Subject: Re: UDP checksums
To: None <>
From: Mike Long <>
List: current-users
Date: 03/09/1994 18:51:00
>From: "Chris G. Demetriou" <>
>Date: Wed, 09 Mar 94 14:48:04 -0800

>i think you've confused "COMPAT_42", "COMPAT_43", and "TCP_COMPAT_42".
>The latter two are defined in the standard config files.
>I've *never* seen the former defined under NetBSD, so you *do* get
>UDP checksumming.

I found descriptions for two of these options in
/usr/src/share/doc/smm/02.config/e.t (beware, it's almost certainly
*significantly* out of date), which describes COMPAT_42 and
TCP_COMPAT_42 thusly:


This option forces the system to limit its initial TCP sequence numbers
to positive numbers.
Without this option, 4.3BSD systems may have problems with TCP connections
to 4.2BSD systems that connect but never transfer data.
The problem is a bug in the 4.2BSD TCP; this option should be used
during the period of conversion to 4.3BSD.


This option, intended as a catchall for 4.2BSD compatibility options,
has only a single function thus far.
It disables the checking of UDP input packet checksums.
As the calculation of UDP packet checksums was incorrect in 4.2BSD,
this option allows a 4.3BSD system to receive UDP packets from
a 4.2BSD system.

I don't see why you'd want one and not the other.  How many
uncorrected 4.2BSD systems still exist?
Mike Long                               
VLSI Design Engineer                              voice: (617)461-4030
Analog Devices, SPD Div.                            FAX: (617)461-3010
Norwood, MA 02062                            *this = !opinion(Analog);