I try to establish a remote ssh connection. I tried to connect Remote with ssh -fN -R 10110:localhost:22 GatewayUser@GatewayHostand Gateway with ssh -p10110 RemoteUser@localhostI got the response on the Gateway Console Connection closed by ::1running it with -v ssh -v -fN -R 10110:localhost:22 GatewayUser@GatewayHostproduces that response in the Remote-Consoledebug1: client_input_global_request: rtype keepalive@openssh.com want_reply 1debug1: client_input_global_request: rtype keepalive@openssh.com want_reply 1debug1: client_input_channel_open: ctype forwarded-tcpip rchan 2 win 2097152 max 32768debug1: client_request_forwarded_tcpip: listen localhost port 10110, originator ::1 port 48481debug1: connect_next: host localhost ([127.0.0.1]:22) in progress, fd=4debug1: channel 0: new [::1]debug1: confirm forwarded-tcpipdebug1: channel 0: connected to localhost port 22debug1: channel 0: free: ::1, nchannels 1debug1: client_input_global_request: rtype keepalive@openssh.com want_reply 1debug1: client_input_global_request: rtype keepalive@openssh.com want_reply 1PS: a SSH connection from Remote to Gateway is workingMany thanks in advance!__Here the console-output when connecting from the gateway machineemanuel@UbuntuServer:~$ ssh -vvv -p10110 pi@localhostOpenSSH_6.7p1 Ubuntu-5ubuntu1.3, OpenSSL 1.0.1f 6 Jan 2014debug1: Reading configuration data /etc/ssh/ssh_configdebug1: /etc/ssh/ssh_config line 19: Applying options for *debug2: ssh_connect: needpriv 0debug1: Connecting to localhost [::1] port 10110.debug1: Connection established.debug1: key_load_public: No such file or directorydebug1: identity file /home/emanuel/.ssh/id_rsa type -1debug1: key_load_public: No such file or directorydebug1: identity file /home/emanuel/.ssh/id_rsa-cert type -1debug1: key_load_public: No such file or directorydebug1: identity file /home/emanuel/.ssh/id_dsa type -1debug1: key_load_public: No such file or directorydebug1: identity file /home/emanuel/.ssh/id_dsa-cert type -1debug1: key_load_public: No such file or directorydebug1: identity file /home/emanuel/.ssh/id_ecdsa type -1debug1: key_load_public: No such file or directorydebug1: identity file /home/emanuel/.ssh/id_ecdsa-cert type -1debug1: key_load_public: No such file or directorydebug1: identity file /home/emanuel/.ssh/id_ed25519 type -1debug1: key_load_public: No such file or directorydebug1: identity file /home/emanuel/.ssh/id_ed25519-cert type -1debug1: Enabling compatibility mode for protocol 2.0debug1: Local version string SSH-2.0-OpenSSH_6.7p1 Ubuntu-5ubuntu1.3debug1: Remote protocol version 2.0, remote software version OpenSSH_6.0p1 Debian-4+deb7u2debug1: match: OpenSSH_6.0p1 Debian-4+deb7u2 pat OpenSSH* compat 0x04000000debug2: fd 3 setting O_NONBLOCKdebug3: put_host_port: [localhost]:10110debug3: load_hostkeys: loading entries for host [localhost]:10110 from file /home/emanuel/.ssh/known_hostsdebug3: load_hostkeys: loaded 0 keysdebug1: SSH2_MSG_KEXINIT sentConnection closed by ::1emanuel@UbuntuServer:~$ 
Reverse SSH Connection closed by ::1
ssh;ssh tunneling;openssh
What you do is: Crate a ssh connection from the raspi to the gateway, and forward the  *:10110 from the gateway to 127.0.0.1:22 on the raspi. Then you connect to port 10110@localhost, which may in some configurations use the ip6-address (::1) which has no tunnel behind it. sshd then closes the connection.Try ssh -4 -p10110 pi@localhostThis should get you one step further.If you have problems finding the correct key (ssh stops after a certain amount of checked keys) then disable pubkeyauth with ssh -oPubkeyAuthentication=no -4 -p10110 pi@localhost