Path: utzoo!mnetor!uunet!husc6!cmcl2!brl-adm!umd5!ames!ucbcad!ucbvax!A.ISI.EDU!Stevens
From: Stevens@A.ISI.EDU (Jim Stevens)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Pseudo-Headers & Checksumming
Message-ID: <12366049272.26.STEVENS@A.ISI.EDU>
Date: 12 Jan 88 17:37:27 GMT
References: <8801111640.AA16603@topaz.rutgers.edu>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: Rockwell International
Lines: 49


Ron, 

Sorry if I did not explain myself sufficiently.

The IP RFC 791 Receive Packet interface to Higher Level Protocols
specifies that the following information is to be made available to the
Higher Level Protocols:

RECV (BufPTR, prot, => result, src, dst, TOS, len, opt)
 
 where:

  BufPTR = buffer pointer
  prot = protocol
  result = response
    OK = datagram received ok
    Error = error in arguments
  len = length of buffer
  src = source address
  dst = destination address
  TOS = type of service (including precedence)
  opt = option data (including security/compartment information).

Now although TCP can use all of this information, in actual common use
only the prot, len, src, and dst parameters are normally used.

Note that TCP does NOT need a pseudoheader to receive this information,
rather the pseudoheader is ONLY used to verify that the most common
information passed to TCP from IP is End-to-End correct.

Thus the question(s) under consideration is(are) not whether TCP (and other
transport protocols) need the information which is passed from IP to
TCP.

Rather the questions under consideration are:

1.  Since TCP (and other transport protocols) need this information
from IP, should TCP trust the information to be correct and not have
been corrupted along the way.

2.  If TCP cannot trust IP to delivery the information 99.9999999%
correct, why does TCP only specify part of the IP information in the
pseudo-header instead of all of the passed information.


Jim Stevens

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