i have uplinks from core switches that connect to Virgin WAN router configured as access ports and in vlan 999. By mistake a cable is plugged in thats configured in different vlan and has portfast set. This leads to error message of not in common subnet and all ports in vlan999 being blocked until reconvergence.
This seemed to take a long time and I want to avoid it happening again. I think if i set all ports except uplinks with bpduguard so they error disable if a switch is plugged in, this would stop some problems. But would this help protect against the not in common subnet error and blockign affecting all switches on vlan 999?
Is spanning tree detecting a loop when it gives not in common subnet ?Thanks