Appropriate Subnet Masks for IP Address Configuration

A server technician is configuring the IP address on a newly installed server.

The documented configuration specifies using an IP address of 10.20.10.15 and a default gateway of 10.20.10.254

Which of the following subnet masks would be appropriate for this setup?

A.

255.255.255.0

B.

255.255.255.128

C.

255.255.255.240

D.

255.255.255.254

D.

https://www.calculator.net/ip-subnet-calculator.html?cclass=any&csubnet=30&cip=10.20.10.15&ctype=ipv4&printit=0&x=57&y=17

To determine the appropriate subnet mask for the given IP address and default gateway, we need to first understand the concept of subnetting. Subnetting is the process of dividing a larger network into smaller subnetworks or subnets. Each subnet has its own unique network address and range of host addresses.

The subnet mask is a 32-bit value that is used to divide an IP address into network and host portions. It determines how many bits are used for the network portion and how many are used for the host portion. The subnet mask is represented using four octets, each containing 8 bits.

To calculate the subnet mask, we need to know the number of bits used for the network portion of the address. This is determined by the number of subnets required and the number of hosts per subnet. In this case, we have been given a specific IP address and default gateway, so we can use these values to calculate the subnet mask.

The IP address is 10.20.10.15, which is a Class A private IP address. This means that the first octet is used for the network portion and the remaining three octets are used for the host portion.

The default gateway is 10.20.10.254, which is also in the same network as the IP address. This means that the network portion of the IP address and the default gateway is the same, which is 10.20.10.

To determine the appropriate subnet mask, we need to determine the number of bits used for the network portion. We can do this by converting the IP address and default gateway to binary and comparing them.

The IP address in binary is:

00001010 00010100 00001010 00001111

The default gateway in binary is:

00001010 00010100 00001010 11111110

By comparing these values, we can see that the first 24 bits are the same (10.20.10), which means that we need to use a subnet mask that has 24 bits for the network portion.

The subnet mask is represented using four octets, each containing 8 bits. To represent 24 bits, we need to use the first three octets (24 bits) and set the fourth octet to 0. The appropriate subnet mask in this case is therefore:

11111111 11111111 11111111 00000000

In dotted decimal notation, this is:

255.255.255.0

Therefore, the correct answer is option A.

Note: Option D, 255.255.255.254, is not a valid subnet mask because it only allows for two hosts per network (the network address and the broadcast address), which is not enough for a typical network setup.