We have a system which uses port 139 NetBIOS to broadcast, which in turn allows PC users to map drives to the server. BUT, our firewall team will not allow such traffic across the network. Are they being pedantic and why would they impose such restrictions.

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Dear Jcowie:
NetBIOS over TCP/IP (port 139) is not secured and should be blocked from inbound or outbound access through the firewall to the Internet/DMZ for security reasons. To allow this port through the firewall is to defeat the purpose of having a firewall in the first place. Windows NT uses Port 139 for null sessions and for file sharing; Windows 2000 uses (for SMB) port 445 if port 139 is not enabled.

Hope this provided the information you needed.
Take care,
Luis

This was first published in August 2002

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