Re: Setting and Routing on the TOS Source (SRC) and Destination (DST) Bits

["Jim Fleming" <JimFleming@ameritech.net>]

----- Original Message ----- 
From: "Antony Stone" <Antony@Soft-Solutions.co.uk>
> I think that is an extreme ( = unreasonable ) point of view.
> 
> Of the 160 bits in an IPv4 header, I really do not see how you could 
> reasonably use these 49 for routing purposes:
> 
> 16 bits - fragment identifier

      DARPA INTERNET PROGRAM
      PROTOCOL SPECIFICATION
      September 1981
      Identification

                "The choice of the Identifier for a datagram is based on the need to
                provide a way to uniquely identify the fragments of a particular
                datagram.  The protocol module assembling fragments judges fragments
                to belong to the same datagram if they have the same source,
                destination, protocol, and Identifier.  Thus, the sender must choose
                the Identifier to be unique for this source, destination pair and
                protocol for the time the datagram (or any fragment of it) could be
                alive in the internet.
                It seems then that a sending protocol module needs to keep a table
                of Identifiers, one entry for each destination it has communicated
                with in the last maximum packet lifetime for the internet.
                However, since the Identifier field allows 65,536 different values,
                some host may be able to simply use unique identifiers independent
                of destination.
                It is appropriate for some higher level protocols to choose the
                identifier. For example, TCP protocol modules may retransmit an
                identical TCP segment, and the probability for correct reception
                would be enhanced if the retransmission carried the same identifier
                as the original transmission since fragments of either datagram
                could be used to construct a correct TCP segment."