How can I open a telnet connection and run a few commands?

C# 2.0 and Telnet - Not As Painful As It Sounds
http://geekswithblogs.net/bigpapa/archive/2007/10/08/C-2.0-and-Telnet---Not-As-Painful-As-It.aspx

Or this alternative link.

If you're going to use the System.Net.Sockets class, here's what you do:

• Create an IPEndpoint, which points to the specified server and port. You can query DNS.GetHostEntry to change a computer name to an IPHostEntry object.
• Create a socket object with the following parameters: AddressFamily.InterNetwork (IP version 4), SocketType.Stream (rides on InterNetwork and Tcp parameters), ProtocolType.Tcp (reliable, two-way connection)
• Open the socket like this: socket.Connect(endpoint); //yup, it's that simple Send your data using socket.Send(... wait, I forgot something. You have to encode the data first so it can fly across them wires.
• Use Encoding.ASCII.GetBytes to convert the nice message you have for the server into bytes. Then use socket.Send to send those bytes on their way.
• Listen for a response (one byte at a time, or into a byte array) using socket.Receive Don't forget to clean up by calling socket.Close()

You can [also] use a System.Net.Sockets.TcpClient object instead of a socket object, which already has the socket parameters configured to use ProtocolType.Tcp. So let's walk through that option:

1. Create a new TcpClient object, which takes a server name and a port (no IPEndPoint necessary, nice).
2. Pull a NetworkStream out of the TcpClient by calling GetStream()<

For simple tasks (such as connecting to a specialized hardware device with telnet-like interface) connecting via socket and just sending and receiving text commands might be enough.

If you want to connect to real telnet server you might need to handle telnet escape sequences, face terminal emulation, handle interactive commands etc. Using some already tested code such as Minimalistic Telnet library from GitHub (free) or some commercial Telnet/Terminal Emulator library (such as our Rebex Telnet) might save you some time.

Following code (taken from this url) shows how to use it:

// create the client 
Telnet client = new Telnet("servername");

// start the Shell to send commands and read responses 
Shell shell = client.StartShell();

// set the prompt of the remote server's shell first 
shell.Prompt = "servername# ";

// read a welcome message 
string welcome = shell.ReadAll();

// display welcome message 
Console.WriteLine(welcome);

// send the 'df' command 
shell.SendCommand("df");

// read all response, effectively waiting for the command to end 
string response = shell.ReadAll();

// display the output 
Console.WriteLine("Disk usage info:");
Console.WriteLine(response);

// close the shell 
shell.Close();