Stage 1 · Lesson 3 of 8
IPv4 addresses, masks and prefixes
An is 32 bits, written as four numbers from 0 to 255, such as 192.168.10.25. The prefix length, written /24 or as the mask 255.255.255.0, says how many of the leading bits name the network; the remaining bits name a host on it.
The first address in a range is the network address and the last is the address, so neither can be given to a device. Private ranges (10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16) are used inside organisations and translated to public addresses at the edge.
Being able to look at 10.1.4.0/22 and say which addresses it covers is the single most used skill in this job.
Common trapworking in decimal and guessing: convert the interesting octet to binary until the pattern is obvious.
A question to check yourself, an AI practice session and 1 cheat sheet entry come with the full roadmap. Unlock
Resources for this stage
Start with· follow one of these
- PlatformFreeCisco Networking Academy
Cisco · Beginner
Start with the free, self-paced Networking Basics course; it uses Packet Tracer from the first modules
- VideoFreeComputer 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
Keep handy
Also worth your time
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