I am involved in a campus roll out using 3750X and Nexus 7009 core.
Recently while troubleshooting a fibre uplink I have run accross an issue with default behaviors of these two switchs with regard to tagging the native vlan.
After much searching I cannot find any documentation regarding the support for this command being removed from the 3750X.
My version is 12.2(58)SE2.
Turns out that you can no longer enter this command and it is enabled by default on the trunk, which is evident by the show interface switchport command.
The problem is that to be compatible I must enable this on the Nexus. The command is still available in NX-OS 6.1(1).
Without doing this a trunk that only permits vlan 1 on both ends will be in spanning tree status BKN*2 Network P2P BA_Inc. on the Nexus end.
An event log STP-2-BRIDGE-ASSURANCE_BLOCK message is logged indicating that the vlan is blocked as a result of not recieving a BPDU on the interface. This is odd behavior as well since a root bridge would not normally be receiving BPDU's from a non-root bridge anyway.
Other info.
Nexus is the root.
Role and Status on 3750x is Altn BLK
The link in question was removed from an etherchannel on both ends and allowed vlans changed to "1" on both ends.
Vlan 1 is not in use, and since the link was flapping I remved it from production to troubleshoot.
Thought I would ask here before reporting this to TAC.
