IP Addressing & Protocols: an interactive course
IP Addressing & Protocols is an interactive IP addressing course about how devices find each other on a network. Its 25 short sections cover IPv4 addresses as four octets of bits, network and host parts, subnet masks and CIDR prefixes, network and broadcast addresses, counting hosts, ports, TCP and UDP, private addresses and NAT, DHCP, DNS and IPv6.
More than half the sections are practice, with random addresses each time, so subnetting goes from confusing to routine.
What the course covers
| Sections | Topic | What you do |
|---|---|---|
| 1 to 3 | What an IP address is: four numbers, 32 bits | Read the value of an octet from its bits |
| 4 to 5 | Network part and host part | Decide whether two addresses are on the same network |
| 6 to 9 | Subnet masks, CIDR prefixes and network addresses | Turn masks into prefixes, then find the network address |
| 10 to 12 | Broadcast addresses, host ranges and host counts | Sort addresses into network, host or broadcast, then count hosts |
| 13 to 16 | Ports, TCP and UDP | Match well-known ports to services, then choose TCP or UDP |
| 17 to 19 | Private addresses and NAT | Spot private addresses, then route a reply through NAT |
| 20 to 23 | DHCP and DNS | Fill in the DHCP messages, then order a DNS lookup |
| 24 to 25 | IPv6 | Shorten an IPv6 address |
Addresses and subnets
An IPv4 address such as 192.168.1.20 is four octets, each 8 bits, so each number runs from 0 to 255. A subnet mask, or a CIDR prefix such as /24, says how many bits are the network part; the rest identify the host. From the mask you can find the network address, the broadcast address and how many devices fit. Our guides to IP addresses and subnet masks go deeper on both.
Ports and transport
An IP address gets data to a device; a port number gets it to the right program, such as 443 for secure web pages. TCP opens a connection with a three-way handshake and resends anything lost, while UDP skips both for speed. See what is TCP for more.
Everyday services
Private addresses only work inside a home or office, and NAT lets them share one public address. DHCP hands each new device an address automatically, DNS turns names into addresses, and IPv6 uses 128-bit addresses because IPv4 has run short.
Try a question from the course
Each octet is 8 bits, and the leftmost bit is worth 128, halving each step to the right. The octet 11000000 has 1s under 128 and 64, so its value is 192. The octet 10101000 has 1s under 128, 32 and 8, which add up to 168.
Now read a new octet, then press Mark to check your answer in the course.
Turn one octet of an address from binary to decimal, or decimal to 8 bits.
Press Mark to have your answer marked in the IP Addressing & Protocols course.
Who this course is for
- A-level and university computing students learning subnetting, TCP and UDP and network services.
- GCSE students who want to go beyond the basics of IP addresses and protocols.
- Beginners in IT and networking who need subnetting to become second nature.
What you need to know first
The course page lists Binary, Hexadecimal & Decimal and Networking Hardware first. Binary is essential: subnetting is mostly reading and comparing bits.
How long it takes
There are 25 sections and most take a few minutes. Learners without a plan can open two sections of a course a day, in order, so the whole course takes 13 days. A plan removes the daily limit and lets you go straight to any topic, such as counting hosts.
Common questions
Is this IP addressing course free?
What is a subnet mask?
How many hosts are in a /24 network?
What is the difference between TCP and UDP?
What do DHCP and DNS do?
Why do we need IPv6?
Revision cards
Say the answer first, then flip the card to check it.
Where to go next
- Solve it
Number Base Converter
Convert between binary, hex and decimal and add in binary
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IP Addressing & Protocols
IPv4, IPv6, subnetting and the protocols that power the internet
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GCSE Computer Science
A new exam-style paper every day, with instant marking and a mark scheme
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Computer Science · NetworksWhat is an IP address? IPv4, IPv6 and how to find yoursWhat an IP address is and how it works: IPv4 and IPv6, public vs private, static vs dynamic, what your IP reveals and how to find yours.