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Difficulty: MediumIPv4 Addressing and Subnetting

A network administrator is designing a subnetwork scheme for a branch facility assigned the IPv4 block 192.168.16.0/22192.168.16.0/22. The design requirement specifies creating subnets that can each support a minimum of 5050 usable host IP addresses for individual department segments while maximizing the total number of subnets created. Which CIDR prefix length meets these requirements, and what is the exact number of usable host IP addresses provided per subnet?

  1. /26/26 prefix length providing 6262 usable host addressesAnswer
  2. B
    /26/26 prefix length providing 6464 usable host addresses
  3. C
    /25/25 prefix length providing 126126 usable host addresses
  4. D
    /27/27 prefix length providing 3030 usable host addresses

Answer

The /26/26 prefix length providing 6262 usable host addresses
To accommodate at least 5050 usable host IP addresses per subnet, the minimum number of host bits hh needed is 66, because 26−2=62≥502^6 - 2 = 62 \ge 50. Subtracting 66 host bits from 3232 gives a /26/26 prefix. The usable host count is 6262 after subtracting the network and broadcast addresses.

Step-by-Step Solution

1
Determine the required number of host bits (hh).
h=6h = 6 bits, since 26−2=62≥502^6 - 2 = 62 \ge 50.
Five host bits (25−2=302^5 - 2 = 30) would not provide enough IP addresses, while six bits provides sufficient capacity.
2
Calculate the CIDR prefix length.
Prefix length is 32−6=/2632 - 6 = /26.
Subtracting the host bits from the 32-bit total IPv4 address length yields the subnet prefix length.
3
Calculate the usable host count per subnet.
26−2=622^6 - 2 = 62 usable host IP addresses.
The network address (all host bits 0) and broadcast address (all host bits 1) cannot be assigned to hosts.

Key Concept

IPv4 Subnetting and Usable Host Calculation
Estimated Time:1m 30s
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Topics

IPv4 Addressing and Subnetting

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