If the address in destination address field has been reached and
        the pointer is not greater than the length, the next address in
        the source route replaces the address in the destination address
        field, and the recorded route address replaces the source
        address just used, and pointer is increased by four.

        The recorded route address is the internet module's own internet
        address as known in the environment into which this datagram is
        being forwarded.

        This procedure of replacing the source route with the recorded
        route (though it is in the reverse of the order it must be in to
        be used as a source route) means the option (and the IP header
        as a whole) remains a constant length as the datagram progresses
        through the internet.

        This option is a loose source route because the gateway or host
        IP is allowed to use any route of any number of other
        intermediate gateways to reach the next address in the route.

        Must be copied on fragmentation.  Appears at most once in a
        datagram.

      Strict Source and Record Route

        +--------+--------+--------+---------//--------+
        |10001001| length | pointer|     route data    |
        +--------+--------+--------+---------//--------+
         Type=137

        The strict source and record route (SSRR) option provides a
        means for the source of an internet datagram to supply routing
        information to be used by the gateways in forwarding the
        datagram to the destination, and to record the route
        information.

        The option begins with the option type code.  The second octet
        is the option length which includes the option type code and the
        length octet, the pointer octet, and length-3 octets of route
        data.  The third octet is the pointer into the route data
        indicating the octet which begins the next source address to be
        processed.  The pointer is relative to this option, and the
        smallest legal value for the pointer is 4.

        A route data is composed of a series of internet addresses.
        Each internet address is 32 bits or 4 octets.  If the pointer is
        greater than the length, the source route is empty (and the




 

                                                          September 1981
Internet Protocol
Specification



        recorded route full) and the routing is to be based on the
        destination address field.

        If the address in destination address field has been reached and
        the pointer is not greater than the length, the next address in
        the source route replaces the address in the destination address
        field, and the recorded route address replaces the source
        address just used, and pointer is increased by four.

        The recorded route address is the internet module's own internet
        address as known in the environment into which this datagram is
        being forwarded.

        This procedure of replacing the source route with the recorded
        route (though it is in the reverse of the order it must be in to
        be used as a source route) means the option (and the IP header
        as a whole) remains a constant length as the datagram progresses
        through the internet.

        This option is a strict source route because the gateway or host
        IP must send the datagram directly to the next address in the
        source route through only the directly connected network
        indicated in the next address to reach the next gateway or host
        specified in the route.

        Must be copied on fragmentation.  Appears at most once in a
        datagram.

      Record Route

        +--------+--------+--------+---------//--------+
        |00000111| length | pointer|     route data    |
        +--------+--------+--------+---------//--------+
          Type=7

        The record route option provides a means to record the route of
        an internet datagram.

        The option begins with the option type code.  The second octet
        is the option length which includes the option type code and the