Which IPv4 address range is the Class B private address space defined for internal use?

Introduction / Context:
Along with the Class A and Class C style private ranges, IPv4 defines a Class B style private address block intended for internal network use. Knowing this range helps network administrators design addressing schemes and recognize non-routable internal addresses when troubleshooting.

Given Data / Assumptions:

• We focus on the Class B style private address block defined by RFC 1918.
• Several ranges are provided, including other private ranges and a generic class range.
• Only one option is the correct private Class B style range.
• We assume standard IPv4 and traditional terminology.

Concept / Approach:
RFC 1918 defines 172.16.0.0/12 as a private address space. A /12 mask covers 172.16.0.0 through 172.31.255.255. This range sits between the smaller 192.168.0.0/16 and the larger 10.0.0.0/8 private blocks and is often associated with Class B sized networks in older terminology.

Step-by-Step Solution:
1. Recall that the Class B style private range in RFC 1918 is 172.16.0.0/12.2. The /12 mask means the first twelve bits are fixed, which corresponds to addresses from 172.16.0.0 to 172.31.255.255.3. Compare this range against the options provided.4. Option A matches exactly 172.16.0.0 – 172.31.255.255.5. Therefore, option A is the correct Class B private address space.

Verification / Alternative check:
Network textbooks and RFC 1918 itself list this range explicitly. It is commonly used in medium to large organizations that want more addresses than are available in 192.168.0.0/16 but do not require the entire 10.0.0.0/8 block.

Why Other Options Are Wrong:
Option B, 10.0.0.0 – 10.255.255.255, is the Class A style private range. Option C, 192.168.0.0 – 192.168.255.255, is the Class C style private range. Option D, 128.0.0.0 – 191.255.255.255, represents the entire historical Class B public space, not the specific private subset defined by RFC 1918.

Common Pitfalls:
People sometimes assume that any 172.x.y.z address is private, but only the subset from 172.16.0.0 to 172.31.255.255 is defined as private. Addresses like 172.32.0.1 are public and routable. Memorizing the exact start and end of the private range avoids such mistakes.

Final Answer:
172.16.0.0 – 172.31.255.255