Spanning tree between C4506 & Nortel bay stack 425

Unanswered Question
Jul 23rd, 2008

We have 2 core switches 4506 & 4510R, access switches are nortel bay stack 425. Now we are going to connect all Nortel switches to 2 core switches thru 2 uplinks. We have multiple vlans and load balancing between the 2 Cores.

Kinldy suggest me the best spanning tree protocol which will support these two vendors.

I have this problem too.
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Giuseppe Larosa Thu, 07/24/2008 - 01:56

Verify if the nortel bay stack 425 support 802.1s MST that is the best choice for this scenario.

Hope to help

Giuseppe

pradeepkum Thu, 07/24/2008 - 02:32

I am not much familiar with MST. Is PVST+ work in this scenerio? Also when i config the spanning tree mode in 4506 it is giving me 3 options 1) PVST 2) MST 3) Rapid PVST.

It doesn't shows me PVST+

How to enable PVST+ in 4506? I hope PVST+ will be supported by Nortel bay stack 425.

Giuseppe Larosa Thu, 07/24/2008 - 03:11

Hello,

PVST+ is Cisco proprietary.

It can fall back to the original 802.1D CST (Common Spanning Tree) but this means that from the nortel devices you will see a single STP instance with a single root bridge for all the possible vlans.

For this reason I was suggesting the 802.1s standard.

pvst+ is enabled by default.

spanning-tree mode is the command to define the STP type you use on the switch.

Use the following link as a reference

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_44_se/configuration/guide/swstp.html

hope to help

Giuseppe

Francois Tallet Thu, 07/24/2008 - 09:01

I agree with Giuseppe, it's best to run MST in that case. If you run any pvst flavor (just forget about the + in pvst+, all our switches are pvst+ nowadays), the cisco devices will not see the third party switch. You will be able to do load balancing but:

- except for vlan 1, all the blocked port will be on the 4500

- convergence will be slow in case of failure.

- you could even have short transient loops when links come up.

If you run MST on the 4500s, the blocked port will be on the access switch. You will never have transient loop.

If the third party bridge is capable of running RSTP, you will have fast convergence.

If the third party bridge is capable of running MST in the same region as the 4500, you will be able to achieve fast convergence and load balancing on the uplinks.

Regards,

Francois

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