Date: Fri, 12 Aug 2011 16:36:47 -0700 From: Kevin Oberman <kob6558@gmail.com> To: chip@2bithacker.net, freebsd-net@freebsd.org Subject: Re: Odd TCP RFC1323 Behavior Message-ID: <CAN6yY1s9nG5Q9AeVQiXm8mRgr3FELTPDTq9CVkWjpTxHx1Q-Eg@mail.gmail.com> In-Reply-To: <20110812214309.GI72508@2bithacker.net> References: <20110812214309.GI72508@2bithacker.net>
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On Fri, Aug 12, 2011 at 2:43 PM, Chip Marshall <chip@2bithacker.net> wrote: > I've been digging into an issue with SSH throughput and > discovered that one of the servers involved isn't using RFC1323 > window scaling and timestamps. > > The server is running 7.3-RELEASE-p3, and has > net.inet.tcp.rfc1323 set to 1. > > When connecting out from the server, it sets both Window Scale > and TimeStamp options in the SYN packet and everything is fine. > > When a connection comes into the server with WS and TS set in > the SYN, the response varies. For port 53 (named) the SYN/ACK > has WS/TS options. For port 22 (sshd) the SYN/ACK does not have > WS/TS options, unless the connection is via lo0. > > ssh is OpenSSH_5.2p1, compiled from ports with default options. > > I'm really at a loss to explain this. > > Why does named use RFC1323 on bce0 when sshd doesn't? > Why does sshd use RFC1323 on lo0 but not on bce0? > > I can provide PCAPs of the SYN, SYN/ACK exchanges if that > will help. Try installing security/openssh-portable from ports and enable the HPN patches. As it stands today, openssh locks the window size to a tiny value. This causes performance over wide area links to be simply terrible. Take a look at http://fasterdata.es.net/fasterdata/say-no-to-scp/ for more information on the issue. As you will see there, window scaling is the least of the performance issues with openssh. -- R. Kevin Oberman, Network Engineer - Retired E-mail: kob6558@gmail.com
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