Re: ssh works, scp hangs

[Chris Boot <bootc@bootc.net>]

Matt Zagrabelny wrote:

> hello,
>
> i guess i am needing help from some ssh grand masters...
>
> scenario:
>
> two debian boxes with sshd running on both.
> ssh from A to B works
> ssh from B to A works
> scp from A to B works
> scp from B to A hangs
>
> (any place there is scp you could replace it with ssh running a command,
> ie: 'ssh machine_a date')
>
> both boxes are running sarge.
>
> i have tried the above scenario by replacing B with a number of other
> debian boxes, some running sarge, some sid. in all cases the scp to A
> hangs.
>
> so i am lead to believe that it is the sshd on box A. so i purged ssh
> and reinstalled it on box A and i get the same results. argggh.
>
> i have run both the ssh client on box B in verbose mode and the ssh
> server on box A in debug mode and cant make heads or tails of the
> output. i will attach the output in hopes that someone can analyze it
> better than i can.
>
> thanks for the hints.
>
> -matt zagrabelny
>  
Hi Matt,

I'd check you have the MTU set correctly on box A. SSH usually uses 
small packets to communicate, so you won't get any fragmentation or even 
reach your MTU limit, but as soon as you transfer a large file the 
system is very likely to do that. Not entirely sure what that involves 
to be honest, but check the output of ifconfig on your machines. If 
you're behind a DSL or PPTP or other such router, you're likely to have 
an MTU lower than the ethernet default of 1500. If machine B has an MTU 
of 1500 and machine A has a lower MTU, machine A is likely to discard 
long packets from B.

I could very well be speaking out of my a*se though!

HTH,
Chris

--
Chris Boot
bootc@bootc.net
http://www.bootc.net/