Odd TCP RFC1323 Behavior

[Bjoern A. Zeeb]

On Aug 12, 2011, at 11:36 PM, Kevin Oberman wrote:

> 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.

and let me point out that the relevant patch is in stock HEAD and will ship by default with 9.0.


> 
> 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
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-- 
Bjoern A. Zeeb                                 You have to have visions!
         Stop bit received. Insert coin for new address family.