Difference Between NetBIOS & SMB

What is NetBIOS

NetBIOS is an acronym that stands for Network Basic Input Output System. It might seem like a protocol but isn’t one, it is an API that provides session layer services that allow applications on different computers to communicate over the LAN. In modern networks NetBIOS runs over TCP/IP via the NetBIOS over TCP/IP or commonly known as NBT protocol. This results in each computer on the network having a NetBIOS name along with the IP Address corresponding to the host name.

  • NetBIOS-NS: Name service, used for name registration and resolution like DNS. In order to initiate a session, an application has to register its NetBIOS name using this service. In NBT this service runs on UDP port 137 and can also be seen rarely on TCP port 137.
  • NetBIOS-DGM: Datagram distribution service, connection-less. Runs on UDP (as you might’ve guessed) port 138. As it is connection-less service, the application is responsible for error detection and data recovery.
  • NetBIOS-SSN: Session service for connection-oriented communications. This service lets two devices establish a connection and also has error detection and recovery unlike datagram distribution service. It runs on TCP port 139.

What is SMB

SMB stands for Server Message Block. It is an application layer protocol that is mainly used for providing shared access to things like files and printers on the network. For instance, whenever you send a print request to the printer that is present inside you LAN, SMB is used to send the print request. It is based on request-response model.

  • Run directly over TCP port 445. On Windows SMB can run directly over TCP/IP without the need for NBT, using services like microsoft-ds that allow direct hosting of SMB via port 445.
  • Run via NetBIOS API which in turn can run in several different ways — on UDP ports 137, 138 or TCP ports 139 as we saw earlier in the NetBIOS section.




Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store
Yashwardhan Chavan

Yashwardhan Chavan

“He who has a Why to live for can bear almost any How” | ethical hacker and cyber security enthusiast and I like to read and write.