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← CourseIP Addressing~4 min read

IP addresses: every device needs a unique one

What an IP address is

An IPv4 address is four numbers 0–255 separated by dots, like 192.168.1.10. It identifies one network interface. On a local network every device must have a different IP - two devices with the same address collide, and traffic for that address becomes unreliable.

Private vs public

Some ranges are reserved for private networks (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16). They're reused in every home and office and are not routable on the public internet - which is why NAT exists to translate them on the way out.

The subnet mask decides who is 'local'

An address is paired with a mask (written as /24, /25, …). The mask splits the address into a network part and a host part. Two devices can talk directly only if they share the same network part - otherwise the traffic has to go through a router.

Concept cards

IPv4 address

A 32-bit address written as four 0–255 octets (e.g. 192.168.1.10).

A street address for one device on the network.

Private address

RFC1918 ranges (10/8, 172.16/12, 192.168/16) used inside private networks.

Apartment numbers - meaningful inside the building, not to the postal service.

Duplicate IP

Two devices assigned the same address, causing conflicts.

Two houses with the same address - the mail gets confused.

Now try it
M2-03Duplicate IP
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