Date: Thu, 14 Sep 2006 13:30:06 +0400 From: Ruslan Ermilov <ru@FreeBSD.org> To: Andre Oppermann <andre@FreeBSD.org> Cc: freebsd-net@FreeBSD.org, Igor Sysoev <is@rambler-co.ru>, silby@FreeBSD.org Subject: Re: Improved TCP syncookie implementation Message-ID: <20060914093006.GE26261@rambler-co.ru> In-Reply-To: <45086AAF.108@freebsd.org> References: <44FAE332.4010209@freebsd.org> <20060913190241.S13138@is.park.rambler.ru> <45085472.5040903@freebsd.org> <20060913230748.P14337@is.park.rambler.ru> <45086AAF.108@freebsd.org>
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--ZwgA9U+XZDXt4+m+ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Sep 13, 2006 at 10:31:43PM +0200, Andre Oppermann wrote: > Igor Sysoev wrote: > >Well, suppose protocol similar to SSH or SMTP: > > > >1) the client calls connect(), it sends SYN; > >2) the server receives SYN and sends SYN/ACK with cookie; > >3) the client receives SYN/ACK and sends ACK; > >4) the client returns successfully from connect() and calls read(); > >5) the ACK is lost; > >6) the server does not about this connection, so application can not > > accept() it, and it can not send() HELO message. > >7) the client gets ETIMEDOUT from read(). > > > >Where in this sequence client may retransmit its ACK ? >=20 > Never. You're correct. There is no data that would cause a retransmit > if the application is waiting for a server prompt first. I shouldn't > write wrong explanations when I'm tired, hungry and in between two tasks.= ;) >=20 > This problem is the reason why we don't switch entirely to syncookies > and still keep syncache as is. >=20 Perhaps it would be a good idea to remove net.inet.tcp.syncookies_only then? In any case, please don't forget to update the syncache(4) manpage to reflect your changes, and if you decide not to remove this sysctl, please add a warning of its potential to break a protocol. Cheers, --=20 Ruslan Ermilov ru@FreeBSD.org FreeBSD committer --ZwgA9U+XZDXt4+m+ Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.5 (FreeBSD) iD8DBQFFCSEeqRfpzJluFF4RAts1AJ9RMcvus0lo8ag4/X41W1+gSip2jQCZAU+9 QuQJsMytIv7ja4rzuOEY8XY= =4K+D -----END PGP SIGNATURE----- --ZwgA9U+XZDXt4+m+--
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