Dell switch port showing MAC address of device after it has been removed

We have recently purchased some Dell N3048 and N3024 switches.  The ports are configured as general ports.  We are using clearpass to authenticate all the connections.  We also use Polycomm C600 phones with Lync and those are connected to the switches.  We then plug in our PCs to the PC port on the Lync phones and they connect to the network through the phone.   When we run the command show dot1x interface gi1/0/1, we see both MAC addresses as authenticated.  This works great.  Now we have found that when we swap out the PC, the MAC address of the old PC still shows up as authenticated when we run the show dot1x command.  Once the port is reset or if we unplug the phone, the old MAC address gets cleared out.  We are new to these Dell switches and are not sure exactly what to look for.  Is this an authentication thing or a MAC address ageing thing or something entirely different?  Here is the port configuration:

switchport voice detect auto
spanning-tree portfast
switchport mode general
switchport general allowed vlan remove 1
dot1x port-control mac-based
dot1x max-users 2
dot1x mac-auth-bypass

Of course the dot1x max-users 2 command is how we found this issue because when the old MAC remains, we can't add a new PC to that port because it becomes a 3rd device and will not get authenticated.  I have also set the switch port as an access port and it behaves the same way.  Both devices connect and work fine, but when i disconnect the PC from the phone and run a show mac address-table interface gi1/0/1, both MACs still show up.  The access port config looks like this:

switchport voice detect auto
spanning-tree portfast
switchport access vlan xxx
dot1x port-control force-authorized
dot1x max-users 2

Any assistance would be greatly appreciated.


Thanks,
Johnny Holston
jdholstonAsked:
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Craig BeckCommented:
It's doing exactly what you're configuring it to do.

Setting the max-users tells the switch to only allow the number of MAC addresses learned up to that limit.  You're effectively saying allow the first 2 then no more.  Shutting the port down makes the switch forget the MAC addresses.
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kevinhsiehCommented:
As I recall, it is up the the phone to tell the switch when a device gets disconnected from the phone. Otherwise,  how is the switch supposed to know? I had to do this with Avaya phones and Cisco switches. Look at the documentation for your phones.
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Craig BeckCommented:
The phone doesn't tell the switch that the device has disconnected - that never happens.  The MAC address just stales out after a timer expires.
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