How to enable Windows file sharing on WAN or WLAN thru firewall

Windows File Sharing at LAN environment is common and it is using chatty NetBIOS protocol. NetBIOS is broadcast based(Non-routed) protocol. So, if you are on WAN or WLAN, how you get file sharing function?  Answer is SMB.

The following ports are associated with file sharing and server message block (SMB) communications:

• Microsoft file sharing SMB: User Datagram Protocol (UDP) ports from 135 through 139 and Transmission Control Protocol (TCP) ports from 135 through 139.
  • UDP 137 – NetBIOS Name Resolution
  • UDP 138 – NetBIOS Datagram transmission and reception
  • TCP 139 – NetBIOS Session Service

• Direct-hosted SMB traffic without a network basic input/output system (NetBIOS): port 445 (TCP and UPD).

You need to allow, TCP/UDP port 445 for SMB traffic from firewall

and \\[ip address x.x.x.x] \ [Sharing folder name]

 

Client side

• If NetBT is enabled, client try both port 139 and 445 simultaneously.

– If client got response from port 445(SMB), it sends a RST to port 139, and it’s SMB session to port 445 only.

– If client doesn’t get response from port 445, it will continuously SMB session to port 139 only.

– If no response from both of ports, a session will be failed.

 

– If NetBT is disabled, client will always try to connect to the server with port 445 only.

 

Server side

 

• If NetBT is enabled, the server listens on UDP ports 137, 138, and on TCP ports 139, 445.
• If NetBT is disabled, the server listens on TCP port 445 only.