Port 137 firewall traffic

Posted on 2008-11-13
Last Modified: 2013-11-25
Where does it come from?
Question by:MarcVar
    LVL 10

    Assisted Solution

    Basically netBIOS name service traffic

    Author Comment

    Why is that traffic trying to contact servers outside the firewall?
    LVL 10

    Assisted Solution

    netbios is not routable - it just goes everywhere... hence why you block it on firewalls

    Author Comment

    I can deny the outbound traffic for port 137, but I am trying to determine why this traffic is being generated to specific servers on the internet from my workstation.
    LVL 38

    Accepted Solution

    Port 137 TCP is a netbios/WINS port. It is used for WINS connections to remote sites or subnets.

    If you have no remote sites, it is recommended you block traffic to that port to outside the LAN firewall. But it is needed to computers within the firewall. More to follow:
    LVL 38

    Expert Comment

    I promised "More To Follow" and lost track of this post: sorry about that


    There are two ways file and printer sharing over a VPN connection are perfomed on a network. Both ways are performed by the server at the same time. One is the old school way, and the other is the newer way:

    Port 137 comes in during the old school way:

    --Old school way is to create a WINS connection between the site domain master browsers. (Those are usually the PDCe's)

    --New school way is to get SMB shares going through the tunnel on port 445 and Netbios datagram port 139. Now some ISP's block port 445 due to the vulnerabilities of that data. Also, some routers are now encrypting port 445 to secure the shared traffic. So, this setup depends upon what is offered to you.

    Sorry again for not replying earlier. I hope i just redeamed myself.


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