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DEMO: Hosts

This lesson covers how to identify the host portion of IPv4 addresses using classful addressing rules, building on the foundational skill of isolating network bits.

⚑ Complete this video to capture a CTF flag worth 1 point.

About this video

Classful IPv4 addressing divides an address into a network portion and a host portion based on the value of the first octet. A first octet in the range associated with Class A means only that octet represents the network, leaving the remaining three octets as host bits. Class B and Class C addresses follow different boundaries, progressively reducing the number of available host bits as the network portion grows. Being able to quickly and accurately identify host bits is a foundational subnetting skill. Mistakes at this stage compound when working through subnet masks, CIDR notation, and address allocation, so accuracy here is essential before advancing. Repeated practice with varied address examples builds the pattern recognition needed to work through these problems reliably under real-world conditions.

What you'll learn

What's covered

Identifying Host Portions

Aligned to

CompTIA Network+
1.7 Given a scenario, use appropriate IPv4 network addressing.
Cisco CCNA
1.6 Configure and verify IPv4 addressing and subnetting.
Cisco CCST Networking
2.2 Identify IPv4 addresses and subnet formats.
CompTIA A+ Core 1
2.6 Compare and contrast common network configuration concepts.

Key terms

IP Address
A numerical label assigned to each device connected to a network that uses the Internet Protocol.
Subnet Mask
A 32-bit number that divides an IP address into network and host portions.
Classful Addressing
An early IPv4 addressing scheme that divided the address space into fixed classes (A, B, and C for hosts; D for multicast; E reserved) based on the leading bits of the address, with each class defining a fixed boundary between the network and host portions. Classful addressing was replaced by CIDR because it wasted large blocks of address space.
Network Layer
Layer 3 of the OSI model, responsible for logical addressing and routing data packets between networks.
Octet
One of the four 8-bit sections of an IPv4 address, each separated by a dot in dotted decimal notation and representing a decimal value from 0 to 255. For example, in 192.168.1.1, the four octets are 192, 168, 1, and 1.

Transcript

In our last video we identified the network portion of the address, and this time we're going to identify the host portion of the addresses. So we're going to do something similar with this, but it's going to be the host side.

The first thing I'm going to look at is this first octet. This is 102. That is a class A; it pulls in the class A range. So that first octet is the network portion of it, that makes the rest of it the host bits. So I'm going to circle the host bits in this case.

Go through and do the rest of these, and then you can see how accurate and how close you came. And here are the answers. Check your work and make sure you did it all correctly. If not, once again, this is pretty critical before you move forward, so make sure you have this down.

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