adam's notes

File and Print Servers

One of the core network functions is to provide shared access to disk and print resources.

  • resource sharing is implemented using a client/server architecture
    • machine hosting the disk or printer is the server
    • server disk configured to allow clients to access it over the network is a fileshare.
    • Machines accessing those resources are the clients
  • fileshare and print server roles may be implemented on a local network using proprietary protocols
    • such as File and Print Services for Windows Networks
  • A file server could also be implemented using TCP/IP protocols, such as File Transfer Protocol (FTP)

Server Message Block

Server Message Block (SMB) is the application protocol underpinning file and printer sharing on Windows networks.

  • usually runs directly over the TCP/445 port
  • has gone through several updates
    • SMB3 as the current version
    • SMB1 has very serious security vulnerabilities and is now disabled by default on current Windows versions

Tip

Support for SMB in UNIX- or Linux-based machines and network attached storage (NAS) appliances is provided by using the Samba software suite.

  • allows a Windows client to access a Linux host as though it were a Windows file or print server

Info

SMB is sometimes referred to as the Common Internet File System (CIFS), though technically that should only be used to refer to a specific dialect of SMB version 1.

Network Basic Input-Output System

The earliest Windows networks used a protocol stack called the Network Basic Input/Output System (NetBIOS) rather than TCP/IP.

  • allowed computers to address one another by name and establish sessions for other protocols, such as SMB
  • As the TCP/IP suite became the standard for local networks
    • NetBIOS was re-engineered to work over the TCP and UDP protocols
    • referred to as NetBIOS over TCP/IP (NetBT)
      • uses UDP/137 for name services and TCP/139 for session services
    • Modern networks use IP, TCP/UDP, and DNS for these functions
      • so NetBT is obsolete
      • NetBT should be disabled on most networks, as it poses a significant risk to security
      • only required if the network must support file sharing for Windows versions earlier than Windows 2000

File Transfer Protocol

The File Transfer Protocol (FTP) allows a client to upload and download files from a network server.

  • often used to upload files to websites
  • uses port TCP/21 to establish a connection and either
    • port TCP/20 to transfer data in “active” mode
    • or a server-assigned port in “passive” mode

Info

  • Plain FTP is unencrypted and so poses a high security risk
  • Passwords for sites are submitted in plaintext
  • There are ways of encrypting FTP sessions, such as FTP-Secure (FTPS) and FTP over Secure Shell (SFTP), and it is the encrypted services that are most widely used now

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