Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!decwrl!sgi!vjs@rhyolite.wpd.sgi.com
From: vjs@rhyolite.wpd.sgi.com (Vernon Schryver)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: SLIP documents
Summary: fooey
Message-ID: <85079@sgi.sgi.com>
Date: 12 Feb 91 17:32:51 GMT
References: <1991Feb8.203703.25654@zoo.toronto.edu> <1991Feb11.233102.24222@Think.COM>
Sender: guest@sgi.sgi.com
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 46

In article <1991Feb11.233102.24222@Think.COM>, barmar@think.com (Barry Margolin) writes:
> 
> From p.78 of RFC1122:
> 
>    An application MAY optionally be able to control whether a UDP checksum
>    will be generated, but it MUST default to checksumming on.
> 
>    If a UDP datagram is received with a checksum that is non-zero and
>    invalid, UDP MUST silently discard the datagram.
> 
> 4.2BSD-based UDP implementations violate both these requirements.  First,
> it is supposed to be the application that decides whether it wants
> checksumming; in BSD, either all applications get it or none do.  Second,
> it is not permitted to disable checking of received packets.


The important word in the first paragraph is "MAY".  1122 does not require
that an application be able to disable UDP checksumming.  4.3BSD does not
have such a switch, and does not violate 1122 by not having it.

As long as you don't break it by changing udpcksum, 4.3BSD does not violate
the second paragraph.

The fact that 4.3BSD has additional characteristics cannot rationally be
considered a violation of the standard.  If the characteristic of being
able to change to non-conforming behavior is sufficient to be non-standard,
then only ROM based systems can be standard, since there are always
bozos--err--valued customers who can, will, and do change things in ways
you and I consider obviously stupid and non-conforming.  Does the fact that
many people installed their own implementations of TCP/IP (often BSD
derived) on popular workstations by itself make those systems non-1122
compliant even when running the vendor supplied system?  If the answer to
that question were yes, then 1122 and 1123 would be uninteresting to
workstation vendors and our customers.

Please keep standards carping rational.  It appears that some common
workstations (not my employer's) violate the above quoted part of 1122.
Their "feet should be held to the fire".  You are putting out the flame
when you lump 4.3BSD checksumming behavior with theirs.


(I'm assuming you mean 4.3BSD base UDP implementations, which follow the
rules you criticize, not 4.2 BSD.)


Vernon Schryver,   vjs@sgi.com