Which of the following are classful addresses? (Select all that apply below)

Classful addressing is an IP addressing architecture that divides the address space into five classes (A, B, C, D, E), where the class is determined by the first octet. Each class has a predefined, default subnet mask.

Class A: First octet 1-126, default mask /8.

Class B: First octet 128-191, default mask /16.

Class C: First octet 192-223, default mask /24.

Option A (10.225.30.0/8) is a Class A address with its correct default /8 mask. Option C (172.16.0.0/16) is a Class B address with its correct default /16 mask. Therefore, both are classful addresses.

B. This is a Class A address (10.x.x.x) but uses a /16 mask instead of the default /8. This is a classless (CIDR) address.

D. This is a Class B address (172.16.x.x) but uses a /24 mask instead of the default /16. This is a classless (CIDR) address.

1. Fortinet Training Institute. (2022). FortiGate Infrastructure 7.2 Study Guide. Fortinet

Inc. Page 11

"IP Addresses and Subnet Masks" section describes the default prefixes for each address class: "Class A networks use a /8 prefix... Class B networks use a /16 prefix... Class C networks use a /24 prefix."

2. Postel

J. (1981). RFC 791: Internet Protocol. Information Sciences Institute

University of Southern California. Section 3.2

"Addressing

" specifies the bit allocation for network and host portions for each class

which defines the default masks (e.g.

Class A has 8 bits for network

Class B has 16 bits for network).

3. Comer

D. E. (2006). Internetworking with TCP/IP

Volume 1: Principles

Protocols

and Architecture (5th ed.). Pearson Prentice Hall. Chapter 3

"Classful Internet Addresses

" pages 41-43

provides a detailed explanation of the address classes and their corresponding default network masks.