This troubleshooting tip pertains to environments that use Cisco NAC in L3 OOB mode and use the Windows Firewall for end computer protection. In this scenario, a problem could occur where the Windows Firewall incorrectly uses the standard profile when it should be using the domain profile. This could cause problems if the Windows Firewall standard profile does not allow remote desktop connections to the end computer. If this was the case, the help desk would not be able to utilize remote desktop to access a computer to provide troubleshooting assistance for end users. With NAC, this could occur with the creation of a new authentication VLAN and associated new DHCP scope. An instance of the problem and solution are shown below.
When a gpupdate occurs, a specific registry value is modified that validates the DNS suffix of the computer when the gpupdate occurred. This registry value is located as shown below.
When the computer IP address changes, the current DNS suffix is compared against the “NetworkName”. If they are the same, the computer continues to use the domain profile. If they are different, the computer uses the standard profile. If the DNS suffix option is not added to the DHCP scope, the “NetworkName” reverts to using the IP subnet as a value to populate the field. This value is updated every time a gpupdate is performed. This is what causes the problem. For example, when a computer is in the access VLAN, the “NetworkName” value could be “10.1.1.0”. When the computer is in the authentication VLAN, the “NetworkName” value could be “10.1.10.0”. Upon IP change, the computer checked the current value and sees that it is different than what was configured in the registry value. This causes the computer to use the standard profile and cause the Windows Firewall to block Remote Desktop traffic.
To reiterate, this problem exists if the DHCP server does not have the correct domain suffix defined. As long as the same domain suffix is used for the access VLAN and authentication VLAN, this problem will not exist.
In researching this problem, I used the links below