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




 



RFC1122                       INTRODUCTION                  October 1989


         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




 



RFC1122                       INTRODUCTION                  October 1989


            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