Hello Friends @ 3000-L,

Re: TCP/IP & IP "Precedence" bit.

I have run into an interesting case where the 3000 sends a RESET and
clears the TCP connection when a client increases the precedence in an
IP packet sent to the 3000 NS-TRANSPORT.

I have always believed it was illegal (against TCP/IP RFC specification)
to change the precedence in an IP packet once the precedence has been
negotiated in the 3-way TCP connection establishment SYN -> SYN/ACK -> ACK.

I back this up with RFC 793 which say's:

+-------------------------------------------------------------RFC-793--+
                                                               [Page 67]
                                                            January 1980
Transmission Control ProtocolFunctional Specification
                                                         SEGMENT ARRIVES
    second check security and precedence
      If the security/compartment and precedence in the segment do not
      exactly match the security/compartment and precedence in the TCB
      then form a reset and return.
      Note this check is placed following the sequence check to prevent
      a segment from an old connection between these parts with a
      different security or precedence from causing an abort of the
      current connection.
+-------------------------------------------------------------RFC-793--+

  My understanding of this RFC is the state SEGMENT ARRIVES is achieved
following the 3-way TCP connection establishment SYN -> SYN/ACK -> ACK
and that changing the precedence in this state will result in a RESET
packet sent in reply to the received packet and the local TCP connection
is closed.

  I have reviewed more recent RFC's for TCP/IP, also Comer's INTERNETWORKING
WITH TCP/IP (Volume I) Third Edition and Wright and "Stevens" TCP/IP
Illustrated, Volume 1 & Volume 2 and I have not found a document which
overrides the RFC 793...

  I would appreciate any input from my esteemed colleagues out here on the
3000-L news group, especially if you can find a document which overrides
or changes my understanding of the above RFC 793.

Regards,

James Hofmeister
Hewlett Packard
Worldwide Technology Network Expert Center
P.S. My Ideals are my own, not necessarily my employers.