A company Bit-by-Bit Inc. has been assigned a network IP address of 155.1.0.0. I

Question

A company Bit-by-Bit Inc. has been assigned a network IP address of 155.1.0.0. It has three divisions that need a total of 85 subnets. You are the network administrator for the company and are responsible for creating the subnets. Please answer the following questions. How many bits do you need to borrow from the host bits for the subnet field? What is the maximum number of host addresses per subnet? What is the maximum number of IP addresses that can be assigned to a host device per subnet? What is the subnet mask in binary representation? What is the subnet mask in decimal representation? Please indicate the following details for the first three subnets and last possible subnet in the network:- a. Subnet number b. Subnet address c. Range of host addresses that can be assigned to a host device. d. Direct Broadcast address Can you assign the IP address 155.1.5.255 to a host device in the network?

Explanation / Answer

Subnetting : Subnetting is the process of creating new networks (or subnets) by stealing bits from the host portion of a subnet mask. There is one caveat: stealing bits from hosts creates more networks but fewer hosts per network.

1) Given IP address : 155.1.0.0 which belongs to Class B IP address (ranges 128-191).

So Subnet mask will be 255.255.0.0

We need to create 85 subnet mask .

Binary form of subnet mask : 255.255.0.0

11111111.11111111.0000000.00000000

For creating 85 subnet mask 26 =64 (which is not satisfied)

So we should steal 7 bits .i.e 27=128(85 belongs under this)

Hence 7 bits need to borrow from the host bits for subnet field.

Then subnet address will be 255.255.254.0

2) Remember : The subnet mask follows two rules:

• If a binary bit is set to a 1 (or on) in a subnet mask, the corresponding bit in the address identifies the network.

• If a binary bit is set to a 0 (or off) in a subnet mask, the corresponding bit in the address identifies the host.

Now To find maximum number of host addresses per subnet = 2n where n=number of bits in host

here n = 9 bits in host

so maximum number of host = 29 =512 hosts per network

3) Maximum number of IP addresses that can be assigned to a host device per subnet

= 2n - 2= 29 - 2 =512-2 =510 usable host per subnet

4) Subnet mask in Binary Representation :

11111111.11111111.0000000.00000000

After subnetting New subnet mask

11111111.11111111.11111110.00000000

5) Subnet Mask in Decimal Representation :

255.255.0.0

After Subnetting New Subnet Mask

255.255.254.0

6)

a) subnet number : Since New Subnet Address is 11111111.11111111.11111110.00000000 (255.255.254.0 CIDR notation) So subnet number will be 27 -2 =128-2=126

b) Subnet Address : 11111111.11111111.11111110.00000000 (255.255.254.0 CIDR notation)

c) Range of host Addresses : 155.1.0.1 ---155.1.0.254

d) Direct BroadCast Address : 155.1.255.255

7) We can not assign the IP addresss 155.1.5.255 to any host device in the network. because this is the last address of any subnet which is called Broadcast Address.

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