Telnet is a wonderful tool for sysadmins and network application programmers. If you ever find yourself wearing either of these hats, you’ve got to know how to use telnet. Though, sometimes telnet requires a little too much from the user in order to get anything done. Netcat to the rescue! This is a tool that I’ve seen used before, but only recently really looked in to. Netcat (’nc’) can be used as a server or a client, Netcat can be used to transmit files, Netcat can even be used as a port-scanner. Once I found myself trying to debug a web server with telnet. It was a pain to type in all the HTTP request headers by hand. If I would have known about Netcat, I could have just done this each time:
nc host 80 < request.txt
and just edited the request.txt file each time I wanted to try something different. Go read the man page (man nc), it’s actually well-written.
Now for the next cool tool! Ever wanted to do some testing on a server that uses TLS/SSL? Telnet obviously isn’t the answer. OpenSSL to the rescue! s_client lets you have the simple power of telnet, but it takes care of all the overhead of TLS/SSL. You can use s_client to test a server to find out if it will allow SSL2 sessions, or find out what happens if the client only requests certain ciphers. s_server gives you similar control from the server side.