RPVST loop issue

Unanswered Question
Jun 16th, 2009


i have cisco 2851 wan router connected to 2 differnt cisco 3560 switches.The 2 on board Gig interfaces are part of BVI interface and ip has been given to BVI interface.Both cisco 3560 swicthes connected to each other on fa0/24.Gi 0/1 of both switches connected to one firewall each downside.ip has been configured with firewall interface.this setup works fine and fiewall able to reach wan router bvi interafce.when we add 2nd wan router with similar setup we get spanning tree problem.

Attachment has all details mentioned.request the expert opinion on the same.

I have this problem too.
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Giuseppe Larosa Tue, 06/16/2009 - 22:41

Hello Sameer,

using the STP show commands like

show spanning-tree vlan 3

show spanning-tree interface type x/y

you need to understand what changes for vlan3 and vlan4.

Is vlan2 the native vlan on the trunks?

Are the router wan2 and wan3 configured with

bridge x protocol ieee ?

Be aware that routers will be able to speak only 802.1D legacy spanning tree so you cannot take advantage of Rapid STP.

Verify that the switches fall back to legacy STP on the interfaces connected to the routers.

the switches should see each other on the direct link between them.

For each vlan see who is claiming to be the root bridge.

If both claim to be root bridge for vlan3 verify if the trunk between is really in trunking state and if the list of permitted vlans include vlan3 on both ends.

Hope to help


sameermunj Tue, 06/16/2009 - 22:58


the problem is resolved.actually the bridge protocol ieee was missing in wan router 2& 3.after adding the same ports on one switch went into blocking mode.


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