How to perform "double hop" via SFTP/SSH in .NET?

Question

In my scenario i am trying to go from Local App Server -> Middle Server (DMZ) -> Client Server

I need to move files from the Local App Server to the Client Server and back.

So my question is what is the most widely used standard for doing this?

I am currently using WinSCP to connect to the Middle Server via SFTP, and then invoking a command on the Middle Server to download and upload files to the Client Server. I'm not really a fan of this, as i feel like its prone to error as i am manually entering a command, rather than using the WinSCP's library to upload and download. It also leaves me stuck when i try to list all files on the Client Server with a command, as the function returns void

I have looked at SSH.NET which seems like its more widely used, however i cant see any real way of performing a "double hop" with that library either.

Answer 1

With WinSCP .NET assembly, it's easy:

SessionOptions sessionOptions = new SessionOptions
{
    Protocol = Protocol.Sftp,
    HostName = "example.com",
    UserName = "username",
    Password = "password",
    SshHostKeyFingerprint = "ssh-rsa 2048 xxxxxxxxxxx...=",
};

sessionOptions.AddRawSettings("Tunnel", "on");
sessionOptions.AddRawSettings("TunnelHostName", "tunnel.example.com");
sessionOptions.AddRawSettings("TunnelUserName", "username");
sessionOptions.AddRawSettings("TunnelPasswordPlain", "password");
sessionOptions.AddRawSettings("TunnelHostKey", "ssh-rsa 2048 xxxxxxxxxxx...=");

using (Session session = new Session())
{
    session.Open(sessionOptions);

    // Your code
}

WinSCP GUI can generate a code template to connect through tunnel, like the one above, for you (except for the TunnelHostKey).

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With SSH.NET you can implement a port forwarding explicitly by:

• opening connection to the "Middle Server";
• creating a forwarded port;
• opening a second connection to the forwarded port.

For some example, see Connection to MySQL from .NET using SSH.NET Library.

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Another hackish solution is to execute ssh on the "Middle Server" to facilitate the second "hop".