Network Fundamentals

What this domain actually tests

The groundwork: network components, topology architectures (two-tier, three-tier, spine-leaf), cabling and interfaces, and addressing.

And addressing means subnetting, which deserves to be treated as its own project.

The traps

You must subnet while thinking about something else

This is what separates CCNA subnetting from Network+ subnetting. The CCNA does not usually ask you a clean subnetting question. It asks you to trace a packet through a topology, or to work out why host A cannot reach host B — and subnetting is a sub-step you must perform while doing something harder.

That only works when the calculation is automatic. By week three you should be under 30 seconds for standard problems, and you get there by doing ten a day from week one.

Use the block-size method and stop converting to binary — you do not have the seconds. For a /27, the mask ends in .224, so the block is 256 − 224 = 32. Subnets land on .0, .32, .64, .96, and each broadcast is one below the next network.

Worked example: 192.168.1.100/26. Block size 64 → blocks 0–63, 64–127, 128–191, 192–255. Network .64, broadcast .127, usable .65–.126.

Now: is 192.168.1.200/26 on the same subnet? Block 192–255 — no. Different subnet, needs a router. That is the real exam question, wearing a troubleshooting costume.

IPv6 is not optional

Abbreviation rules (drop leading zeros; :: replaces one run of consecutive zero groups, and only one). Address types: global unicast (2000::/3), link-local (fe80::/10 — always present, used for neighbour discovery and OSPFv3 adjacencies), and unique local. Plus EUI-64, where the MAC is expanded into an interface ID with fffe inserted in the middle and the 7th bit flipped.

Candidates skimp on IPv6 because it feels secondary. It is not.

Topologies

Two-tier (collapsed core: access + distribution), three-tier (access, distribution, core), and spine-leaf (every leaf connects to every spine — used in datacentres for predictable east-west latency).

How to study it

Ten subnetting problems a day, every day, from week one. Not a subnetting week — a subnetting habit. This is the single highest-return habit available to a CCNA candidate.

Then give IPv6 its own dedicated sessions rather than tacking it on. Abbreviate twenty addresses by hand.

At 20% this domain is a fifth of the exam by weight — but its real weight is higher than that, because subnetting is load-bearing for the routing and troubleshooting questions in every other domain.