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Difficulty: MediumPrivate IPv4 Addressing and RFC 1918

A network auditing tool generates a report listing IPv4 addresses detected on internal branch office node interfaces. Which of the following IPv4 addresses are compliant with RFC 1918 private IP addressing standards? (Select TWO.)

  1. 10.254.1.50Answer
  2. 172.29.40.10Answer
  3. C
    172.33.1.1
  4. D
    192.169.50.25

Answer

The IPv4 addresses 10.254.1.50 and 172.29.40.10 are valid RFC 1918 private IPv4 addresses.
The addresses 10.254.1.50 and 172.29.40.10 fit directly inside the RFC 1918 standard private ranges: 10.0.0.0/8 (10.0.0.0 to 10.255.255.255) and 172.16.0.0/12 (172.16.0.0 to 172.31.255.255) respectively.

Step-by-Step Solution

1
Recall the three designated 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).
Establishing accurate range boundaries is necessary to differentiate private non-routable IPs from public IPs.
2
Evaluate candidate address 10.254.1.50 against the RFC 1918 specifications.
10.254.1.50 begins with 10 in the first octet, making it a valid member of the 10.0.0.0/8 block.
Any IP starting with 10.x.x.x is private under RFC 1918.
3
Evaluate candidate address 172.29.40.10 against the RFC 1918 specifications.
172.29.40.10 has a second octet of 29, which lies within the inclusive 16–31 range for the 172.16.0.0/12 block.
Addresses from 172.16.0.0 through 172.31.255.255 are valid private addresses.
4
Evaluate invalid candidate addresses 172.33.1.1 and 192.169.50.25.
172.33.1.1 falls outside the 172.16–172.31 range, and 192.169.50.25 falls outside the 192.168.0.0/16 range.
Both 172.33.x.x and 192.169.x.x are public IPv4 addresses assigned on the Internet.

Key Concept

RFC 1918 Private IPv4 Address Scope
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Topics

Private IPv4 Addressing and RFC 1918

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