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Difficulty: MediumIPv4 Addressing and Subnetting

An enterprise network administrator needs to design an IPv4 subnet for a new IP security camera deployment that must support 500 host devices. What is the maximum number of usable host IPv4 addresses provided by the smallest standard CIDR subnet block that can accommodate this requirement?

Answer: 510

Answer

510 usable host IPv4 addresses
To support 500 host devices, the number of host bits hh must satisfy 2h−2≥5002^h - 2 \ge 500. A /24/24 subnet (h=8h = 8) yields only 28−2=2542^8 - 2 = 254 usable hosts, which is insufficient. The smallest subnet size that meets the requirement is a /23/23 subnet (h=9h = 9), which provides 29−2=5102^9 - 2 = 510 usable host addresses.

Step-by-Step Solution

1
Determine the host bit requirement formula
Use 2h−2≥5002^h - 2 \ge 500, where hh represents host bits.
In every standard IPv4 subnet, two addresses are reserved: the network ID (all host bits 0) and the broadcast address (all host bits 1).
2
Calculate the smallest number of host bits that accommodates 500 hosts
28−2=2542^8 - 2 = 254 usable addresses (too small for 500 hosts); 29−2=5102^9 - 2 = 510 usable addresses (meets the requirement).
Selecting 9 host bits leaves 32−9=2332 - 9 = 23 network bits, resulting in a /23/23 prefix length.
3
Calculate the usable host capacity
29−2=512−2=5102^9 - 2 = 512 - 2 = 510 usable host addresses.
Subtracting 2 reserved addresses from the 512 total addresses gives 510 valid host assignments.

Key Concept

IPv4 Subnet Sizing and Usable Host Calculation
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Topics

IPv4 Addressing and Subnetting

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