Section 1.7 – Given a Scenario, Use Appropriate IPv4 Network Addressing

Posted filed under CompTIA Network+, CompTIA Security+.

This section focuses on core IPv4 addressing concepts and how to apply them in various networking scenarios. It covers public vs. private addressing, subnetting, and address classes. This knowledge is essential for IP planning, routing, and troubleshooting.

Public vs. Private IP Addresses

Public IP Addresses

  • Globally routable on the internet and assigned by IANA or regional registries

  • Must be unique worldwide

  • Used by internet-facing servers, routers, and services

Private IP Addresses (RFC1918)

Reserved for use within private networks; not routable over the public internet.

  • Class A: 10.0.0.0 – 10.255.255.255

  • Class B: 172.16.0.0 – 172.31.255.255

  • Class C: 192.168.0.0 – 192.168.255.255

  • Used in LANs, home networks, and internal enterprise environments

APIPA (Automatic Private IP Addressing)

Fallback IP assignment when DHCP is unavailable.

  • Range: 169.254.0.1 – 169.254.255.254

  • Used temporarily for local communication (no routing)

Loopback / Localhost
Reserved IP range for internal testing on a device.

  • 127.0.0.1 is the standard loopback address

  • Traffic never leaves the local device

Subnetting

Subnetting breaks a larger network into smaller logical segments to improve routing efficiency, security, and broadcast domain control.

VLSM (Variable Length Subnet Mask)

  • Allows use of different subnet masks within the same IP class

  • Increases IP address efficiency

  • Supports hierarchical addressing schemes

CIDR (Classless Inter-Domain Routing)

  • Uses slash notation (e.g., /24) to define subnet masks regardless of traditional class boundaries

  • Example: 192.168.1.0/26 = 64 addresses

  • Promotes route summarization and flexible subnetting

IPv4 Address Classes

Originally, IPv4 addresses were divided into classes based on their first octet. While largely replaced by CIDR, these concepts still appear in legacy systems and exam questions.

Key Terms

  • IPv4

  • Public IP

  • Private IP

  • RFC1918

  • Loopback

  • APIPA

  • Subnetting

  • VLSM

  • CIDR

  • IP Classes

  • /24 Notation

  • Class A/B/C

  • Multicast

  • Reserved Range

Exam Tips 

  • Memorize the RFC1918 private IP ranges and their class designations

  • Know the APIPA range and when it appears (usually after a DHCP failure)

  • Understand the difference between CIDR and VLSM:

    • CIDR = representation format

    • VLSM = allows subnet size variation

  • Expect scenario-based questions where you’re asked to:

    • Choose a valid subnet

    • Identify broadcast ranges

  • Be prepared to classify given IP addresses into Class A, B, or C and explain their default subnet mask

FAQ

Q: Why are we running out of IPv4 addresses?
A: IPv4 has about 4.3 billion addresses, but the internet has more devices than that. IPv6 solves this problem.

Q: What happens if two private networks use the same subnet?
A: They cannot directly communicate. You’ll need NAT or readdressing.

Q: What’s the difference between /30 and /31 subnets?
A: /30 allows 2 usable hosts (common for point-to-point links). /31 is used in special cases (e.g., router links, no broadcast).

Are you looking to break into the exciting field of Networking? Join our 5-day CompTIA Network+ Bootcamp Training and build your networking knowledge and skills. 

Comments are closed.