is seen on different Ports (swapping). I assumed that there is a loop im my Spanning tree, but it wasn't, it was just a Problem with a wrong configured host and my interpretation was wrong.

So I couldn't find any stable STP solution, because the Problem was a different one..

Thanks to all, Phil

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