I'll take a shot at helping...
In our OOB Virtual Gateway deployment of NAC 4.6 we are running 7960's on 4506's with PoE blades. Computers are connected through the phones.
In our deployment CDP has nothing to do with NAC...as I understand it.
We are using SNMP Mac-Notifications so NAC is waiting to learn about MACs on each port. Our phone MACs are filtered in NAC to: "Ignore"
When the Switch sends the Mac-Notification to NAC, the IP Phone MAC addresses are Ignored, no action is taken.
here's a port config:
interface FastEthernet3/18
switchport access vlan 20
switchport mode access
switchport voice vlan 40
spanning-tree portfast
we had a very strange issue where about 25% of NAC-ed users were getting booted back to the Auth Vlan once a day, twice a day, twice a week? It was very random. A couple of users were getting thrown into the Auth Vlan every minute. I had to un-NAC their switch port to get them (and me) some relief.
In the end we found that the 7960's of the Users experiencing the issue were not in the Filter List on NAC. NAC was getting notified about the Phone MAC and toggling the port to the Auth vlan. This of course had no impact on the phone (on the Voice Vlan.) But the PC was getting dumped into the Auth Vlan so the Agent had to rerun/reauth.
Big caveat: I'm a NAC Novice. I'm not making any claims that CDP is irrelevant, unnecessary, or otherwise dismissable. I'm just sharing my microscopic experience with our NAC install.
HTH
ps. we now use Profiler to populate the Filter list. it wasn't yet in production when we had the issue.
