From owner-freebsd-hackers  Tue Feb  4 18:34:28 1997
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To: "Brian Somers" <brian@utell.co.uk>
cc: "Charles Mott" <cmott@srv.net>, "Julian Elischer" <julian@whistle.com>,
        "Eivind Eklund" <eivind@dimaga.com>,
        "Ari Suutari" <ari.suutari@ps.carel.fi>, hackers@freebsd.org
Subject: Re: Single socket version of natd 
In-reply-to: Your message of "Tue, 04 Feb 1997 18:37:30 GMT."
             <199702041837.SAA02367@ui-gate.utell.co.uk> 
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Date: Wed, 05 Feb 1997 01:49:00 +0000
From: Brian Somers <brian@awfulhak.demon.co.uk>
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> I don't know specifically without checking the code, but I recall seeing a
> comment in the -current sources (I've just checked SNAP-961014, nothing
> about it there) about using the ip_sum to differentiate between incoming
> and outgoing packets.....  It *WAS* commented as being a HACK :(
> 
> I'll check the code out this evening when I get home (-current machine)
> and tell you.
[.....]

I was lying.  There's no such comments !

Does anyone know of a reason (besides the divert(4) man page) that the
sum on incoming packets is zero'd ?
The code says:

[.....]
        if (hlen == sizeof(struct ip)) {
                ip->ip_sum = in_cksum_hdr(ip);
        } else {
                ip->ip_sum = in_cksum(m, hlen);
        }
        if (ip->ip_sum) {
                ipstat.ips_badsum++;
                goto bad;
        }
[.....]

Is there any problems with changing this to

        u_short sum;
.....
        if (hlen == sizeof(struct ip)) {
                sum = in_cksum_hdr(ip);
        } else {
                sum = in_cksum(m, hlen);
        }
        if (sum) {
                ipstat.ips_badsum++;
                goto bad;
        }

(and updating divert(4)) ?
-- 
Brian <brian@awfulhak.demon.co.uk>, <brian@freebsd.org>
      <http://www.awfulhak.demon.co.uk/>
Don't _EVER_ lose your sense of humour....