I have an old Linux box (version 2.6.12, compiled by a colleague) behind an NAT-enabled router, that I want to access from a remote PC. There's an SSH daemon running on the box, but since there was no SSH client yet, we compiled an old Dropbear client, which works fine when creating a tunnel.I should note that the SSH daemon is running on port 55000 and that the version of the Dropbear client is v0.53.The problem arises, however, when using remote port forwarding:./dbclient -N -R myserver.com:10022:localhost:55000 me@myserver.comThis prompts me for a password, and from myserver.com, I can see the connection was successful:sudo netstat -tulpn | grep 10022tcp        0      0 xx.xx.xx.xx:10022    0.0.0.0:*               LISTEN      31512/sshd: meWhen trying to use the tunnel from my Mac or Ubuntu (OpenSSH_7.4p1, LibreSSL 2.5.0), however, not much is happening.ssh -p 10022 test@myserver.comJust hangs forever. The user 'test' exists on my Linux box. In verbose mode, I get the following:ssh -p 10022 test@myserver.com -vOpenSSH_7.4p1, LibreSSL 2.5.0debug1: Reading configuration data /Users/me/.ssh/configdebug1: Reading configuration data /etc/ssh/ssh_configdebug1: Connecting to myserver.com [xx.xx.xx.xx] port 10022.debug1: Connection established.debug1: identity file /Users/me/.ssh/id_rsa type 1debug1: key_load_public: No such file or directorydebug1: identity file /Users/me/.ssh/id_rsa-cert type -1debug1: key_load_public: No such file or directorydebug1: identity file /Users/me/.ssh/id_dsa type -1debug1: key_load_public: No such file or directorydebug1: identity file /Users/me/.ssh/id_dsa-cert type -1debug1: key_load_public: No such file or directorydebug1: identity file /Users/me/.ssh/id_ecdsa type -1debug1: key_load_public: No such file or directorydebug1: identity file /Users/me/.ssh/id_ecdsa-cert type -1debug1: key_load_public: No such file or directorydebug1: identity file /Users/me/.ssh/id_ed25519 type -1debug1: key_load_public: No such file or directorydebug1: identity file /Users/me/.ssh/id_ed25519-cert type -1debug1: Enabling compatibility mode for protocol 2.0debug1: Local version string SSH-2.0-OpenSSH_7.4My knowledge of SSH is fairly basic and remote forwarding is very new to me, so I have no idea what to try next. I've tried a Dropbear client on Ubuntu and Mac, which just hangs as well. I don't think it has a verbose mode(?). I tried the reverse, i.e. setting up remote port forwarding in Ubuntu and then connecting from the Linux box and that just works.Is it just some configuration problem? Could it be that the SSH daemon is not welcoming my connections and how could I check or fix that? Do I need an older SSH client on my PC's?Any help is greatly appreciated!EDIT: does sshd require any special configuration parameters or does this have nothing to do with sshd?
SSH to older Linux box using remote port forwarding
linux;ssh;openssh;dropbear
This will definitely not be the solution for most, but I'll post it here anyway, maybe it can help someone else in the future.The problem was that on the Linux box, the loopback interface was down by default. I'm still not sure why. I figured it out by trying to SSH to localhost, which failed. Pinging didn't work either. After bringing up the loopback, everything worked:ifconfig lo up(The name of your loopback interface might be different, it depends on your OS)I can only assume that behind the scenes, a local SSH connection is being made from the forwarding tunnel to the local SSH daemon.