Network File System Protocol

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Network File System Protocol

• By Authentication Experts

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Introduction

• Provides transparent remote access to shared file
  across the network
• Portable across different architecture and
  operating system

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Introduction

• Aim to provide the following logical view

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Introduction

• First version developed by Sun Microsystems for
  internal research
• Version 2 introduced in March, 1989 defined in
  RFC 1094
• Version 3 introduced in June, 1995 defined in RFC
  1813
• Version 4 introduced in December, 2000 defined in
  RFC 3031 revised in RFC 3530, April 2003

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Introduction to File System

• A file system is a way of storing data on a
  medium the way it is organized and managed
• Every file is represented by an inode
• A file descriptor holding, among other things,
  file access permissions, physical block addresses
  holding data, etc.
• The NFS servers task is to give clients the
  inodes they want to access
• An NFS server gives an additional net layer
  allowing remote machines to handle the inodes

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The NFS Protocol

• NFS is built from 4 distinct protocols
• nfs
• - File creation, searching, reading, writing
• Authentication and statistics
• mountd
• - Mounting of exported systems for access via
  nfs
• nsm
• - Network Status Monitor
• - Monitors a client or server machines status
• nlm
• - Network Lock Manager
• - Avoid simultaneous data modification by
  multiple clients

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The NFS Protocol
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How does RPC work?
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Port Mapper Analogy
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Port Mapper Analogy
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File Handling in NFS

• The protocol revolves around the filehandle
• -A data structure allow unique identification of
  a file system object
• -Contains the file inode and an entry
  representing the device where the file resides
• How does a server know which file/directory the
  client needs to access?
• - At first, client obtains a file handle for
  root of the file system
• - File handle is opaque to the client
• - Client sends file handle to server when
  referencing a file/directory
• - No need to use the full path names
• The file handle contains whatever information the
  server needs to distinguish an individual file

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The NFS Protocol
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The NFS Protocol

• Each relies on Remote Procedure Calls(RPC)
  andPortmap(also calledrpc.portmap).
• An RPC server tells portmap which port will be
  used and the managed RPC number
• A client contacts portmap to get port number of
  desired server program
• RPC packets are addressed to the corresponding
  port

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Sequence Diagram
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Statelessness

• What is statelessness ?
• - Server does not need to maintain protocol
  state about its client
• - Server does not keep previous request
  information
• - Client keeps track of all information required
  to send requests to the server
• Advantage
• - If server crashes, no state information lost
• - Client needs only retransmit a request until
  the server responds

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NFS Procedure
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NFS Version 3

• Introduced in June,1995, described in RFC 1813
• Support for 64-bit file sizes and offsets, to
  handle files larger than 4 GB
• Support for asynchronous writes on the server, to
  improve write performance
• Using TCP as a transport made using NFS over a
  WAN more feasible

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NFS Version 4

• Introduced in December,2000(RFC 3010) and revised
  in April,2003, described in RFC 3530
• Introduces a stateful protocol
• Mandates strong security
• Performance improvements

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• Thank
  you