Tuesday, September 04, 2007

SSH reverse tunnel

# ssh -nNT -R

The "-n" option prevents reading from STDIN. Redirection from /dev/null to STDIN.
"-N" tells ssh that the tunnel is not for executing remote commands.
"-T" tells ssh not to allocate a pseudo-tty on the remote system.
"-T" disables pseudo-tty allocation.

Rough diagram: <---

To avoid timeout:

In /etc/ssh/sshd_config on the server:
TCPKeepAlive yes
ClientAliveInterval 30
ClientAliveCountMax 99999

To enable binding address in ssh -R:
GatewayPorts yes

Man page docu for -R switch:
-R [bind_address:]port:host:hostport

Specifies that the given port on the remote (server) host is to be forwarded to the given host and port on the local side. This works by allocating a socket to listen to port on the remote side, and whenever a connection is made to this port, the connection is forwarded over the secure channel, and a connection is made to host port hostport from the local machine.

Port forwardings can also be specified in the configuration file. Privileged ports can be forwarded only when logging in as root on the remote machine. IPv6 addresses can be specified by enclosing the address in square braces or using an alternative syntax: [bind_address/]host/port/hostport.

By default, the listening socket on the server will be bound to the loopback interface only. This may be overriden by specifying a bind_address. An empty bind_address, or the address "*", indicates that the remote socket should listen on all interfaces. Specifying a remote bind_address will only succeed if the serverâs GatewayPorts option is enabled (see sshd_config(5)).

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