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CHAPTER 1. THE INTERNET

  Echo (port 7) an echo service, simply echos back what it receives

  Daytime (port 13) this returns the date and local time and ignores client

input

  FTP (ports 20,21) allows the client to transfer files of data to and from

the server.

  Telnet (port 23) allows the client to interact with the servers operating

system remotely

  SMTP (port 25) offers an email service for delivering email to a user on

the server

  DNS (port 53) domain name serving, returns IP addresses for domain

names

  WWW (port 80) uses the HTTP protocol and sends specified web pages

to the client.

  POP3 (port 110) offers another email service

Figure 1.1: Some of the most common services

USER

% telnet www.cs.brandeis.edu 13

Trying 129.64.2.3...

Connected to diamond.cs.brandeis.edu.

Escape character is '^]'.

Thu Aug 31 15:55:41 2000

Connection closed by foreign host.

Figure 1.2: Accessing the date service on port 13