User cannot log in to the domain controller through the router or browse network resources through the network neighborhood

[TCC_2]

Core Issue

The issue is most likely caused by User Datagram Protocol (UDP) ports not being permitted or forwarded through the router.

Resolution

To resolve this problem, issue the ip helper-address command or reconfigure the Access Control Lists (ACLs) to permit UDP ports 137, 138 and 139. 

For more information on configuring the ip helper-address command, refer to the ip helper-address section of Cisco IOS Command Reference.