slow ssh connections on LAN

[Derek Atkins]

dsr at tao.merseine.nu writes:

> On Mon, Jul 10, 2006 at 10:40:26PM -0400, Robert La Ferla wrote:
>> 
>> What kind of throughput is typically of a "scp" on a 100BaseT LAN?
>> 
>> ssh is encrypting the data, but is that really slowing the transfer  
>> rate down?  The encryption algorithm does add overhead to the amount  
>> of data to be transferred and it surely slows down the CPU.  This  
>> will affect the final transfer time but shouldn't affect the transfer  
>> rate much.
>
> On any close-to-modern CPUs with files larger than a few megabytes apiece,
> you should be able to get full wire speed -- SCP should report
> something near 9-10 MB/s.

I regularly see scp reporting 10-11MB/s across my 100BaseT.  For example:

1041_20060709205900_20060709220100.nuv        100% 3484MB  10.8MB/s   05:23

>> What tools can I use to diagnose network performance issues (other  
>> than ping)?  Ethereal?
>
> You can test end-to-end bandwidth with httperf, iperf,
> pathchar... take a look at
> http://www.caida.org/tools/taxonomy/perftaxonomy.xml

Check your MTU..  Do the test with smaller MTUs.  You might have a
bad/broken switch/hub.  I had a problem where machine on one side of a
switch were fine but hosts on the other side of the switch were not...
I.e., anytime it crossed the switch it had problems (unless I reduced
my MTU to something like 1200).  I replaced that switch and it's been
working great since.

> -dsr-

-derek

-- 
       Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
       Member, MIT Student Information Processing Board  (SIPB)
       URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
       warlord at MIT.EDU                        PGP key available