FTP, TFTP, and NFS

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FTP, TFTP, and NFS

• LESSON 25
• (December 1, 1995)
• Daniel Z. Tabor Jr.
• New Jersey Institute of Technology

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OutlineFTP, TFTP, and NFS

• File Sharing
• On-line Access
• Whole-file Copying
• Requirements
• Version Control
• File Transfer Protocol (FTP)
• Control and Data Transfer Connections
• Interactive Transfer System
• Anonymous FTP

• Control and Error Information Messages
• Trivial File Transfer Protocol (TFTP)
• Network File System
• NFS Architecture
• Remote Procedure Call
• Message Specification
• External Data Representation (XDR)

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File Sharing

• Client / Server File Interaction
• File sharing is used to reduce storage costs.
• Remote file access extends the reach of system
  resources, further leveraging these costs.
• Distributed file storage and remote access allows
  multiple users to work on and modify the same
  file from anywhere on the network.
• There are two distinct forms of file sharing.

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File SharingOn-line Access

• On-line access
• Allows multiple programs to access a single file
  concurrently.
• This should be integrated with local files and
  access should be transparent.
• Advantage - no visible changes in the
  environment.
• Disadvantage - congested networks make file
  access slower.

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File SharingWhole-file Copying

• Whole-file copying
• This transfer scheme requires a two-step process
  in which the user first obtains a local copy of a
  file and then operates on it.
• This is not integrated with the local file-system
  and requires the use of a client program.
• Advantage - efficient manipulation operations.
• Disadvantage - applying updates to stored file on
  server.

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File SharingRequirements

• Both methods of file sharing are difficult with
  heterogeneous machines.
• They must agree on
• Authorization.
• Notions of file ownership and access protections.
• Data formats.

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File SharingVersion Control

• Another major concern when sharing files is
  version control
• Each user may make changes either locally or
  shared remotely.
• The operating system must know which users
  changes to write first, and then notify all other
  users that the file has now changed.
• This same issue plagues many different computer
  science areas.

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File Transfer Protocol (FTP)

• File Transfer Protocol (FTP) - is a reliable file
  transfer protocol used within TCP/IP.
• It offers
• Interactive access with a human friendly
  interface.
• File format specifications (ASCII, Binary)
• Authentication Control (including login names and
  passwords)

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Control andData Transfer Connections

• FTP allows concurrent access by multiple clients,
  using the transmission control protocol.
• Slave processes are used in FTP to accept and
  handle the control connection from the client.
• However, they use an additional process (or
  processes) to handle the separate data transfer
  connection(s) needed to send and receive files.

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Image source Internetworking with TCP/IP vol I
(1995 Prentice Hall, Douglas Comer)
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Control andData Transfer Connections

• Control processes and the control connection
  remain alive as long as the FTP session is
  going.
• A separate data transfer connection is setup and
  taken down for each file transfer.

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Control andData Transfer Connections

• In addition to passing user commands to the
  server, FTP uses the control connection to allow
  the client and server control processes to
  coordinate their use of
• Dynamically assigned TCP protocol ports.
• The creation of data transfer processes that use
  those ports.

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Control andData Transfer Connections

• FTP uses Telnet's Network Virtual Terminal
  specification when passing data across the
  control connection.
• The basic definition of service is only used, no
  option negotiation is allowed.
• Commonly, FTP is shown to conceptually reside
  above TELNET in a layered protocols stack,
  strictly for this reason.

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Interactive Transfer System

• Interactive Transfer System (client performs
  operations repeatedly)
• Read a line of input.
• Parse the line to extract the command and
  arguments.
• Execute the command with its arguments.

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Anonymous FTP

• Anonymous FTP access means the user does not need
  an account or password, but can freely login to a
  remote machine.
• Login name Anonymous
• Password Guest or full e-mail address.

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Anonymous FTPTerminal-Based

• When anonymously logging into a remote site via
  an text-based connection, the user must
  explicitly interact with the machine using a set
  of commands (? from prompt).
• To download a file, the user must
• Login and send guest password
• Select the directory the file exists in.
• Change the transfer option based on file type.
• Explicitly get the file and then exit.

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Anonymous FTPWWW-based

• When accessing a FTP server through a web client
  (Netscape), no interactive commands are needed.
• Differences between terminal and WWW access
• No login required or file-type transfer option
  setting.
• Graphical traversal of subdirectories.
• No file uploading (PUT) allowed, only GET.
• Applications can be spawned locally based on file
  type transferred.

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Control and ErrorInformation Messages

• Control and error information messages between
  the FTP client and server begin with a 3-digit
  number followed by text.
• The software interprets the number.
• The text is solely meant for humans.

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Control and ErrorInformation Messages

• The PORT command, used by a client, reports that
  a new TCP port number has been obtained for use
  in a data connection.
• The port number used for this connection
  increases each time a connection is made (by any
  client).
• To see more detailed interaction information,
  execute ftp with verbose mode on
• ftp -d hertz.njit.edu

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Trivial File TransferProtocol (TFTP)

• Trivial File Transfer Protocol (TFTP) - This
  simple transfer protocol
• Does not need a reliable stream transport service
  (uses UDP).
• Is intended for applications that do not need
  complex interactions between the client and
  server.

