Odd TCP RFC1323 Behavior

[Kevin Oberman]

On Fri, Aug 12, 2011 at 2:43 PM, Chip Marshall <chip at 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 at gmail.com