Addresses on a Network: Naming a Machine and Naming a Page
For one machine to send data to another it needs an address that is unique on the network. A web address is a different kind of name, one that has to be looked up and turned into a machine address before anything can be sent.
What a learner can do afterwards
- Say what an address has to promise for a message to arrive, and why two machines on one network cannot share one
- Break a web address into the part naming a machine and the part naming a page on it
- Describe why the name has to be looked up first, and what happens if the lookup fails
1 · Read
Every device on a network needs an address that is unique. Just as homes need mailing addresses to receive mail, computers need an IP address to receive messages. A message must carry the other computer's address, or the network has no idea where it should go.
An IPv4 address looks like 74.125.20.113: four numbers, each from 0 to 255. The first part names the network and the last part names the single machine on it, a bit like a phone number with a country code and an area code. Try typing such a number into a browser. It still arrives.
A web address is a different kind of name. It names a machine plus a page on it, in words humans like. Before anything can be sent, that name must be looked up and turned into the machine's number. If two machines shared one address, a message could land on either or get lost.
If the lookup fails, nothing is sent, because a name without a number points nowhere. So when a page will not load, the name never became an address. The machine part and the page part only work after the lookup succeeds.
Machines send to unique numbers, and web names must become numbers first.
2 · Watch
Take it off screen
Where it sits
Learn first
This opens up
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.