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How to force SMB over TCP when NetBIOS is disabled on an Active Directory domain controller

Last Updated:


Applies to

Data ONTAP 7-mode


Domain controllers in a Windows Active Directory domain may have NetBIOS disabled. The filer will still attempt to use NetBIOS to communicate with the domain controllers and may time out when port 139 is blocked.

How can you force the filer to use Kerberos and port 445 to communicate with the domain controllers instead of NetBIOS and port 139?

Background Information: SMB over TCP vs. SMB over NBT

The SMB (Server Message Block) protocol is used among other things for file sharing in Windows NT / 2000. In Windows NT it ran on top of NBT (NetBIOS over TCP/IP), which used ports 137, 138 (UDP) and 139 (TCP). In Windows 2000, Microsoft added the possibility to run SMB directly over TCP/IP, without the extra layer of NBT. For this they use TCP port 445.

If the domain controller has NBT enabled, it listens on UDP ports 137, 138, and on TCP ports 139, 445. If it has NBT disabled, it listens on TCP port 445 only.


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