I am working out a lab where I have 2 4506e core switches and 3 3750 access switches. Each access switch is connected by a fiber connection to one of the core switches. For example G1/0/49 goes to Core A on Gig2/1 and G1/0/50 goes to Core B on Gig2/1. L2 configuration with a L2 EtherChannel between the core switches as members of Po1. When all switches are operational, I can check each switch to see the trunk status, all VLANs (each switch has its own VLAN, VLAN1 through VLAN5) are part of the management domain and are allowed on the trunk. However, on two switches, when it comes to VLANS in a spanning tree forwarding state some of the VLANs are missing (pruning is turned off) or simply report "none". My confusion comes from, obviously not knowing STP very well and reading Cisco information that seems to point that when a backup port is in a blocking state (and I would assume in a L2 environment) that all is normal. As you want the port not to pass transit traffic and to move into a forwarding state if the root port on that switch (the other fiber connection) should go down. I can verify this by unplugging the fiber from the root port to see the VAN go down and come back up, with the formally backup port now fully operational. BTW all VLANS and trunks are operational. Am I understanding this correctly? Or should I see all VLANs in the spanning tree forwarding state (I do have one switch that reports this way) and what I am seeing is the result of a built in loop somehow? Anyone who has experience with this, I'd like to hear from you. Configs are attached with: sh int trunk sh config sh vtp status sh spanning-tree detail sh etherchannel sh int po1 realized access switches were not set to client, no change in problem.
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