[kwlug-disc] ssh and port forwarding

Richard Weait richard at weait.com
Mon Dec 15 14:13:54 EST 2008


On Mon, 2008-12-15 at 12:48 -0500, Robert P. J. Day wrote:
> i have the following scenario:
> 
>   host1  <---------->  host2  <--------->  host3
>   (ME)
> 
> i want to be able to do the following from host1:
> 
>   1) ssh directly and normally to host2 (trivial)
>   2) using host2 as a gateway, ssh from host1 to get to host3
> 
> from the perspective of host1, host2 will be visible (through a
> corporate VPN, but still visible).  host3, on the other hand, will be
> "hiding" behind host2 on a totally different and internal network, so
> i have to use someone else as a gateway -- direct ssh from host1 to
> host3 is out of the question.
> 
>   assume the normal stuff: that host1 has an ssh client, and both
> host2 and host3 are running an ssh server of some kind (probably
> dropbear, actually), and that the ssh server on host2 is set up to do
> port forwarding.
> 
>   i've seen two solutions (local and remote forwarding) that involves
> doing all the work on host1 but i'd rather not do that -- i'd rather
> keep life on host1 simple, and centralize the forwarding configuration
> at host2.  so, as i read it, the direct ssh from host1 to host2 will
> still work fine, but what do i do at host2?
> 
>   since host2 *will* be running dropbear, as i read, first, on host2,
> i'll invoke:
> 
>    # dropbear -a
> 
> so that dropbear is running in port forwarding mode.
> 
>   in addition, on host2, i'll have to run:
> 
>   # dbclient -L 1234:localhost:22 host3
> 
> does that make sense?  so i can ssh from host1 to host2 normally, but
> if i want to sh from host1 to host3, i'll invoke:
> 
>   $ ssh host2 1234
> 
> which will get me to host2, which will then forward me on to port 22
> on host3.  am i on the right path here?  thanks.

You lost me at, "i've seen two solutions (local and remote forwarding)
that involves doing all the work on host1 but i'd rather not do that"  I
believe I did what you're avoiding, by running everything from host1.
Also I used plain ssh, not dropbear.  

ssh -N -L2222:host3:22 host2 & # to set up the forward from host 2 to
host 3
then from host1 again
ssh localhost:2222 # to get to host three.  

That help at all?




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