In IPv4 addressing, what is the valid first-octet range that identifies a Class C network address block?

Introduction: Classical IPv4 “classful” addressing divides the address space into Classes A, B, C, D, and E based on the value of the first octet. Although classless routing (CIDR) is dominant today, understanding classful ranges remains a common exam topic.

Given Data / Assumptions:

• IPv4 uses four octets, each 0–255.
• Class C networks historically used smaller subnets with many networks and few hosts.
• We are asked only for the first-octet range that denotes Class C.

Concept / Approach: In classful IPv4: Class A = 1–126, Class B = 128–191, Class C = 192–223, Class D (multicast) = 224–239, Class E (experimental) = 240–255. Loopback uses 127.x.x.x and is not part of these usable network ranges.

Step-by-Step Solution:

Verification / Alternative check: Binary prefix: Class C addresses begin with 110 in binary for the first octet, i.e., decimal 192–223.

Why Other Options Are Wrong:

• 192–255: includes multicast (224–239) and experimental (240–255) ranges.
• 192–226: arbitrarily truncates the valid upper bound (should be 223).
• 128–191: this is Class B.
• 1–126: this is Class A (excluding 127 loopback).

Common Pitfalls: Mixing classful ranges with CIDR masks; assuming 127 is Class A usable space (it is reserved for loopback).

Final Answer: 192–223.