Cisco NAC Troubleshooting Tip: Windows Firewall Using Wrong Profile

NetCraftsmen®

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.

HKLMSOFTWAREMicrosoftWindowsCurrentVersionGroup 
PolicyHistoryNetworkName

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

http://www.gpoguy.com/FAQs/tabid/57/agentType/ViewType/PropertyTypeID/4/Default.aspx

http://technet.microsoft.com/en-us/library/bb878049.aspx

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Nick Kelly

Cybersecurity Engineer, Cisco

Nick has over 20 years of experience in Security Operations and Security Sales. He is an avid student of cybersecurity and regularly engages with the Infosec community at events like BSides, RVASec, Derbycon and more. The son of an FBI forensics director, Nick holds a B.S. in Criminal Justice and is one of Cisco’s Fire Jumper Elite members. When he’s not working, he writes cyberpunk and punches aliens on his Playstation.

 

Virgilio “BONG” dela Cruz Jr.

CCDP, CCNA V, CCNP, Cisco IPS Express Security for AM/EE
Field Solutions Architect, Tech Data

Virgilio “Bong” has sixteen years of professional experience in IT industry from academe, technical and customer support, pre-sales, post sales, project management, training and enablement. He has worked in Cisco Technical Assistance Center (TAC) as a member of the WAN and LAN Switching team. Bong now works for Tech Data as the Field Solutions Architect with a focus on Cisco Security and holds a few Cisco certifications including Fire Jumper Elite.

 

John Cavanaugh

CCIE #1066, CCDE #20070002, CCAr
Chief Technology Officer, Practice Lead Security Services, NetCraftsmen

John is our CTO and the practice lead for a talented team of consultants focused on designing and delivering scalable and secure infrastructure solutions to customers across multiple industry verticals and technologies. Previously he has held several positions including Executive Director/Chief Architect for Global Network Services at JPMorgan Chase. In that capacity, he led a team managing network architecture and services.  Prior to his role at JPMorgan Chase, John was a Distinguished Engineer at Cisco working across a number of verticals including Higher Education, Finance, Retail, Government, and Health Care.

He is an expert in working with groups to identify business needs, and align technology strategies to enable business strategies, building in agility and scalability to allow for future changes. John is experienced in the architecture and design of highly available, secure, network infrastructure and data centers, and has worked on projects worldwide. He has worked in both the business and regulatory environments for the design and deployment of complex IT infrastructures.