In a previous post titled ADAC and VLAN Configurations I described some issues we were having with some of our switches where VLAN memberships were mysteriously changing. We suspected ADAC and we were right on with our suspicions.
We performed some exhaustive testing with ADAC over the past few weeks and can confirm, as Roberto alluded too, that ADAC will dynamically reconfigure any switch port that has ADAC enabled to the VLAN membership and PVID setting that was set when ADAC was first enabled on the switch port. In our tests we configured an edge port as a member of VLAN 10 and then enabled ADAC on that port. We then added the edge port to VLAN 11, removing it from VLAN 10. When the port went into an oper-down state ADAC added the edge port back to VLAN 10 and removed it from VLAN 11. We confirmed the same behavior with respect to the PVID changing.
In short if you need to make a VLAN membership or PVID change to an ADAC enabled port you MUST disable ADAC on the port before making the change and then re-enable ADAC when you have completed your change. As a side note any Nortel IP phone that is connected to the port will most likely timeout and reboot itself when you disable ADAC.
While I don’t necessarily disagree with the behavior it would be nice for either the CLI of Device Manager to alert someone if they tried to change the VLAN membership of a port that had ADAC enabled. (hint hint Nortel)