Stage 1 of 10 · 8 lessons · ~5 weeks

How networks work and subnetting

Learn the layered models, TCP and UDP, the ports you will see every day, and IPv4 and IPv6 addressing, then practise subnetting until it is automatic.

Start: The OSI and TCP/IP models

Lessons· one lesson for each topic, in this order

Do this

Draw the OSI and TCP/IP models from memory with one protocol and one device per layer.
Learn the 20 most common port numbers and their transport protocol.
Do ten subnetting questions a day for two weeks without a calculator.
Write a VLSM plan for a small office with four departments and two router links.
Shorten and expand five IPv6 addresses and name their types.
Capture a DHCP exchange and a DNS lookup in Wireshark and label each packet.

Start with· follow one of these

PlatformFree
Cisco Networking Academy
Cisco · Beginner
Start with the free, self-paced Networking Basics course; it uses Packet Tracer from the first modules
VideoFree
Computer Networking: A Top-Down Approach (Video Lectures)
Jim Kurose and Keith Ross · Intermediate
Free university-level lectures from the authors of the classic textbook, for the why behind every layer

Practise

Cisco Packet Tracer
Build a two-subnet network and use simulation mode to watch ARP, DHCP and pings step by step

Keep handy

Wireshark User's Guide
Capture your own traffic and read real headers; the display filter chapter is the one to bookmark

Also worth your time

TCP vs UDP: The Key Differences Every Developer Should Know (opens in a new tab)Read
A clear comparison of the two transport protocols and when each one fits
Beej's Guide to Network ProgrammingGo deeper
If you code, write a tiny TCP and UDP client and server to see the transport layer from the inside

Before moving on: You can subnet any /20 to /30 in under a minute without a calculator, write a VLSM plan for a small office, and explain step by step, with ARP, MACs and IPs, how a ping crosses a router.

Tauseef's advice

Subnetting is the one skill you cannot skip or look up in the exam, and it is used in every later stage. Do ten questions every day for two weeks, on paper. Sefism also has a separate Networking basics cheat sheet for the wider picture (HTTP, DNS, how the internet works); this roadmap goes deeper into the engineering side.