rfc1122.txt

bind 9.3结合mysql数据库

Network Working Group                    Internet Engineering Task Force
Request for Comments: 1122                             R. Braden, Editor
                                                            October 1989


        Requirements for Internet Hosts -- Communication Layers


Status of This Memo

   This RFC is an official specification for the Internet community.  It
   incorporates by reference, amends, corrects, and supplements the
   primary protocol standards documents relating to hosts.  Distribution
   of this document is unlimited.

Summary

   This is one RFC of a pair that defines and discusses the requirements
   for Internet host software.  This RFC covers the communications
   protocol layers: link layer, IP layer, and transport layer; its
   companion RFC-1123 covers the application and support protocols.



                           Table of Contents




   1.  INTRODUCTION ...............................................    5
      1.1  The Internet Architecture ..............................    6
         1.1.1  Internet Hosts ....................................    6
         1.1.2  Architectural Assumptions .........................    7
         1.1.3  Internet Protocol Suite ...........................    8
         1.1.4  Embedded Gateway Code .............................   10
      1.2  General Considerations .................................   12
         1.2.1  Continuing Internet Evolution .....................   12
         1.2.2  Robustness Principle ..............................   12
         1.2.3  Error Logging .....................................   13
         1.2.4  Configuration .....................................   14
      1.3  Reading this Document ..................................   15
         1.3.1  Organization ......................................   15
         1.3.2  Requirements ......................................   16
         1.3.3  Terminology .......................................   17
      1.4  Acknowledgments ........................................   20

   2. LINK LAYER ..................................................   21
      2.1  INTRODUCTION ...........................................   21



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      2.2  PROTOCOL WALK-THROUGH ..................................   21
      2.3  SPECIFIC ISSUES ........................................   21
         2.3.1  Trailer Protocol Negotiation ......................   21
         2.3.2  Address Resolution Protocol -- ARP ................   22
            2.3.2.1  ARP Cache Validation .........................   22
            2.3.2.2  ARP Packet Queue .............................   24
         2.3.3  Ethernet and IEEE 802 Encapsulation ...............   24
      2.4  LINK/INTERNET LAYER INTERFACE ..........................   25
      2.5  LINK LAYER REQUIREMENTS SUMMARY ........................   26

   3. INTERNET LAYER PROTOCOLS ....................................   27
      3.1 INTRODUCTION ............................................   27
      3.2  PROTOCOL WALK-THROUGH ..................................   29
         3.2.1 Internet Protocol -- IP ............................   29
            3.2.1.1  Version Number ...............................   29
            3.2.1.2  Checksum .....................................   29
            3.2.1.3  Addressing ...................................   29
            3.2.1.4  Fragmentation and Reassembly .................   32
            3.2.1.5  Identification ...............................   32
            3.2.1.6  Type-of-Service ..............................   33
            3.2.1.7  Time-to-Live .................................   34
            3.2.1.8  Options ......................................   35
         3.2.2 Internet Control Message Protocol -- ICMP ..........   38
            3.2.2.1  Destination Unreachable ......................   39
            3.2.2.2  Redirect .....................................   40
            3.2.2.3  Source Quench ................................   41
            3.2.2.4  Time Exceeded ................................   41
            3.2.2.5  Parameter Problem ............................   42
            3.2.2.6  Echo Request/Reply ...........................   42
            3.2.2.7  Information Request/Reply ....................   43
            3.2.2.8  Timestamp and Timestamp Reply ................   43
            3.2.2.9  Address Mask Request/Reply ...................   45
         3.2.3  Internet Group Management Protocol IGMP ...........   47
      3.3  SPECIFIC ISSUES ........................................   47
         3.3.1  Routing Outbound Datagrams ........................   47
            3.3.1.1  Local/Remote Decision ........................   47
            3.3.1.2  Gateway Selection ............................   48
            3.3.1.3  Route Cache ..................................   49
            3.3.1.4  Dead Gateway Detection .......................   51
            3.3.1.5  New Gateway Selection ........................   55
            3.3.1.6  Initialization ...............................   56
         3.3.2  Reassembly ........................................   56
         3.3.3  Fragmentation .....................................   58
         3.3.4  Local Multihoming .................................   60
            3.3.4.1  Introduction .................................   60
            3.3.4.2  Multihoming Requirements .....................   61
            3.3.4.3  Choosing a Source Address ....................   64
         3.3.5  Source Route Forwarding ...........................   65



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         3.3.6  Broadcasts ........................................   66
         3.3.7  IP Multicasting ...................................   67
         3.3.8  Error Reporting ...................................   69
      3.4  INTERNET/TRANSPORT LAYER INTERFACE .....................   69
      3.5  INTERNET LAYER REQUIREMENTS SUMMARY ....................   72

