Should I allow Netbios UDP port 137 out on our primary DNS server??

Posted on 2008-06-13
Medium Priority
Last Modified: 2013-11-25
Should I allow Netbios UDP port 137 out on our primary DNS server??  Could I get an explanation on why this would or wouldnt be needed.  I am just seeing a lot of outgoing traffic on port 137.

Question by:mkurtzhals
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Expert Comment

ID: 21780202
If your network is working well without it, keep it blocked.

Author Comment

ID: 21781710
Could I please get an explanation why my DNS server would be attempting to send all this UDP traffic out?

Expert Comment

ID: 21781763
If you want to minimize upd traffic :

1. Disable service "NetBios TCP/IP helper"
2. Check Advanced properties of TCP/IP connection and Disable Netbios.

LVL 71

Accepted Solution

Chris Dent earned 2000 total points
ID: 21835282


You'll need the TCP/IP NetBIOS Helper if you want to use File and Printer Sharing on the server. But I'd agree with disabling NetBIOS in the TCP/IP properties, I never liked it.

The traffic in question is NetBIOS-NS, NetBIOS Name Service. It's responsible for all sorts, including registering names on the NetBIOS network.

It's nothing to do with DNS so don't feel that blocking it will impact the functionality of your DNS Server.

It's also unlikely to be malicious traffic if it's Outbound, if you've curious about what's in those requests I'd recommend putting a Packet Sniffer onto the machine. I like WireShark for such tasks, you can grab that here:




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