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ssh local port forwarding stopped working

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  ssh local port forwarding stopped working Gary Dale <gary@extremeground.com> - 2019-05-28 19:40 +0200
    Re: ssh local port forwarding stopped working Nicholas Geovanis <nickgeovanis@gmail.com> - 2019-05-28 20:00 +0200
    Re: ssh local port forwarding stopped working Bruce Halco <bruce@halcomp.com> - 2019-05-28 23:30 +0200

#209334 — ssh local port forwarding stopped working

I'm running Debian/Testing on an AMD64 machine.

I follow what I believe is a fairly conventional way of connecting to 
remote machines. Firstly I establish an SSH tunnel using a command like:

   ssh <remote server public IP> -L 5902:<remote workstation local IP>:5900

where the remote server public IP is that of the router (DD-WRT) with 
port 22 forwarded to the local IP of a remote Debian/Stable server. The 
remote workstation IPs are in the 192.168.1.* range. The SSH connection 
works fine.

Then I connect to localhost:5902 using a VNC viewer (tried a few).  I've 
been doing this for a decade with no significant problems.

However I haven't been able to do this since at least yesterday 
(previous remote login was a week ago. It worked). No matter which 
remote machine I try to connect to, I never get to the password prompt. 
Instead the connection attempt eventually attempt times out.

I can log onto a KVM virtual machine running on the remote server using 
the Virtual Machine Manager GUI. From there I can connect to the other 
(real) machines using the Tight VNC viewer.

Since I can connect to the remote workstations from the VM, the problem 
cannot be with their service setup. And since the problem isn't resolved 
by using a different VNC viewer from my local workstation, the problem 
can't be the VNC client. This just leaves the ssh tunnel - specifically 
the port forwarding - as the only common element.

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#209339

[Multipart message — attachments visible in raw view] — view raw

My first guess would be that port(s) 5900 and/or 5902 have been blocked.
Next possibility is that for those credentials a remote user/pwd lookup is
being done unexpectedly, the lookup needs to timeout because the
credentials are invalid. Is the ID really present locally?

On Tue, May 28, 2019, 12:38 PM Gary Dale <gary@extremeground.com> wrote:

> I'm running Debian/Testing on an AMD64 machine.
>
> I follow what I believe is a fairly conventional way of connecting to
> remote machines. Firstly I establish an SSH tunnel using a command like:
>
>    ssh <remote server public IP> -L 5902:<remote workstation local IP>:5900
>
> where the remote server public IP is that of the router (DD-WRT) with
> port 22 forwarded to the local IP of a remote Debian/Stable server. The
> remote workstation IPs are in the 192.168.1.* range. The SSH connection
> works fine.
>
> Then I connect to localhost:5902 using a VNC viewer (tried a few).  I've
> been doing this for a decade with no significant problems.
>
> However I haven't been able to do this since at least yesterday
> (previous remote login was a week ago. It worked). No matter which
> remote machine I try to connect to, I never get to the password prompt.
> Instead the connection attempt eventually attempt times out.
>
> I can log onto a KVM virtual machine running on the remote server using
> the Virtual Machine Manager GUI. From there I can connect to the other
> (real) machines using the Tight VNC viewer.
>
> Since I can connect to the remote workstations from the VM, the problem
> cannot be with their service setup. And since the problem isn't resolved
> by using a different VNC viewer from my local workstation, the problem
> can't be the VNC client. This just leaves the ssh tunnel - specifically
> the port forwarding - as the only common element.
>
>

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#209352

[Multipart message — attachments visible in raw view] — view raw

I would test port status with

    nmap -P0 -p 22 <remote server public IP>


You want the response to be "open"

Bruce

On 5/28/19 12:17 PM, Gary Dale wrote:
> I'm running Debian/Testing on an AMD64 machine.
>
> I follow what I believe is a fairly conventional way of connecting to 
> remote machines. Firstly I establish an SSH tunnel using a command like:
>
>   ssh <remote server public IP> -L 5902:<remote workstation local 
> IP>:5900
>
> where the remote server public IP is that of the router (DD-WRT) with 
> port 22 forwarded to the local IP of a remote Debian/Stable server. 
> The remote workstation IPs are in the 192.168.1.* range. The SSH 
> connection works fine.
>
> Then I connect to localhost:5902 using a VNC viewer (tried a few).  
> I've been doing this for a decade with no significant problems.
>
> However I haven't been able to do this since at least yesterday 
> (previous remote login was a week ago. It worked). No matter which 
> remote machine I try to connect to, I never get to the password 
> prompt. Instead the connection attempt eventually attempt times out.
>
> I can log onto a KVM virtual machine running on the remote server 
> using the Virtual Machine Manager GUI. From there I can connect to the 
> other (real) machines using the Tight VNC viewer.
>
> Since I can connect to the remote workstations from the VM, the 
> problem cannot be with their service setup. And since the problem 
> isn't resolved by using a different VNC viewer from my local 
> workstation, the problem can't be the VNC client. This just leaves the 
> ssh tunnel - specifically the port forwarding - as the only common 
> element.
>

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