   4. TRANSPORT PROTOCOLS .........................................   77
      4.1  USER DATAGRAM PROTOCOL -- UDP ..........................   77
         4.1.1  INTRODUCTION ......................................   77
         4.1.2  PROTOCOL WALK-THROUGH .............................   77
         4.1.3  SPECIFIC ISSUES ...................................   77
            4.1.3.1  Ports ........................................   77
            4.1.3.2  IP Options ...................................   77
            4.1.3.3  ICMP Messages ................................   78
            4.1.3.4  UDP Checksums ................................   78
            4.1.3.5  UDP Multihoming ..............................   79
            4.1.3.6  Invalid Addresses ............................   79
         4.1.4  UDP/APPLICATION LAYER INTERFACE ...................   79
         4.1.5  UDP REQUIREMENTS SUMMARY ..........................   80
      4.2  TRANSMISSION CONTROL PROTOCOL -- TCP ...................   82
         4.2.1  INTRODUCTION ......................................   82
         4.2.2  PROTOCOL WALK-THROUGH .............................   82
            4.2.2.1  Well-Known Ports .............................   82
            4.2.2.2  Use of Push ..................................   82
            4.2.2.3  Window Size ..................................   83
            4.2.2.4  Urgent Pointer ...............................   84
            4.2.2.5  TCP Options ..................................   85
            4.2.2.6  Maximum Segment Size Option ..................   85
            4.2.2.7  TCP Checksum .................................   86
            4.2.2.8  TCP Connection State Diagram .................   86
            4.2.2.9  Initial Sequence Number Selection ............   87
            4.2.2.10  Simultaneous Open Attempts ..................   87
            4.2.2.11  Recovery from Old Duplicate SYN .............   87
            4.2.2.12  RST Segment .................................   87
            4.2.2.13  Closing a Connection ........................   87
            4.2.2.14  Data Communication ..........................   89
            4.2.2.15  Retransmission Timeout ......................   90
            4.2.2.16  Managing the Window .........................   91
            4.2.2.17  Probing Zero Windows ........................   92
            4.2.2.18  Passive OPEN Calls ..........................   92
            4.2.2.19  Time to Live ................................   93
            4.2.2.20  Event Processing ............................   93
            4.2.2.21  Acknowledging Queued Segments ...............   94
         4.2.3  SPECIFIC ISSUES ...................................   95
            4.2.3.1  Retransmission Timeout Calculation ...........   95
            4.2.3.2  When to Send an ACK Segment ..................   96
            4.2.3.3  When to Send a Window Update .................   97
            4.2.3.4  When to Send Data ............................   98



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            4.2.3.5  TCP Connection Failures ......................  100
            4.2.3.6  TCP Keep-Alives ..............................  101
            4.2.3.7  TCP Multihoming ..............................  103
            4.2.3.8  IP Options ...................................  103
            4.2.3.9  ICMP Messages ................................  103
            4.2.3.10  Remote Address Validation ...................  104
            4.2.3.11  TCP Traffic Patterns ........................  104
            4.2.3.12  Efficiency ..................................  105
         4.2.4  TCP/APPLICATION LAYER INTERFACE ...................  106
            4.2.4.1  Asynchronous Reports .........................  106
            4.2.4.2  Type-of-Service ..............................  107
            4.2.4.3  Flush Call ...................................  107
            4.2.4.4  Multihoming ..................................  108
         4.2.5  TCP REQUIREMENT SUMMARY ...........................  108

   5.  REFERENCES .................................................  112



































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RFC1122                       INTRODUCTION                  October 1989


1.  INTRODUCTION

   This document is one of a pair that defines and discusses the
   requirements for host system implementations of the Internet protocol
   suite.  This RFC covers the communication protocol layers:  link
   layer, IP layer, and transport layer.  Its companion RFC,
   "Requirements for Internet Hosts -- Application and Support"
   [INTRO:1], covers the application layer protocols.  This document
   should also be read in conjunction with "Requirements for Internet
   Gateways" [INTRO:2].

   These documents are intended to provide guidance for vendors,
   implementors, and users of Internet communication software.  They
   represent the consensus of a large body of technical experience and
   wisdom, contributed by the members of the Internet research and
   vendor communities.

   This RFC enumerates standard protocols that a host connected to the
   Internet must use, and it incorporates by reference the RFCs and
   other documents describing the current specifications for these
   protocols.  It corrects errors in the referenced documents and adds
   additional discussion and guidance for an implementor.

   For each protocol, this document also contains an explicit set of
   requirements, recommendations, and options.  The reader must
   understand that the list of requirements in this document is
   incomplete by itself; the complete set of requirements for an
   Internet host is primarily defined in the standard protocol
   specification documents, with the corrections, amendments, and
   supplements contained in this RFC.

   A good-faith implementation of the protocols that was produced after
   careful reading of the RFC's and with some interaction with the
   Internet technical community, and that followed good communications
   software engineering practices, should differ from the requirements
   of this document in only minor ways.  Thus, in many cases, the
   "requirements" in this RFC are already stated or implied in the
   standard protocol documents, so that their inclusion here is, in a
   sense, redundant.  However, they were included because some past
   implementation has made the wrong choice, causing problems of
   interoperability, performance, and/or robustness.

   This document includes discussion and explanation of many of the
   requirements and recommendations.  A simple list of requirements
   would be dangerous, because:

   o    Some required features are more important than others, and some
        features are optional.



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RFC1122                       INTRODUCTION                  October 1989


   o    There may be valid reasons why particular vendor products that