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Re: ssh tunnel problems



On Sun, 2008-06-22 at 17:36 +0930, Tim wrote:
> On Sat, 2008-06-21 at 19:34 -0400, Rick Bilonick wrote:
> > What on the work server could be preventing the reverse tunnel from
> > working? On the server I do use hosts.allow to only allow ssh from my
> > home computer. Could this possibly prevent the reverse tunnel from
> > working? Or is the problem on my home computer?
> 
> Firewalling?  But we can only guess without detailed information about
> the network configuration, on both sides.
> 
> I would still try completely avoiding referring to localhost, anywhere.
> It's awfully confusing trying to follow your steps, and I can forsee you
> getting tangled in a knot.
> 
> -- 
> [tim localhost ~]$ uname -r
> 2.6.25.6-55.fc9.i686
> 
> Don't send private replies to my address, the mailbox is ignored.  I
> read messages from the public lists.
> 
> 
> 

How do you explain that this works fine when going from my home computer
to an account on my ISP's computer? I followed an example posted on the
web (which DID have one mistake in using "localhost" which I corrected -
but the other use of "localhost" is AFAIK correct). In order to do a
reverse tunnel, don't you have to point to localhost in order to use the
forwarded port? 

I don't see this as confusing:

(on my.work.server which is behind a firewall that blocks incoming ssh
but not outgoing ssh)

> ssh -R 2022:my.work.server:22 me home computer

where "my.work.server" is the IP address for my.work.server and
"home.computer" is the IP address for my home.computer. This sets up the
port forwarding for a reverse tunnel (that's the -R option). If on
home.computer I do:

> netstat -an | grep 2022

it shows that home.computer is listening to port 2022.

Then, to use the reverse tunnel (again on home.computer):

> ssh -p 2022 accnt localhost

where "accnt" is the user account on my.work.server and I use the
password for accnt on my.work.server. This should allow me then to go
through the ssh tunnel in the reverse direction (getting through the
firewall that is blocking the use of incoming ssh from the home computer
to the my.work.server).

Even after removing everything in hosts.allow on my.work.server, I still
can't connect.

This SAME set up works fine if I set up the tunnel from my home computer
to my account on my ISP's server. And yes I'm using "localhost" similar
to what I show above. And I've tried it from my.work.server to my
account on my ISP but have the same problem so the problem is something
on my.work.server. 

Is it possible for the firewall to block a reverse tunnel (without
blocking outgoing ssh)?

Rick B.


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