What is an SMB Port?

Published On - March 27, 2024

The Server Message Block (SMB) protocol is a client-server protocol designed for sharing files, printers, and data over a network. It enables users to interact with remote server files, including opening, reading, moving, creating, and updating. SMB initially operated on NetBIOS over TCP/IP (NBT) and later merged with Microsoft's LAN Manager product. Today, SMB uses port 445.

SMB has undergone significant evolution since its inception. It now supports advanced features such as symbolic links, hard links, and larger file sizes. SMB 2.0 introduced reduced chattiness and improved performance, while SMB 3.0 enhanced security with end-to-end encryption and AES-based signing. These advancements have made SMB a robust and scalable protocol for file and resource sharing in modern network environments.

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How Does the SMB Protocol Work?

In early versions of Windows operating systems, SMB used NetBIOS network architecture for its communication. However, with the advent of Windows 2000, Microsoft transformed SMB to operate on TCP (Transmission Control Protocol) and use a dedicated IP port. This enhancement has been carried forward into subsequent Windows versions. Over the years, Microsoft has steadfastly evolved SMB for both enhanced performance and reinforced security. SMB2 brought about a reduction in chattiness, while SMB3 significantly improved performance in virtualized environments. Additionally, SMB3 introduced support for robust end-to-end encryption, bolstering data protection.

What are Ports 139 and 445?

SMB requires specific ports to facilitate communication between computers and servers: ports 139 and 445. Port 139 is used by older SMB dialects that rely on NetBIOS for communication and establish network connections for shared resources like printers and serial ports, particularly in Windows operating systems. Port 445, on the other hand, is employed by more recent versions of SMB (post-Windows 2000). It leverages the TCP protocol stack and allows SMB communication beyond local networks to the internet. This enables the use of IP addresses for SMB-related activities, such as file sharing and remote access to resources.  

SMB Protocol Dialects

Computer programmers have devised multiple variations of the SMB protocol, each tailored to specific applications. Among these, the Common Internet File System (CIFS) stands out as a notable implementation that facilitates file sharing capabilities. While CIFS may often be misconstrued as a distinct protocol from SMB, they share a common foundation, with CIFS acting as a specialized extension of the broader SMB architecture. Below are some of the most common SMB dialects:

  • CIFS: Common Internet File System (CIFS) is a widely used file sharing protocol designed specifically for Windows servers and their compatible NAS (Network Attached Storage) devices. This protocol enables seamless sharing and exchange of files and directories across connected systems, facilitating efficient data accessibility within Windows-based environments.
  • Samba: Samba is an open-source implementation of Microsoft Active Directory, providing interoperability between non-Windows machines and Windows networks. It allows seamless authentication and authorization processes, enabling non-Windows devices to connect to Windows domains and access shared resources, bridging the gap between disparate operating systems.
  • NQ: NQ stands for NetQOS and is a portable implementation of the SMB protocol developed by Visuality Systems. Its distinguishing feature is its platform independence, allowing it to be deployed on various operating systems, including Windows, Linux, and macOS. This versatility makes NQ a suitable solution for heterogeneous network environments.
  • MoSMB: MoSMB is a proprietary SMB implementation created by Ryussi Technologies. Known for its high performance, stability, and scalability, MoSMB is widely used in enterprise-scale environments. Its closed-source nature provides additional control and optimization capabilities tailored to specific requirements.
  • Tuxera SMB: Tuxera SMB is a proprietary SMB implementation that offers flexibility in terms of deployment options. It can operate either in kernel-mode or user-space mode, catering to different performance and security considerations. This flexibility allows administrators to optimize Tuxera SMB based on their specific network requirements.
  • Likewise: Likewise is a multi-protocol, identity-aware network file sharing protocol acquired by EMC in 2012. It supports both SMB and NFS (Network File System) protocols, providing a comprehensive solution for file sharing between Windows and non-Windows systems. Additionally, Likewise features identity management capabilities, ensuring secure access to shared resources.   

How To Keep SMB Ports Secure

To bolster the security of open network ports, implementing a layered approach is crucial. Enable firewalls or endpoint protection with a blacklist to block malicious IP addresses. Installing a VPN encrypts network traffic, adding an extra layer of protection. Segmenting the network using VLANs isolates internal traffic, reducing the risk of internal attacks. Additionally, implementing MAC address filtering restricts system access to authorized devices, but requires ongoing management. To enhance data-centric security, a comprehensive plan is necessary. Map data and access rights on SMB shares to establish proper permissions. Use data discovery tools to identify sensitive information on SMB shares. Monitor data for suspicious activities that could indicate breaches. By highlighting data at risk and tracking abnormal access patterns, organizations can proactively mitigate cyber threats.

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