Computer Science - Networking - Discussion

To accommodate the current and future subnets while allowing the largest possible number of host IDs per subnet, you need a subnet mask that provides a large number of available IP addresses for each subnet.

In this case, you have a Class A network address 10.0.0.0 and want to create 100 (40 current + 60 new) subnets.

To determine the appropriate subnet mask, you need to find the smallest subnet size that can accommodate the required number of subnets (100 in this case) and also provides a sufficient number of host addresses for each subnet.

The formula to find the number of subnets and hosts per subnet is as follows:

The number of subnets = 2^n.
Number of hosts per subnet = 2^(32-n) - 2.

Where "n" is the number of bits in the subnet mask.

Let's calculate for each option:

255.240.0.0(or/1)
Number of subnets = 2^12 = 4096.
Number of hosts per subnet = 2^(32-12) - 2 = 2^20 - 2 = 1,048,574 (approximately).

255.248.0.0 (or/13)
Number of subnets = 2^13 = 8192,
Number of hosts per subnet = 2^(32-13) - 2 = 2^19 - 2 = 524,286.

255.252.0.0 (or /14),
Number of subnets = 2^14 = 16,384.
Number of hosts per subnet = 2^(32-14) - 2 = 2^18 - 2 = 262,142.

255.254.0.0 (or /15),
Number of subnets = 2^15 = 32,768,
Number of hosts per subnet = 2^(32-15) - 2 = 2^17 - 2 = 131,070.

255.255.255.255 (or /32),
This is not a valid subnet mask for general use, as it represents a single IP address with no available host IDs for subnets.

Among the options, the best choice that allows for the largest possible number of host IDs per subnet while accommodating 100 subnets is option 1: 255.240.0.0.

This will provide approximately 1,048,574 host addresses per subnet, which is the highest number compared to the other options.

2^n = Number of Subnets where n is the number of masked on (1) bits in the subnet mask
now a number of Subnets are 60 + 40 = 100.

So, 2^n = 100, solving for n = log 100 /log 2
n=6.6 approximately n = 7

Thus Since the network address is in Class A, so the subnet bits will be in The 2nd eight bits of IP address with 7on bits and 1off bits.

The 1st eight bits will be all on.i.e 11111111 or 255, the 2nd eight bits will be 111111110 or 254 the rest will be 0's.

So the answer will be 255.254.0.0 subnet mask or D.

40 subnets + 60 subnets = 100 subnets required.
2^7= 128 which is nearer to 100 subnets.
We know : 1= 128
2= 192
3= 224
4= 240
5= 248
6= 252
7= 254
8= 256
So, Subnet mask will be : 255. 254.0.0.

Agree with Wasimuddin & Sandeep Sanmani.
10.0.0.0 is represented in binary as
0000 1010.0000 0000.0000 0000.0000 0000
Sandeep has explained it clearly.Initially Network address was 10.0.0.0/8 & after creating provision for 100 subnets:
Subnet-0 Network Address= 10.0.0.0/15
Subnet-1 Network Address= 10.1.0.0/15
..
..
..

First of all, we should know what is subnetting -it is a process in which we decide the subnet mask into parts and for that purpose, we have to convert last bit of network(1's) id in to host(0"s) id.

11111111 11111111 00000000 00000000

After converting.

11111111 11111110 00000000 00000000

As we need 100 subnets which is greater than 64 but less than 128 implies portion of IP address identifying no of subnet need at least 7 1's. Therefore subnet mask has at least 15 1's and at most 17 zeros. So max. number of host can be assign to this mask only. So subnet mask will be 255.254.0.0.

As we need 100 subnets which is greater than 64 but less than 128 implies portion of IP address identifying no of subnet need at least 7 1's. Therefore subnet mask has at least 15 1's and at most 17 zeros. So max. number of host can be assign to this mask only. So subnet mask will be 255.254.0.0.

In 10.0.0.0 , 10 will remain fixed, we need to create 100 subnets, we will require at least 7 bits to uniquely identify each subnet (2^7 = 128 which is > 100),
So in this;
10.(00000000).00000000.00000000, starting 7 bits will be chosen,
i.e., -
10.(11111110).00000000.00000000 = 10.254.0.0.

Option A gives us the most number of host. reason: 255.240.0.0 subnet mask gives 11111111.11110000.00000000.00000000 . The host bits is zero while the subnet bit is 1. 2 to the power 12 equals number of subnet while 2 to the power 20 minus 2 gives us the number of host per subnet.

Required network = 100.

Available bits are = 32 bits.

Network id for class A = 10(block 1). 0(block 2). 0(block 3). 0(block 4).

So to create 100 subnet, we require 7 bits of block 2 and extra 1 bit we can use for host id.

So subnet mask will be (255-1) = 254!