If you want to run a BBS, you’ll almost certainly need to read on. The most interesting, and useful, types of DNS records are A records, MX records, and CNAME records. An A record usually matches a single name to a single number.
For instance, as I write this, it matches the domain name “technopagan.org” to the number “24.2″.
If a domain doesn’t have an MX listed, the address from the A record will be used. It specifies aliases – other names that a computer answers to.
If you want to run a BBS, or Web server, or any number of other services, on your home computer, though, having your IP address change all the time is a real problem.
Enter DDNS, otherwise known as Dynamic DNS services or Free DNS.
(about 4.29e9, 4 billion or so) possible numeric addresses for the Internet in IPv4.
In practice, though, many of them were allocated in an inefficient manner a long time ago, in a way that can’t easily be undone today.