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Difficulty: MediumIPv4 Addressing and Subnetting

An enterprise network engineer is provisioning an isolated management subnet using the IPv4 block 10.150.80.0/2310.150.80.0/23. Out of the total usable host IP addresses in this subnet, 55 IP addresses are statically reserved for gateway redundancy protocols and infrastructure monitoring agents. How many usable host IP addresses remain available for assignment to endpoint workstations in this subnet?

Answer: 505 addresses

Answer

The total number of usable host IP addresses remaining available for endpoint workstations is 505.
A /23 CIDR prefix allocates 9 bits for host addressing, yielding 29=5122^9 = 512 total IP addresses. Subtracting 2 addresses for the network ID and broadcast address leaves 510 usable host IP addresses. Deducting the 5 statically reserved infrastructure addresses results in 505 remaining usable host addresses for endpoint workstations.

Step-by-Step Solution

1
Calculate the total IP address capacity of a /23 prefix block.
A /23 subnet contains 232−23=29=5122^{32 - 23} = 2^9 = 512 total IP addresses.
The prefix length of /23 leaves 9 bits available for host addressing.
2
Subtract the non-assignable network ID and broadcast address.
512−2=510512 - 2 = 510 standard usable host IP addresses.
The first address in the block is the network identifier and the last address is the subnet broadcast address.
3
Deduct the statically reserved IP addresses from the usable host pool.
510−5=505510 - 5 = 505 host IP addresses remaining.
Five addresses are designated for gateway redundancy and monitoring infrastructure, leaving 505 addresses for workstations.

Key Concept

IPv4 Subnet Usable Host Calculation with Infrastructure Reservations
Estimated Time:1m 30s
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Topics

IPv4 Addressing and Subnetting

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