[clug] Diagnosing SSH performance problems [SEC=UNCLASSIFIED]

Tomasz Ciolek tmc at vandradlabs.com.au
Thu Dec 10 12:20:28 MST 2009

Hi there Antti
On Thu, Dec 10, 2009 at 05:18:44PM +1100, Roppola, Antti - BRS wrote:
> Hi all,
> So I have an SSH problem where pushing data over an SSH connation gets
> me less than 9600 baud and numerous halts and timeouts. Pulling from the
> same host just rips along as you'd expect.

In this case, for "push" you mean something like: 

rsync -avz -e ssh <client path> <server path> 

and for pull:  rsync -avz -e ssh <server path> <client path> 

> Nothing obvious seen using "ssh -v". Nothing relevant leaps out at me in
> sshd_config.
> To me this suggests the issue is deeper down in the transport, network,
> data link of physical layer. Viz, I can't think of anything in OpenSSH
> that could be mis-configured to give asymmetric symptoms.
> Does this seem like a reasonable hypothesis?

Your assumption is a safe one.

I have seen a few things cause this issue:

1. MTU settings on the server or the client. I think Michael Cohen
mentioned that already...

2. Duplex and speed mismatches on the interfaces along the path. Most
likely its something between the server and its switches where one
assumes is 100mb full and the other 100mb 1/2 or similar.

3. Miscofigured AntiVirus on the server 

Tomasz M. Ciolek	
 tmc at vandradlabs dot com dot au 
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