A network administrator needs to assign an IPv4 subnet for a database cluster requiring st… — CompTIA Network+

A network administrator needs to assign an IPv4 subnet for a database cluster requiring static IP addresses for $110$ physical node interfaces, $2$ virtual load balancer IP addresses, and $2$ redundant default gateway interfaces. Which CIDR prefix length represents the smallest subnet mask that will accommodate all required host addresses?

/25Answer
B
/26
C
/24
D
/27

Answer

The smallest subnet mask in CIDR notation that accommodates all required addresses is /25.

The scenario requires allocating 114 usable IP addresses (

110 + 2 + 2 = 114

). A /25 subnet allocates 7 host bits, giving

2^7 = 128

total IP addresses. Subtracting 2 for the network ID and broadcast address results in 126 usable host IP addresses. This satisfies the 114 required addresses while using the smallest possible subnet block.

Step-by-Step Solution

Calculate total host IP addresses required

110 \text{ physical interfaces} + 2 \text{ load balancer virtual IPs} + 2 \text{ gateway interfaces} = 114 \text{ host IP addresses}

Every active physical interface, redundant gateway, and virtual IP assigned on the local subnet requires a unique usable IPv4 host address.

Determine required host bits (n) using formula 2^n - 2 >= required usable hosts

For

n = 6

2^6 - 2 = 62

usable host IPs (insufficient). For

n = 7

2^7 - 2 = 126

usable host IPs (sufficient for 114).

Subnet calculations must subtract 2 addresses (the Network ID and the Broadcast address) from the total pool of

2^n

addresses.

Calculate the CIDR prefix length

32 \text{ total IPv4 bits} - 7 \text{ host bits} = /25 \text{ prefix length}

Subtracting the number of host bits from the 32-bit total IPv4 address space yields the subnet prefix length.

Key Concept

Calculating usable IPv4 host capacity and determining optimal CIDR subnet mask allocation.

Estimated Time:1m 30s

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