A network technician is configuring an interface on a router for a subnet assigned the /28… — CompTIA Network+

A network technician is configuring an interface on a router for a subnet assigned the $/28$ CIDR prefix. Which of the following statements regarding this subnet prefix are correct? (Select TWO.)

The subnet mask in dotted-decimal notation is $255.255.255.240$ .Answer
The total number of usable host IP addresses available on the subnet is 14.Answer
C
The total number of usable host IP addresses available on the subnet is 16.
D
The subnet mask in dotted-decimal notation is $255.255.255.224$ .

Answer

The statement that the subnet mask in dotted-decimal notation is 255.255.255.240 and the statement that the total number of usable host IP addresses is 14 are correct.

For a

/28

prefix,

28

bits belong to the network identifier, leaving

4

host bits (

32 - 28 = 4

). In dotted-decimal notation, 28 mask bits translate to

255.255.255.240

because

128 + 64 + 32 + 16 = 240

. The usable host capacity is calculated using the formula

2^h - 2 = 2^4 - 2 = 14

Step-by-Step Solution

Calculate the subnet mask in dotted-decimal notation.

Prefix length

/28

means 28 network bits and

32 - 28 = 4

host bits. The binary mask is `11111111.11111111.11111111.11110000`, which translates to

255.255.255.240

Converting CIDR prefix length to octets yields the dotted-decimal subnet mask.

Calculate the number of usable host IP addresses.

Total IP addresses =

2^4 = 16

. Usable host addresses =

2^4 - 2 = 14

The network address (all host bits 0) and the broadcast address (all host bits 1) cannot be assigned to individual hosts.

Key Concept

Subnet Mask Dotted-Decimal Conversion and Usable Host IP Calculation

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