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Date:      Sun, 14 Nov 2021 18:41:16 +0100
From:      Kurt Jaeger <pi@freebsd.org>
To:        "Andrey V. Elsukov" <bu7cher@yandex.ru>
Cc:        tuexen@freebsd.org, freebsd-net@freebsd.org
Subject:   Re: dtrace to trace incoming connection not suceeding ?
Message-ID:  <YZFKPIEROC1cwcOQ@fc.opsec.eu>
In-Reply-To: <eec5880e-3164-f0a2-3748-687098de3026@yandex.ru>
References:  <YY5nhomjYRnRojwa-v2@fc.opsec.eu> <866D4765-25EF-4C5F-AA2E-D6BE8D5EBEEB@freebsd.org> <YY6C2/OyG3KTvV%2BM@fc.opsec.eu> <43FC040E-E5DE-4F4E-B91E-AAA807207D05@freebsd.org> <YY6ITiq%2B8x5nw5a/@fc.opsec.eu> <36CCF1D0-34EE-4E1C-B593-71CF936F4DE7@freebsd.org> <YY6k1JzP4EbKCF7m@fc.opsec.eu> <eec5880e-3164-f0a2-3748-687098de3026@yandex.ru>

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Hi!

> > There's one small diff between the two that I do not understand:
> > 
> > -       18040 times no signature provided by segment
> > +       18045 times no signature provided by segment
> 
> This means, that received TCP segment has not TCP-MD5 signature, but
> listen socket expects it. Such SYN segment will be dropped by syncache
> code. Probably your BGP daemon configured to use TCP-MD5 for connection,
> but remote side does not.

Thanks, that might be another possible cause.

This happened on iBGP sessions where I control both sides
or on eBGP sessions, where I also control both sides (and both
run on FreeBSD). I did not change the frr config during updates,
so I did not expect this to break.

Maybe frr on newer FreeBSD versions handles the tcp-md5 case in some
invalid way. That might be the case and this probably needs to
be analysed.

-- 
pi@FreeBSD.org         +49 171 3101372                  Now what ?



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