An address for every house: the IP

Every house has an address

Last time we learned about packets.
A packet was a piece plus an address tag.
But whose address is that tag?
It is the address of the receiving computer.
Think about sending a letter.
You write the recipient's house address,
and the mail carrier finds that house.
On the internet too, every computer
must have an address of its own.

Tap a house to attach an address sign. One computer, one address.

The more addresses you attached,
the clearer which house was which.
Houses without addresses
were just identical boxes.
Once an address appears,
you can finally point and say "there."
But that address,
what does it actually look like?
Let's take a look next.

An address made of numbers

People's addresses use words,
but a computer's address uses numbers.
Computers are good with numbers.
An IP address is four slots
of numbers split by dots.
For example, 203.0.113.5.
Each slot is a number from 0 to 255.
The dots are fences between the slots.
Numbers, not words: that is the key.

Tap the address to inspect each slot. Four slots of numbers split by dots.

We looked at the four slots in order.
Each slot holds a number,
and dots divided the slots.
Written this way,
both people and computers can read it.
Different addresses have different slot numbers.
One bundle of these numbers
points to one computer in the world.
Now shall we go find it by that address?

Find it by the address

A packet has the destination address written on it.
The internet reads that address
and sends the packet to the right computer.
Just as the mail carrier reads the address on the envelope
and drops the letter into that house.
As long as the address is correct,
among countless houses
it finds exactly that one.
The address is the guide.

Read the packet's destination address, then tap the house with that address to deliver.

Tap the house matching the destination,
and the packet arrives exactly.
Tap a different house
and the address does not match, so no delivery.
This is how the internet works.
Read the address, find the matching one,
and send it there.
But there is one condition.
The address must be the only one of its kind.

An address must be unique

If two houses in a town share one address,
what happens?
The mail carrier gets confused about
which house to drop the letter in.
IP addresses are the same.
If two computers have the same address,
the packet gets confused about where to go.
So an address
must be the only one in the world.
Only then does it arrive exactly, without confusion.

Send to the houses with a clashing address and to those with a unique address. Clashing confuses, unique arrives exactly.

Sent to the houses with a clashing address,
the packet got confused between the two.
Sent to a unique address,
it arrived straight at one house.
The only difference
was whether the address was one of a kind.
That is why, on the real internet,
addresses are handed out carefully
so that no two ever clash.

Let's wrap up

Gathered on one line, it's this.
Every computer has a unique address.
That is the IP address.
It's written as four slots of numbers split by dots.
A packet reads the destination address
and finds the right computer.
The address must be one of a kind
so nothing gets confused.
Like a house address, one of a kind in the world.

Tap the key points in order to review. (address for every house → number address → find by address → must be unique)

Now you know every computer has an address.
But numbers like 203.0.113.5
are a bit hard for people to remember, right?
What we usually use are names made of words.
There is a clever help desk
that turns those names into number addresses.
Next lesson, let's meet together
that help desk that turns names into addresses.