IP Addressing Basics
How does a network know which computer to deliver a packet to?
- Describe the structure of an IPv4 address
- Distinguish public and private addresses
- List the three private address ranges
Overview
Every device on an IP network has an address — like a house number. The IP address is what lets a switch, router or web server pick the right destination out of billions.
IPv4 structure
An IPv4 address is 32 bits, written as four decimal numbers 0–255 separated by dots — for example 192.168.1.15. It has a network part (identifies the network) and a host part (identifies the device within it). A subnet mask tells us where one ends and the other begins.
Public vs private
Public addresses are routable on the Internet and must be unique globally. Private addresses are for internal LANs only and can be reused anywhere. Three ranges are private: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16.
IPv6 note
IPv4 has only about 4.3 billion addresses — not enough for the modern world. IPv6 (128-bit) fixes this but rolls out slowly. For now most home networks still use IPv4 with private ranges and a router that translates to a single public address (NAT).
Classify Addresses
- For each address, label public or private: 192.168.1.1, 8.8.8.8, 10.20.30.40, 172.20.5.5, 74.125.24.100.
- State the private range for each private address.
- How many bits in an IPv4 address?
Reveal answer
32.
- Name the three private IPv4 ranges.
Reveal answer
10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16.
- What does NAT do?
Reveal answer
Translates many private IPs to a single public IP so they can share Internet access.
Run 'ipconfig' on a school PC. Is its IP public or private? Then visit whatismyip.com — is that address the same?