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Trivial File TransferProtocol (TFTP)

• TFTP
• Restricts operations to small file transfers.
• Does not provide authentication.
• And is much smaller (software) than FTP.

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TFTPEncoding and Transmission

• TFTP is commonly encoded in ROM (Read-Only
  Memory) on workstations and is used to obtain the
  initial bootstrap memory image (BOOTP).
• A TFTP transmission is symmetric (implements a
  time-out and retransmission mechanism) which
  helps ensure transfer will not fail after a
  single packet loss.

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TFTPEncoding and Transmission

• Sorcerers Apprentice Bug
• This anomaly arises when an ACK for data packet K
  is delayed, but not lost.
• It creates a cycle which continues indefinitely,
  with each packet transmitted at least twice.
• TFTP supports multiple file types and can be
  integrated with electronic mail.

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Network File System (NFS)

• Network File System (Sun NFS)
• Provides on-line shared file access that is
  transparent and integrated within operating
  systems.
• NFS is usually embedded within the UNIX operating
  system and is commonly referred to NFS Mount.
• NFS refers to the complete family of products
  (Sun calls it Open Network Computing).

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Network File System (NFS)

• NFS has been extended from UNIX to allow PCs to
  access other computers using PC-NFS.
• NFS provides a resource-sharing network system
  with similar features to Novell Netware or
  Microsoft LAN Manager.

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Network File System (NFS)

• The major difference is that NFS bases the major
  part of its functionality on the native O.S.
  available on the server hosts.
• NFS is not proprietary, yet is just as if not
  more powerful than commercial resource-sharing
  systems.
• NFS is usually implemented over TCP/IP, but is
  not exclusive to it.

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NFS Architecture

• NFS is made up of three layers
• RPC - which defines the format of messages used
  by remote procedure calls.
• XDR - the eXternal Data Representation is a
  consistent representation of data between
  different machine architectures.
• NFS - the Network File System is an application
  interface for file transfer, access, and
  management.

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Network File System (NFS)
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NFS Architecture

• The functionality of the layers maps very closely
  to the OSI functionality available in its
  equivalent layers (application, presentation,
  session).
• The operation of NFS is based on a stateless
  relationship between the client and server.
• NFS uses UDP and fixed retransmission time-outs
  to provide a low consistent delay over local area
  networks.

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Remote Procedure Call (RPC)

• Remote Procedure Calls (RPC)
• These are general purpose remote execution
  mechanisms which hide all details of lower-level
  protocol use.
• They are used (in part) to implement NFS and
  other client / server programs.
• RPC is used in realizing distributed computing
  systems.

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Remote Procedure Call (RPC)

• RPC and distributed computing has the ability to
  reduce the amount of data transferred across a
  network, especially where databases are
  concerned.
• The RPC protocol sends messages over the network
  to handle transactions, verification, and
  authorization.

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RPC Message Specification

• Transaction ID
• Call / Response
• RPC Protocol Version Number
• Program Number
• Portmapper
• NFS
• Mountd
• Rstatd

• Program Version Procedure Number
• Authorization Information
• User ID
• Group ID
• UNIX Machine Name
• Authorization Verification
• Procedure Call Parameters

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External Data Representation (XDR)

• External Data Representation (XDR)
• Provides a way to pass data among heterogeneous
  machines without the need for conversion
  routines.
• A program using XDR must know (in advance) what
  type of data to expect and provision for it
  accordingly.
• In an OSI system, each value is labeled with its
  type and size.

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External Data Representation (XDR)

• XDR defines data in multiples of four bytes
  (32-bits), which is a definition of how the data
  should formed before network transmission.
• An NFS client formats data based on XDR so an NFS
  server will translate data into the form
  understood by the destination computer.
• UNIX and PC operating systems use the combination
  of NFS, RPC, and XDR to provide distributed
  system features.

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QuestionsFTP, TFTP, and NFS

• Name equivalent OSI layer protocols to those
  found in NFS (NFS, RPC, XDR).
• How do FTP and Trivial FTP differ? In what ways?
• What part of the Telnet protocol does FTP borrow
  or use?
• Why are two end-to-end connections required to
  transfer a single file? Could it be done with
  one?
• How do WWW browsers shield an end-user from
  having to specify a file type to download?

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Reference MaterialsFTP, TFTP, and NFS

• RFC 959 File Transfer Protocol - FTP
  (http//www.cis.ohio-state.edu/htbin/rfc/rfc959.ht
  ml)
• PC-NFS Product Home Page (http//www.intergraph.c
  om/nfs/nfs_ovr.htm)
• Protocols used in the World-Wide Web
  (http//www.w3.org/hypertext/WWW/Protocols/Relevan
  tProtocols.html)
• Internet Information Quick Reference
  (http//www.kme-lab.co.jp/internet/resource.html)
• RFC 1350 TFTP PROTOCOL (REVISION 2)
  (http//www.cis.ohio-state.edu/htbin/rfc/rfc1350.h
  tml)