Question

Difficulty: MediumPrivate IPv4 Addressing and RFC 1918

A network administrator is documenting the RFC 1918 private IPv4 address space allocation for an enterprise network redesign. Match each RFC 1918 address block on the left with its corresponding CIDR prefix length and block composition description on the right.

  • 10.0.0.0 – 10.255.255.255/8 prefix length comprising 1 Class A network block
  • 172.16.0.0 – 172.31.255.255/12 prefix length comprising 16 contiguous Class B network blocks
  • 192.168.0.0 – 192.168.255.255/16 prefix length comprising 256 contiguous Class C network blocks

Answer

10.0.0.0 – 10.255.255.255 matches '/8 prefix length comprising 1 Class A network block'; 172.16.0.0 – 172.31.255.255 matches '/12 prefix length comprising 16 contiguous Class B network blocks'; 192.168.0.0 – 192.168.255.255 matches '/16 prefix length comprising 256 contiguous Class C network blocks'.
Each RFC 1918 private IPv4 block aligns with a specific CIDR prefix and quantity of traditional classful networks: 10.0.0.0/8 represents one Class A block; 172.16.0.0/12 represents 16 contiguous Class B blocks (172.16.0.0 to 172.31.255.255); and 192.168.0.0/16 represents 256 contiguous Class C blocks (192.168.0.0 to 192.168.255.255).

Step-by-Step Solution

1
Identify the RFC 1918 Class A private address range
10.0.0.0 to 10.255.255.255 corresponds to 10.0.0.0/8 (1 Class A network).
RFC 1918 reserves the entire 10.0.0.0/8 network block for private IP addressing.
2
Identify the RFC 1918 Class B private address range
172.16.0.0 to 172.31.255.255 corresponds to 172.16.0.0/12, which spans 16 contiguous Class B networks (172.16.0.0/16 through 172.31.0.0/16).
A /12 prefix length allows 4 bits of subnetwork variation in the second octet (16 to 31), creating 16 Class B ranges.
3
Identify the RFC 1918 Class C private address range
192.168.0.0 to 192.168.255.255 corresponds to 192.168.0.0/16, which spans 256 contiguous Class C networks (192.168.0.0/24 through 192.168.255.0/24).
A /16 prefix length allows 8 bits of subnetwork variation in the third octet (0 to 255), creating 256 Class C ranges.

Key Concept

RFC 1918 Private IPv4 Address Space Specifications
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