Tcl

Connect an SSH Tunnel Through a Jump Host

Demonstrates the Chilkat SshTunnel.ConnectThroughSsh method, which connects to an SSH server through an already connected and authenticated Ssh object. The first argument is the jump-host Ssh object, and the second and third are the destination SSH hostname and port.

Background: This chains the tunnel through a "jump host" (bastion): the application reaches a gateway server, then tunnels onward to an SSH server that is only accessible from inside the network. Each hop authenticates separately with its own credentials. The result is a normal SshTunnel — still requiring its own authentication and BeginAccepting — whose transport is routed through the first connection.

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Tcl


load ./chilkat.dll

set success 0

#  Demonstrates the SshTunnel.ConnectThroughSsh method, which connects to an SSH server through
#  an already connected and authenticated Ssh object (a jump host).  The 1st argument is the Ssh
#  object, and the 2nd and 3rd are the destination SSH hostname and port.

set sshJump [new_CkSsh]

#  Connect and authenticate to the jump host first.
set sshPort 22
set success [CkSsh_Connect $sshJump "jump.example.com" $sshPort]
if {$success == 0} then {
    puts [CkSsh_lastErrorText $sshJump]
    delete_CkSsh $sshJump
    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.
set password "mySshPassword"

set success [CkSsh_AuthenticatePw $sshJump "myJumpLogin" $password]
if {$success == 0} then {
    puts [CkSsh_lastErrorText $sshJump]
    delete_CkSsh $sshJump
    exit
}

#  Set up the tunnel and connect to the target SSH server through the jump host.
set tunnel [new_CkSshTunnel]

CkSshTunnel_put_DestHostname $tunnel "db.internal.example.com"
CkSshTunnel_put_DestPort $tunnel 5432

set success [CkSshTunnel_ConnectThroughSsh $tunnel $sshJump "ssh.internal.example.com" $sshPort]
if {$success == 0} then {
    puts [CkSshTunnel_lastErrorText $tunnel]
    delete_CkSsh $sshJump
    delete_CkSshTunnel $tunnel
    exit
}

#  Authenticate to the target SSH server (its own credentials).
set success [CkSshTunnel_AuthenticatePw $tunnel "mySshLogin" $password]
if {$success == 0} then {
    puts [CkSshTunnel_lastErrorText $tunnel]
    delete_CkSsh $sshJump
    delete_CkSshTunnel $tunnel
    exit
}

#  After authenticating, call BeginAccepting to start listening for local connections to forward.

set waitForThreadExit 1
set success [CkSshTunnel_CloseTunnel $tunnel $waitForThreadExit]
if {$success == 0} then {
    puts [CkSshTunnel_lastErrorText $tunnel]
    delete_CkSsh $sshJump
    delete_CkSshTunnel $tunnel
    exit
}

CkSsh_Disconnect $sshJump

delete_CkSsh $sshJump
delete_CkSshTunnel $tunnel