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Strange VLAN issue

Strange VLAN issue

Strange VLAN issue


I will try and explain this as best as I can.

We have a core Cisco 4500 DIRECTLY connected to a 5760 WLC via Etherchannels. The etherchannel group is set correctly and has multiple VLANs running across it. We needed to add an extra VLAN, VLAN 400 and added to the port channel which updated the interfaces correctly. The interface on the WLC has also been updated correctly. The VLAN configuration is setup exactly the same as a working one on the WLC. So, let's say we have 2 VLANs in operation, VLAN 300 and VLAN 400.

The following results can be seen with ping tests:

VLAN 300 can ping the Core switch Gateway address for that VLAN.
VLAN 400 - the ping fails when pinging the core switch Gateway address for that VLAN.

The only difference I can see between the two VLAN configs is shown below:

spanning-tree mode rapid-pvst
spanning-tree extend system-id
spanning-tree vlan 132,134,199,201-236,254,301-305,534-599,801 priority 24576
spanning-tree vlan 802-835,999 priority 24576

As can be seen, VLAN 300 is listed in the Spanning Tree but VLAN 400 is not. Could it be that Spanning Tree is seeing a potential loop on VLAN 400 and is closing the VLAN interface? It does not show as shutdown, but these are directly connected devices and they just will not ping each other. Communication on VLAN 400 the other side of the Core is fine and everything works as should. Is there a command that can be used to see if Spanning Tree is doing something unusual on VLAN 400?

If any more information is required then please let me know.


RE: Strange VLAN issue

Again, I have solved the issue and it was indeed Rapid Spanning Tree causing the issue and blocking the VLAN interface.

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