Visual Basic 6.0

SSH Tunnel TCP Socket Options

Demonstrates tuning the underlying TCP socket with the SoRcvBuf, SoSndBuf, TcpNoDelay, OutboundBindIpAddress, and OutboundBindPort properties. These normally should be left at their defaults.

Background: These are low-level knobs for specific situations. Larger send/receive buffers can improve throughput on high-bandwidth, high-latency ("long fat") links; TcpNoDelay disables Nagle's algorithm to cut latency for small interactive packets at the cost of efficiency; and binding the outbound socket to a specific local address or port is occasionally required by firewall rules or multi-homed hosts. Change them only with a concrete reason, since the defaults are tuned for the common case.

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Visual Basic 6.0

Dim success As Long
success = 0

'  Demonstrates tuning the underlying TCP socket with the SshTunnel properties SoRcvBuf, SoSndBuf,
'  TcpNoDelay, OutboundBindIpAddress, and OutboundBindPort.
'  
'  These normally should be left at their defaults; adjust them only for specific performance or
'  networking requirements.

Dim tunnel As New ChilkatSshTunnel

'  Socket send/receive buffer sizes, in bytes.  Larger buffers can help throughput on
'  high-latency links.
tunnel.SoRcvBuf = 4194304
tunnel.SoSndBuf = 262144

'  Disable Nagle's algorithm to reduce latency for small, interactive packets.
tunnel.TcpNoDelay = 1

'  Bind the outbound socket to a specific local address/port before connecting.  0 (the default)
'  lets the OS choose the local port; an empty address lets the OS choose the interface.
tunnel.OutboundBindIpAddress = "192.168.1.50"
tunnel.OutboundBindPort = 0

tunnel.DestHostname = "db.internal.example.com"
tunnel.DestPort = 5432

Dim sshPort As Long
sshPort = 22
success = tunnel.Connect("ssh.example.com",sshPort)
If (success = 0) Then
    Debug.Print tunnel.LastErrorText
    Exit Sub
End If

'  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.
Dim password As String
password = "mySshPassword"

success = tunnel.AuthenticatePw("mySshLogin",password)
If (success = 0) Then
    Debug.Print tunnel.LastErrorText
    Exit Sub
End If

Dim listenPort As Long
listenPort = 1080
success = tunnel.BeginAccepting(listenPort)
If (success = 0) Then
    Debug.Print tunnel.LastErrorText
    Exit Sub
End If

Debug.Print "Tunnel established with custom socket options."

Dim waitForThreadExit As Long
waitForThreadExit = 1
success = tunnel.CloseTunnel(waitForThreadExit)
If (success = 0) Then
    Debug.Print tunnel.LastErrorText
    Exit Sub
End If