Internet Address Detective

Names for people, numbers for computers.

Your mission

You type a name, but the Internet runs on numbers. Follow www.hkmu.edu.hk as DNS turns it into an IP address, take that address apart bit by bit, build your own, and find out why your laptop has two addresses at once. Then crack six cases with your detective's notebook.

Experiment

Build IPv4 addresses bit by bit, look up names with DNS, and send data from a private network out to the Internet.

Your IPv4 address

Octet1286432168421

Type a number in each octet, or tap the bits to switch them on and off.

Website address

The DNS server's phonebook (example entries)

Domain name	IP address

Detective experiments

Try each one. They tick themselves off.

0 of 6 experiments done

Understand

Here is what the detective work was showing you, in the words you need for the exam.

IP address: a street address for devices

An IP address (Internet Protocol address) identifies a device, or an interface, on a network. Like a street address for a house, it lets data be sent to the correct destination. Routers use IP addresses to find the best path.

An IPv4 address is 32 bits, written as four 8-bit numbers called octets, separated by dots. Each octet can be 0 to 255, because 8 bits give 2⁸ = 256 patterns, from 00000000 = 0 to 11111111 = 255.

Decimal	192	168	1	10
Binary	11000000	10101000	00000001	00001010
Bits	8	8	8	8

4 × 8 = 32 bits, so there are 2³² = 4,294,967,296 possible IPv4 addresses, about 4.3 billion. Not all of them are for public use: some ranges are reserved for private networks and other special purposes.

DNS: the Internet's phonebook

Humans prefer domain names; computers communicate using IP addresses. The DNS (Domain Name System) translates one into the other:

1You type www.hkmu.edu.hk.
2Your device asks a DNS server to look up the name.
3DNS returns the IP address, e.g. 202.181.160.6.
4Your browser connects to that IP address and loads the website.

The parts of a URL

A URL (Uniform Resource Locator) tells your browser where to find a resource on the Internet. Each part has its own job:

Protocolhttps://	How data is transferred between browser and server
Host / subdomainwww	Often indicates the web server; optional
Domain namehkmu.edu.hk	Uniquely identifies the organisation or website
Path/about/	A particular page or resource on the website

Your laptop lives in two worlds

	Private IP	Public IP
Example	192.168.1.5	203.0.113.25
Assigned by	Your router	Your Internet Service Provider (ISP)
Used for	Communication inside your local network	Sending and receiving data with websites and online services
Reachable from the Internet?	Not directly	Yes: it represents your network to the Internet
Ranges / notes	10.x.x.x, 172.16.x.x – 172.31.x.x, 192.168.x.x	Can change over time (dynamic IP)

Think of a house: the private IP is your room number, and the public IP is the house address that people outside can see.

Exam tip

Remember the numbers: IPv4 = 32 bits = 4 octets × 8 bits, each octet 0 to 255 (so 256 or more is invalid), giving 2³² ≈ 4.3 billion addresses. To convert an octet, use the bit values 128 64 32 16 8 4 2 1: 192 = 128 + 64 = 11000000. Say that DNS translates a domain name into an IP address, like a phonebook. Name the URL parts in order: protocol, host (subdomain), domain name, path. A private IP works inside the local network and is assigned by the router; a public IP is assigned by the ISP and represents your network on the Internet.

Try Unit 5 exam questions Next game: The Secret Message Lab All Unit 5 games