ssh tunnel problems
rab at nauticom.net
Tue Jun 24 04:35:08 UTC 2008
On Mon, 2008-06-23 at 16:35 -0500, Kevin Martin wrote:
> > 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 at 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 at 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.
> What do you see if you add -v to the "ssh -p 2022 accnt at localhost"?
> Also, what if you, instead of using localhost, use the ip address of
> your eth0 interface in the previous command? If you do that and, in
> another terminal, do a "tcpdump -i eth0 -vv -l port 2022" do you see
> the connection attempt being made to the port? Also try adding -v to
> the connection where you are creating the tunnel and then watch the
> output of that connection as you try to make a connection back over
> the tunnel.
> FWIW, I just did your exact setup with two machines that I have and it
> worked perfectly (prompted me for passwords and then the logins
> worked). I added -v to both the tunnel creation and then the reverse
> use of the tunnel and saw some fun stuff.
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I will try this tomorrow and capture the results. I have done this but
haven't had time to document everything. Thanks.
I did try replacing localhost with the IP address of the computer but,
if memory serves, nothing happens (no message, no connection). I also
turned off portsentry but it did not fix things.
I'm going to use my F8 laptop to replace the server temporarily and see
if it works with the laptop.
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