September 1981 
                                                       Internet Protocol
                                                                Overview



    datagram.  The more-fragments flag is set to one.  The second
    portion of the data is placed in the second new internet datagram,
    and the total length field is set to the length of the second
    datagram.  The more-fragments flag carries the same value as the
    long datagram.  The fragment offset field of the second new internet
    datagram is set to the value of that field in the long datagram plus
    NFB.

    This procedure can be generalized for an n-way split, rather than
    the two-way split described.

    To assemble the fragments of an internet datagram, an internet
    protocol module (for example at a destination host) combines
    internet datagrams that all have the same value for the four fields:
    identification, source, destination, and protocol.  The combination
    is done by placing the data portion of each fragment in the relative
    position indicated by the fragment offset in that fragment's
    internet header.  The first fragment will have the fragment offset
    zero, and the last fragment will have the more-fragments flag reset
    to zero.

2.4.  Gateways

  Gateways implement internet protocol to forward datagrams between
  networks.  Gateways also implement the Gateway to Gateway Protocol
  (GGP) [7] to coordinate routing and other internet control
  information.

  In a gateway the higher level protocols need not be implemented and
  the GGP functions are added to the IP module.

                                    
                   +-------------------------------+   
                   | Internet Protocol & ICMP & GGP|   
                   +-------------------------------+   
                           |                 |         
                 +---------------+   +---------------+ 
                 |   Local Net   |   |   Local Net   | 
                 +---------------+   +---------------+ 

                           Gateway Protocols

                               Figure 3.

  






 

                                                          September 1981
Internet Protocol