Let's simulate intricated tunnels using JASSH (high level scala SSH API).

In the following example, we simulate bouncing between 9 SSH hosts, using SSH tunnel intrication :
  • A:22 -> B:22 -> C:22 -> D:22 -> E:22 -> F:22 -> G:22 -> H:22 -> I:22 ; (typical case : a given host is only accessible through the previous one)
  • All "foreign" hosts become directly accessible using new ssh local ports
  • A->10022, B-> 10023, ... I->10030, so now I (and all others) are direcly accessible from local ssh client host !

    // From host/port, bring back locally remote fhost/fport to local host using tport. 
    case class Sub(host:String, port:Int, fhost:String, fport:Int, tport:Int)
    
    val intricatedPath = Iterable(
        Sub("localhost", 22,    "127.0.0.1", 22, 10022), // A 
        Sub("localhost", 10022, "127.0.0.1", 22, 10023), // B
        Sub("localhost", 10023, "127.0.0.1", 22, 10024), // C
        Sub("localhost", 10024, "127.0.0.1", 22, 10025), // D
        Sub("localhost", 10025, "127.0.0.1", 22, 10026), // E
        Sub("localhost", 10026, "127.0.0.1", 22, 10027), // F
        Sub("localhost", 10027, "127.0.0.1", 22, 10028), // G
        Sub("localhost", 10028, "127.0.0.1", 22, 10029), // H
        Sub("localhost", 10029, "127.0.0.1", 22, 10030)  // I
        )
        
    def intricate[T](path:Iterable[Sub], curSSHPort:Int=22)(proc:(SSH)=>T):T = {
      path.headOption match {
        case Some(curSub) =>
          SSH.once(curSub.host, "test", port=curSub.port) { ssh =>
            ssh.remote2Local(curSub.tport, curSub.fhost, curSub.fport)
            intricate(path.tail, curSub.tport)(proc)
          }
        case None => 
          SSH.once("localhost", "test", port=curSSHPort) { ssh =>
            proc(ssh)
          }
      }
    }
    
    // Build the intricated tunnels and execute a ssh command on the farthest host (I)
    val result = intricate(intricatedPath) {ssh =>
      ssh.executeAndTrim("echo 'Hello intricated world'")
    }

    println(result)
So now let's automate complex SSH tunnels construction, with automatic rebuild on failure and direct integration into tools, when some direct access are not possible...