Examkin

Question

Difficulty: Very hardPrivate IPv4 Addressing and RFC 1918

A network administrator is auditing enterprise IP addressing schemas across multiple branch office subnets to ensure full compliance with RFC 1918 private addressing standards. During the audit, the administrator observes four host interface configurations:

- Device A: 10.255.250.1/810.255.250.1/8
- Device B: 172.31.255.1/12172.31.255.1/12
- Device C: 172.32.10.1/16172.32.10.1/16
- Device D: 192.168.255.1/16192.168.255.1/16

Which host is configured with a globally routable public IPv4 address rather than a valid RFC 1918 private IPv4 address?

  1. Device C (172.32.10.1/16172.32.10.1/16)Answer
  2. B
    Device B (172.31.255.1/12172.31.255.1/12)
  3. C
    Device A (10.255.250.1/810.255.250.1/8)
  4. D
    Device D (192.168.255.1/16192.168.255.1/16)

Answer

Device C (172.32.10.1/16172.32.10.1/16) is configured with a public IPv4 address because RFC 1918 defines the Class B private IPv4 allocation strictly as 172.16.0.0172.16.0.0 to 172.31.255.255172.31.255.255 (172.16.0.0/12172.16.0.0/12).
The RFC 1918 standard reserves three specific IPv4 address blocks for private internal network use: 10.0.0.0/810.0.0.0/8 (10.0.0.010.0.0.0–10.255.255.25510.255.255.255), 172.16.0.0/12172.16.0.0/12 (172.16.0.0172.16.0.0–172.31.255.255172.31.255.255), and 192.168.0.0/16192.168.0.0/16 (192.168.0.0192.168.0.0–192.168.255.255192.168.255.255). The address assigned to Device C (172.32.10.1/16172.32.10.1/16) falls outside the 172.16.0.0/12172.16.0.0/12 boundary because its second octet (3232) is greater than 3131. Therefore, it is a globally routable public address.

Step-by-Step Solution

1
Identify the three defined RFC 1918 private IPv4 address blocks and their prefix boundaries.
Class A: 10.0.0.0/810.0.0.0/8 (10.0.0.010.0.0.0 – 10.255.255.25510.255.255.255); Class B: 172.16.0.0/12172.16.0.0/12 (172.16.0.0172.16.0.0 – 172.31.255.255172.31.255.255); Class C: 192.168.0.0/16192.168.0.0/16 (192.168.0.0192.168.0.0 – 192.168.255.255192.168.255.255).
RFC 1918 reserves specific IPv4 address ranges exclusively for private enterprise networks.
2
Evaluate each given IP address against the defined RFC 1918 boundaries.
10.255.250.110.255.250.1 is within 10.0.0.0/810.0.0.0/8; 172.31.255.1172.31.255.1 is within 172.16.0.0/12172.16.0.0/12; 192.168.255.1192.168.255.1 is within 192.168.0.0/16192.168.0.0/16; 172.32.10.1172.32.10.1 exceeds the upper limit (172.31.255.255172.31.255.255) of the Class B range.
Addresses beyond 172.31.255.255172.31.255.255, such as 172.32.0.0/11172.32.0.0/11, are allocated as public IP space by IANA.
3
Determine which device uses a public, globally routable IPv4 address.
Device C (172.32.10.1/16172.32.10.1/16) uses a public address.
Because 172.32.10.1172.32.10.1 is outside the RFC 1918 private boundary, it requires direct public Internet routing or dynamic translation.

Key Concept

RFC 1918 Private IPv4 Address Ranges
Rate this question

Topics

Private IPv4 Addressing and RFC 1918

More questions from this topic