Stop 02 · Networking Fundamentals for CloudTopics · 2/9

IP Addressing & Subnetting

In short

Every device on a network needs an address, and subnetting splits big networks into smaller neighbourhoods. You'll use this daily to read logs, write firewall rules and design cloud networks.

How devices are uniquely identified on a network, and how subnetting divides a larger network into smaller, manageable segments — essential for designing a cloud VPC's address space correctly from day one.

The blob drops a letter into one wing's mailbox at a three-wing apartment complex.

Think of it like this

An apartment complex with wings

The society's address gets mail to the gate. Wing A, B or C narrows it down, and the flat number finds the exact door. An IP address works the same: the network part is the society and wing, the host part is the flat.

Watch it happen

Reading 192.168.10.37/24

192

168

1/5An IPv4 address is four numbers from 0 to 255, called octets. Each octet is 8 bits, so 32 bits total.

The big ideas

What you need to know

CIDR notation

The /number says how many bits are the network. Bigger number, smaller subnet. /24 has 256 addresses, /28 has 16.

Private ranges

10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 are for internal use. NAT translates them to a public IP.

Subnets as security zones

Putting servers, staff laptops and guests in different subnets lets firewalls control traffic between them.

IPv6 is coming

IPv6 uses 128-bit addresses written in hex, like 2001:db8::1. Same ideas, far more addresses.

See it in code

Walk through the code

bash

1# Show your own IP address and prefix2ip addr show          # Linux3ipconfig              # Windows4ifconfig | grep inet  # macOS5 6# Python can do subnet maths for you7python3 -c "import ipaddress as i; n=i.ip_network('10.0.5.0/26'); print(n.num_addresses, n[1], n[-2])"

1/2Each OS shows your address with a prefix or netmask. 255.255.255.0 is the same as /24.

A /26 has 64 addresses. The first is the network address and the last is broadcast, so usable hosts run from .1 to .62.

Save yourself the pain

Common mistakes

Oops

Thinking a /24 gives you 256 usable hosts.

Do this instead

Two addresses are reserved: the network address and the broadcast address. That leaves 254.

Oops

Writing firewall rules for single IPs when a range is meant.

Do this instead

Use CIDR blocks like 10.0.5.0/26 for a whole subnet. It's shorter and fewer rules get forgotten.

Your mission

Subnet your hostel

~25 min

Quick check

Which address is in the same subnet as 172.16.4.10/24?

Go deeper

1Practice calculating a subnet's usable IP range given a CIDR notation (e.g. /24).
2Learn the difference between public and private IP address ranges.
3Use a subnet calculator to check your manual calculations until it's second nature.