Trunk Link Problem with PVST / SPANNING TREE 1

[matt054]

I have a small network with 4 access level switches and a core switch . These are in a star topology with the core in the centre and each switch connected to the core via a single Gig trunk Ethernet link. On the 3560 switches we run PVST on each of the 4 VLAN's in use. I find however
that two of the links between edge and core are not working at layer 3 level. CDP is ok and when I do a 'sho int' at either end of the link line, protocol etc is up, Speed and Duplex settings show 1000/full. I think it relates to the PVST as I found that the two trunk ports on the Core (which is the root primary on each vlan)
that don't have layer 3 connectity both appear in blocking state when I do 'sho spanning-tree summary'? It does not affect all the vlans as the other two sho learning etc etc then fwding after I do a 'shutdown' on the trunk ports. The two ports in blocking mode remain in blocking no change - I also noticed that when I do 'sho spanning tree detail' the tx and rx BPDU count is identical on those two ports. All the trunk ports are configured identically. Does anyone have any ideas on troubleshooting this.....
I have tried the usual playing with 'portfast trunk', shutting down ports etc to try to get them working but to no success. Any help would be appreciated...........

 

[unclerico]

I think it relates to the PVST as I found that the two trunk ports...both appear in blocking state

So your Core switch is the primary root of all of your spanning-tree's, but it says that two of its ports are in blocking state?? That can't be right. By default all ports on the root bridge are designated ports and don't block, it's the downlevel switches that negotiate designated/root/blocking ports. You say that each access layer switch is connected to the core with a single connection, but this can't be true if you are having spanning tree issues, you must have redundant connections somewhere??

don't have layer 3 connectity both appear in blocking state

Spanning-tree operates at Layer 2 so layer 3 issues should have no bearing on its operation

Perhaps posting some configs and/or some sh spanning-tree output would help

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