Server Message Block SMB Protocol

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Server Message Block (SMB) Protocol

• CPE302 TCP/IP Network Lab 2004
• Dome Potikanond
• Sakgasit Ramingwong

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SMB Protocol

• Server Message Block (SMB) protocol is a protocol
  for sharing files, printers, serial ports, and
  communications abstractions such as named pipes
  and mail slots between computers
• Developed in 1985 by IBM
• Also known as Session Message Block and Common
  Internet File System (CIFS)

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SMB Protocol

• Client server, request-response protocol
• Servers make file systems and other resources
  available to clients on the network
• Client computers may have their own hard disks,
  but they also want access to the shared file
  systems and printers on the servers

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SMB Protocol

• SMB Can run over multiple protocols

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SMB Header
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SMB Header

• COM
• Protocol commands.
• RCLS
• Error Code Class.
• REB/FLG
• REB reserved field is associated with the Core
  protocol only.
• The Flag field appears in protocol versions later
  than the Core protocol.
• Tree ID
• Uniquely identifies a file sharing connection
  between consumer and server where this protocol
  uses a server-based file protection.
• Process ID
• Identifies a specific consumer process within a
  virtual connection.

• User ID
• Used by the server to verify the file access
  permissions of users where consumer-based file
  protection is in effect.
• Multiplex ID
• Used by the server to verify the file access
  permissions of groups where consumer-based file
  protection is in effect.
• WCT
• Number of parameter words.
• VWV
• Variable number of words of parameters.
• BCC
• Number of bytes of data which follow.
• BUF
• Variable number of data bytes.

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Simple SMB Connection

• 1. Establish a virtual connection.
• 2. Negotiate the protocol variant to speak.
• 3. Set session parameters.
• 4. Make a tree connection to a resource.

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SMB Protocol Variants

• Core of SMB protocol variants
• connecting to and disconnecting from file and
  print shares
• opening and closing files
• opening and closing print files
• reading and writing files
• creating and deleting files and directories
• searching directories
• getting and setting file attributes
• locking and unlocking byte ranges in files

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Security

• The SMB model defines two levels of security
• Share level
• Protection is applied at the share level on a
  server.
• Each share can have a password, and a client only
  needs that password to access all files under
  that share.
• User Level
• Protection is applied to individual files in each
  share and is based on user access rights.
• Each user (client) must log in to the server and
  be authenticated by the server.
• When it is authenticated, the client is given a
  UID which it must present on all subsequent
  accesses to the server.

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SMB Clients and Servers Currently Available

• Clients
• smbclient from Samba
• smbfs for Linux
• SMBlib (an SMB client library that is in
  development)
• Server
• Samba
• Microsoft Windows 95 and above
• The PATHWORKS family of servers from Digital
• LAN Manager for OS/2, SCO, etc
• VisionFS from SCO
• TotalNET Advanced Server from Syntax
• Advanced Server for UNIX from ATT (NCR?)
• LAN Server for OS/2 from IBM

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Samba

• Samba is an Open Source/Free Software suite that
  provides seamless file and print services to
  SMB/CIFS clients
• Samba is can be run on a platform other than
  Microsoft Windows, for example, UNIX, Linux, IBM
  System 390, OpenVMS, and other operating systems
• Samba uses the TCP/IP protocol that is installed
  on the host server
• When correctly configured, it allows that host to
  interact with a Microsoft Windows client or
  server as if it is a Windows file and print
  server
• www.samba.org

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What Samba does

• File print services
• Authentication and Authorization
• Name resolution
• Service announcement (browsing)
• Windows Domain Controller

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SambaComponents

• Samba has
• 2 client applications
• smbfs
• smbclient
• 1 server application
• smbd
• Depends on the type of sharing used

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Samba Components

• smbd
• Runs in the background
• Provides access to shared directories and
  printers
• Access controlled by username and password
• smbfs
• Runs in the background
• Allows a remote directory to be mounted as a
  device
• smbclient
• Similar to FTP application
• Moves files from and to SMB server

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Samba Utilities

• smbclient
• A simple SMB client, with an interface similar to
  that of the FTP utility.
• nmblookup
• A NetBIOS name service client.
• Nmblookup can be used to find NetBIOS names on a
  network, lookup their IP addresses, and query a
  remote machine for the list of names the machine
  believes it ownes.
• swat
• The Samba Web Administration Tool.
• Swat allows you to configure Samba remotely,
  using a web browser

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Share

• The computer name and share name are required to
  access a shared resource.
• Share names are essentially the same as directory
  names.
• Computer names under Samba can be either a
  NetBIOS computer name, an IP address, or a domain
  name that resolves to an IP address.

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Universal Naming Convention (UNC)

• UNC is a naming convention used by Microsoft.
• It allows a file name to specify the computer
  that the file is located in addition to any
  subdirectories.
• A typical Windows path name looks like
  \dir1\dir2\filename.txt
• A UNC with a computer name and share name looks
  like \\computer1\share1\dir1\dir2\filename.txt

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Configuring samba

• Modify /etc/smb.conf
• Linuxconf
• swat (Samba Web Administration Tools)

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Linuxconf
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SWAT
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Security

• samba provides 3 security levels
• No security
• Use account name
• Use name and password