What is the name of the string that a service returns when you establish a tcp connection via telnet?

cat pants

5/4/24, 12:33 AM

If you telnet to an ssh server, it will establish a connection and return a string, something like SSH-2.0-OpenSSH.... etc.

Something similar happens if you connect to a mysql server.

What exactly is the name of the string that the service returns? It's not a "header", since we aren't talking about http(s) here.

Similarly, it's also possible to send commands via telnet, for example, you can connect to an email server and send an email this way if you wanted to. What is the name of the commands one would send? They aren't exactly "POST" requests, again, since we aren't using http(s) here.

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telnet

tcp

joeqwerty

5/4/24, 1:01 AM

Logon banner, greeting, message of the day, etc.

joeqwerty

5/4/24, 1:03 AM

The commands you use with SMTP are called... wait for it... SMTP commands. - https://www.samlogic.net/articles/smtp-commands-reference.htm

Score:1

Server

davey

5/4/24, 5:36 AM

What exactly is the name of the string that the service returns? It's not a "header", since we aren't talking about http(s) here.

This rfc4253 refers to it as the "identification string" in section 4.2 Protocol Version Exchange.

Similarly, it's also possible to send commands via telnet, for example, you can connect to an email server and send an email this way if you wanted to. What is the name of the commands one would send? They aren't exactly "POST" requests, again, since we aren't using http(s) here.

The rfc4253 goes on to explain how to setup the rest of the connection. I've not seen an example of sending commands to an SSH server. At the point the TCP connection is made with the telnet client and the banner received the client would need to agree on things like encryption algorithms, compression and so on.

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EN: What is the name of the string that a service returns when you establish a tcp connection via telnet?

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