Skip to main content
We are redesigning the NetApp Knowledge Base site to make it easier to use and navigate. The new and improved site will be available the first week of October. Check out our video or read this KB article to know more about changes you’ll see on the site.
NetApp Knowledge Base

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.



Registered NetApp customers get unlimited access to our dynamic Knowledge Base.

New authoritative content is published and updated each day by our team of experts.

Current Customer or Partner?

Sign In for unlimited access

New to NetApp?

Learn more about our award-winning Support


******************************************************* *******************************************************