Subnetting Practice: Find the First Usable Host on the 3rd Subnet (172.16.0.0/21)

In this video, we walk step-by-step through a real-world subnetting question:
You are given the network 172.16.0.0/21 and need to assign your router the first usable host address on the third subnet.

You’ll learn how to:

Understand what a /21 subnet mask means

Calculate the block size for /21 networks

Identify subnet boundaries

Count subnets correctly (including subnet numbering)

Find the first usable IP address for a router

This type of question is very common on CompTIA Network+, CCNA, and IT support exams, and it’s also a skill you’ll use in real network design and configuration.

📌 Perfect for:

Network+ exam prep

CCNA subnetting practice

IT support and help desk students

Anyone struggling with subnet math

If subnetting has ever felt confusing, this explanation will make it clear and repeatable.

👍 Like the video, subscribe to Informatik Lab, and check out the full subnetting playlist for more practice problems.

Видео Subnetting Practice: Find the First Usable Host on the 3rd Subnet (172.16.0.0/21) канала Informatik Lab