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Difficulty: MediumPrivate IPv4 Addressing and RFC 1918

A network technician is configuring an isolated staging environment and must assign a dedicated IPv4 subnet using unroutable addresses specified in RFC 1918. Which of the following network prefixes represents a valid private IPv4 address block according to RFC 1918?

  1. 172.25.0.0/16Answer
  2. B
    172.33.0.0/16
  3. C
    192.169.1.0/24
  4. D
    11.0.0.0/8

Answer

172.25.0.0/16 is the valid RFC 1918 private IPv4 network prefix.
The prefix 172.25.0.0/16 lies within the 172.16.0.0/12 block reserved by RFC 1918 for private IPv4 networks (spanning from 172.16.0.0 to 172.31.255.255).

Step-by-Step Solution

1
Recall the defined RFC 1918 private IPv4 address ranges
Class A: 10.0.0.0/8 (10.0.0.0 – 10.255.255.255), Class B: 172.16.0.0/12 (172.16.0.0 – 172.31.255.255), Class C: 192.168.0.0/16 (192.168.0.0 – 192.168.255.255).
RFC 1918 explicitly reserves these three specific IP address blocks for private internal networks.
2
Evaluate the candidate prefixes against the RFC 1918 boundaries
The prefix 172.25.0.0/16 is inside the Class B range of 172.16.0.0 to 172.31.255.255. All other options fall outside the private boundaries (172.33.0.0/16, 192.169.1.0/24, and 11.0.0.0/8 are all public IPv4 ranges).
Addresses outside the three defined blocks are globally routable public addresses.

Key Concept

RFC 1918 Private IPv4 Address Ranges
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Topics

Private IPv4 Addressing and RFC 1918

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