Identify the /30 subnetwork A host has IPv4 address 172.16.45.14/30. Which subnetwork does this host belong to when using a /30 mask on that class B private range?

Introduction / Context:
A /30 subnet provides exactly two usable host addresses, making it ideal for point-to-point links. To determine the correct network address for a given host, you must compute the block size and align the host's last octet to the network boundary for that block. This exercise reinforces fast mental math for subnetting in the field.

Given Data / Assumptions:

• IP address: 172.16.45.14.
• Prefix length: /30 (mask 255.255.255.252).
• We are interested in the precise subnetwork (network ID).

Concept / Approach:

The /30 mask means the block size in the last octet is 4 (256 - 252 = 4). Valid network boundaries occur at multiples of 4: .0, .4, .8, .12, .16, etc. Each block of 4 addresses consists of network, two usable hosts, and broadcast. We must find the multiple of 4 that is less than or equal to 14 and whose next boundary is 16; that network is .12 and its range is .12–.15.

Step-by-Step Solution:

Verification / Alternative check:

Binary check: AND 14 with mask 252 (11111100) yields 12 (00001100), confirming the network is .12. A quick lab ping between .13 and .14 would succeed with mask /30 and the broadcast observed at .15.

Why Other Options Are Wrong:

• .0, .4, .8, .16 are valid /30 boundaries, but .14 does not fall inside those networks except .12–.15.

Common Pitfalls:

• Using /29 math (block size 8) by mistake.
• Confusing broadcast with network address when the host is near the top of the block.

Final Answer:

172.16.45.12