How the Internet works, part 1

Hostnames and DNS

• What happens when you register a hostname
• Making a DNS query: host and dig
• Things other than A records: aliases and mail

Internet addresses

• What are IP addresses?
• Why have we run out of IPv4 addresses?
• IPv6 and its sloooowww adoption
• localhost and private IP addresses

Network communication

• Computers run programs, which listen at ports
• Port: a number that tells the computer which program to send the message to
• Restricted ports: 0-1023
• Registered ports: everything in /etc/services
• Once you learn enough Python, you too can write a program that listens at a port!

Network protocols

• This is how computer programs talk to each other
• Much like shells, programs have their own language that they expect

• Example! Talking to a mail server

    HELO digitalbyzantinist.org
    MAIL FROM:<mickey@digitalbyzantinist.org>
    RCPT TO:<aurum@well.com>
    DATA
    From: "Mickey Mouse" <mickey@digitalbyzantinist.org>
    To: Tara <aurum@well.com>
    Date: Wed, 12 Jul 2017 20:42:01 -0500
    Subject: my message
  
    Hello Tara! It's your old friend Mickey. Squeak.
    .
    QUIT
  

• Why might mail get caught in a spam filter?