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Computer Names Do Not Resolve When Used in a UNC Path

Updated: March 28, 2005

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

This problem typically occurs when you use Run to access a shared folder and you specify a path in the form \\server name\shared folder name. If the UNC path does not resolve, you will see a “…network resource not found” error. This can also happen when you use the net use command to map a network drive.

Cause

Usually, UNC path names cannot resolve because Windows Firewall is preventing access to a naming service, such as WINS or DNS. To solve this problem, you need to add a port or a service to the Windows Firewall exceptions list on the server that is running the naming service.

This can also be caused if you're using NetBIOS and you have enabled the Prohibit unicast response to multicast or broadcast requests policy setting. If this policy setting is enabled, and a computer broadcasts a NetBIOS name query request to resolve a name, the unicast response from the target computer will be dropped by Windows Firewall. To fix this, you need to disable the Windows Firewall: Prohibit unicast response to multicast or broadcast requestspolicy setting.

Solution

If your organization uses WINS for name resolution, add UDP port 137 to the Windows Firewall exceptions list on your WINS server.

To add UDP port 137 to the Windows Firewall exceptions list
  1. Open Windows Firewall, and then click the Exceptions tab.

  2. On the Exceptions tab, click Add Port.

  3. In the Add a Port dialog box, in Name, type a friendly name for the port exception (for example, UDP port 137).

  4. In Port number, type 137, and then click the UDP option button.

If your organization uses DNS for name resolution, add UDP and TCP port 53 to the Windows Firewall exceptions list on your DNS server.

To add UDP port 53 and TCP port 53 to the Windows Firewall exceptions list
  1. Open Windows Firewall, and then click the Exceptions tab.

  2. On the Exceptions tab, click Add Port.

  3. In the Add a Port dialog box, in Name, type a friendly name for the port exception (for example, TCP port 53).

  4. In Port number, type 53.

  5. Click the TCP option button, and then click OK.

  6. On the Exceptions tab, click Add Port.

  7. In the Add a Port dialog box, in Name, type a friendly name for the port exception (for example, UDP port 53).

  8. In Port number, type 53.

  9. Click the UDP option button, and then click OK.

If you use NetBIOS and UNC path names cannot resolve after you open the appropriate ports on your WINS server or DNS server, then try disabling the Windows Firewall: Prohibit unicast response to multicast or broadcast requestspolicy setting.

Disable the Prohibit unicast response to multicast or broadcast requests policy setting
  1. Open the Group Policy Object Editor snap-in to edit the Group Policy object (GPO) that is used to manage Windows Firewall settings in your organization.

  2. Open Computer Configuration, open Administrative Templates, open Network, open Network Connections, open Windows Firewall, and then click either Domain Profile or Standard Profile.

  3. Double-click Windows Firewall: Prohibit unicast response to multicast or broadcast requests, and on the Settings tab, click Disabled or Not Configured.

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