Why does the HTTP GET command on page 654, GET https://www.cs.princeton.edu/index.html HTTP/1.1 contain the name of the server being contacted? Wouldn't the server already know its name? Use Telnet, as in Exercise 14, to connect to port 80 of an HTTP server and find out what happens if you leave the host name out.
Exercise 14
Most Telnet clients can be used to connect to port 25, the SMTP port, instead of to the Telnet port. Using such a tool, connect to an SMTP server and send yourself (or someone else, with permission) some forged email. Then examine the headers for evidence the message isn't genuine.