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SSH Tunnel Static (Fixed-Destination) Port Forwarding

Demonstrates fixed-destination port forwarding with the DestHostname, DestPort, ListenBindIpAddress, and ListenPort properties. Every local connection accepted by the listener is forwarded to the same fixed destination through the SSH server.

Background: This is the classic ssh -L scenario: expose a single remote service — a database, an internal web app — at a local port. Binding the listener to 127.0.0.1 keeps the tunnel private to the local machine, whereas 0.0.0.0 would let other hosts route through it. Passing 0 to BeginAccepting lets the OS pick a free port, which ListenPort then reports — handy when a fixed port might already be in use.

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Add-Type -Path "C:\chilkat\ChilkatDotNet47-x64\ChilkatDotNet47.dll"

$success = $false

#  Demonstrates fixed-destination (static) port forwarding with the SshTunnel properties
#  DestHostname, DestPort, ListenBindIpAddress, and ListenPort.
#  
#  Every local connection accepted by the listener is forwarded to the same fixed destination
#  through the SSH server.

$tunnel = New-Object Chilkat.SshTunnel

#  The fixed destination that accepted connections are forwarded to.
$tunnel.DestHostname = "db.internal.example.com"
$tunnel.DestPort = 5432

#  Bind the listener to loopback so only local processes can use the tunnel.  Use "0.0.0.0" to
#  accept connections from other machines (less secure).
$tunnel.ListenBindIpAddress = "127.0.0.1"

$sshPort = 22
$success = $tunnel.Connect("ssh.example.com",$sshPort)
if ($success -eq $false) {
    $($tunnel.LastErrorText)
    exit
}

#  Normally you would not hard-code the password in source.  You should instead obtain it
#  from an interactive prompt, environment variable, or a secrets vault.
$password = "mySshPassword"

$success = $tunnel.AuthenticatePw("mySshLogin",$password)
if ($success -eq $false) {
    $($tunnel.LastErrorText)
    exit
}

#  Pass 0 to let the operating system choose an available port.  After BeginAccepting succeeds,
#  ListenPort contains the actual port that was bound.
$success = $tunnel.BeginAccepting(0)
if ($success -eq $false) {
    $($tunnel.LastErrorText)
    exit
}

$("Listening on 127.0.0.1 port " + $tunnel.ListenPort)

#  Applications now connect to 127.0.0.1:ListenPort as if it were the database server.

$waitForThreadExit = $true
$success = $tunnel.CloseTunnel($waitForThreadExit)
if ($success -eq $false) {
    $($tunnel.LastErrorText)
    exit
}