Create a Subnet for 2000 IP Addresses
Question
You have a requirement to create a subnet which will have the ability to host 2000 addresses.
Which of the below network masks would you use to ensure that the ability to host this many IP addresses is as accurate as possible.
Answers
Explanations
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A. B. C. D.Answer - A.
You can use any CIDR calculator available online to see the number of subnets and host addresses when you use different network masks.
A snapshot of one such site is given below.
http://www.subnet-calculator.com/cidr.php
The number of IP addresses that can be hosted in a subnet is determined by the subnet's network mask. The network mask specifies how many bits of the IP address are used to identify the network and how many bits are used to identify the host.
In this case, we need to find a network mask that can accommodate 2000 IP addresses.
We know that an IP address is made up of 32 bits (IPv4). We also know that the first few bits of an IP address identify the network, and the remaining bits identify the host.
To determine the number of IP addresses that can be hosted in a subnet, we need to know how many bits are used to identify the host. This is calculated as follows:
2^(number of host bits) - 2
The "- 2" is because the first and last IP addresses in the subnet are reserved for the network address and broadcast address, respectively, and cannot be assigned to hosts.
So, let's try each of the network masks provided and calculate how many IP addresses they can accommodate:
A. /21
A /21 network mask would use 21 bits to identify the network and 11 bits to identify the host.
2^(11) - 2 = 2046
A /21 network mask can accommodate up to 2046 IP addresses. This is more than the required 2000, but it may be more than necessary and result in wasted IP addresses.
B. /22
A /22 network mask would use 22 bits to identify the network and 10 bits to identify the host.
2^(10) - 2 = 1022
A /22 network mask can accommodate up to 1022 IP addresses. This is less than the required 2000 and may not be enough.
C. /23
A /23 network mask would use 23 bits to identify the network and 9 bits to identify the host.
2^(9) - 2 = 510
A /23 network mask can accommodate up to 510 IP addresses. This is significantly less than the required 2000 and not sufficient.
D. /24
A /24 network mask would use 24 bits to identify the network and 8 bits to identify the host.
2^(8) - 2 = 254
A /24 network mask can accommodate up to 254 IP addresses. This is much less than the required 2000 and not sufficient.
Based on the above calculations, the network mask that would allow us to host 2000 IP addresses is a /21 network mask. However, if we want to be more conservative and avoid wasting IP addresses, we could use a /22 network mask.