Cambridge IGCSE Computer Science (0478) · lesson 13 of 35 · 25 min
IP Addresses
Every device on the Internet has an IP address — a unique numerical label used to identify and locate it. There are two versions:
IP addresses can be static (permanently assigned) or dynamic (assigned by a DHCP server each time a device connects).
DNS — Domain Name System
Humans remember names like www.bbc.co.uk; computers use IP addresses. DNS is a distributed database that translates domain names into IP addresses.
- You type www.example.com in your browser.
- Your device checks its local DNS cache.
- If not cached, it queries a recursive resolver (usually your ISP).
- The resolver queries root servers → TLD servers (.com) → authoritative server.
- The IP address is returned and cached for future use.
Packets and Packet Switching
Data sent over the Internet is broken into small chunks called packets. Each packet contains:
- Header: source IP, destination IP, packet number, TTL.
- Payload: the actual data (fragment of the message).
- Trailer: error-checking data (checksum).
Packets may take different routes through the network and arrive out of order. The receiving device reassembles them in the correct order using the packet numbers.
What does DNS do?
- Assigns IP addresses dynamically
- Translates domain names to IP addresses
- Encrypts web traffic
- Routes packets between networks
Answer: Translates domain names to IP addresses
DNS = Domain Name System; maps human-readable names to IP addresses.
How many bits are in an IPv4 address?
- 16
- 32
- 64
- 128
Answer: 32
IPv4 uses 32-bit addresses.
Why are messages broken into packets?
- To encrypt them
- To allow efficient routing and reassembly
- To reduce file size
- To assign IP addresses
Answer: To allow efficient routing and reassembly
Packet switching allows efficient use of network links and rerouting around failures.
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