TCP/IP tutorial
RFC 1180

Document Type RFC - Informational (January 1991; Errata)
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Network Working Group                                      T. Socolofsky
Request for Comments:  1180                                      C. Kale
                                                  Spider Systems Limited
                                                            January 1991

                           A TCP/IP Tutorial

Status of this Memo

   This RFC is a tutorial on the TCP/IP protocol suite, focusing
   particularly on the steps in forwarding an IP datagram from source
   host to destination host through a router.  It does not specify an
   Internet standard.  Distribution of this memo is unlimited.

Table of Contents

    1.  Introduction................................................   1
    2.  TCP/IP Overview.............................................   2
    3.  Ethernet....................................................   8
    4.  ARP.........................................................   9
    5.  Internet Protocol...........................................  12
    6.  User Datagram Protocol......................................  22
    7.  Transmission Control Protocol...............................  24
    8.  Network Applications........................................  25
    9.  Other Information...........................................  27
   10.  References..................................................  27
   11.  Relation to other RFCs......................................  27
   12.  Security Considerations.....................................  27
   13.  Authors' Addresses..........................................  28

1.  Introduction

   This tutorial contains only one view of the salient points of TCP/IP,
   and therefore it is the "bare bones" of TCP/IP technology.  It omits
   the history of development and funding, the business case for its
   use, and its future as compared to ISO OSI.  Indeed, a great deal of
   technical information is also omitted.  What remains is a minimum of
   information that must be understood by the professional working in a
   TCP/IP environment.  These professionals include the systems
   administrator, the systems programmer, and the network manager.

   This tutorial uses examples from the UNIX TCP/IP environment, however
   the main points apply across all implementations of TCP/IP.

   Note that the purpose of this memo is explanation, not definition.
   If any question arises about the correct specification of a protocol,
   please refer to the actual standards defining RFC.

Socolofsky & Kale                                               [Page 1]
RFC 1180                   A TCP/IP Tutorial                January 1991

   The next section is an overview of TCP/IP, followed by detailed
   descriptions of individual components.

2.  TCP/IP Overview

   The generic term "TCP/IP" usually means anything and everything
   related to the specific protocols of TCP and IP.  It can include
   other protocols, applications, and even the network medium.  A sample
   of these protocols are: UDP, ARP, and ICMP.  A sample of these
   applications are: TELNET, FTP, and rcp.  A more accurate term is
   "internet technology".  A network that uses internet technology is
   called an "internet".

2.1  Basic Structure

   To understand this technology you must first understand the following
   logical structure:

                     ----------------------------
                     |    network applications  |
                     |                          |
                     |...  \ | /  ..  \ | /  ...|
                     |     -----      -----     |
                     |     |TCP|      |UDP|     |
                     |     -----      -----     |
                     |         \      /         |
                     |         --------         |
                     |         |  IP  |         |
                     |  -----  -*------         |
                     |  |ARP|   |               |
                     |  -----   |               |
                     |      \   |               |
                     |      ------              |
                     |      |ENET|              |
                     |      ---@--              |
                     ----------|-----------------
                               |
         ----------------------o---------
             Ethernet Cable

                  Figure 1.  Basic TCP/IP Network Node

   This is the logical structure of the layered protocols inside a
   computer on an internet.  Each computer that can communicate using
   internet technology has such a logical structure.  It is this logical
   structure that determines the behavior of the computer on the
   internet.  The boxes represent processing of the data as it passes
   through the computer, and the lines connecting boxes show the path of

Socolofsky & Kale                                               [Page 2]
RFC 1180                   A TCP/IP Tutorial                January 1991

   data.  The horizontal line at the bottom represents the Ethernet
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