A bank has the network block 192.168.10.0/24. The IT manager wants to divide this into 4 equal subnets. (a) How many bits do you need to borrow to make 4 subnets? (b) What is the new Subnet Mark in dotted-decimal format? (c) Write down the Network Address, the First Usable IP, and the Broadcast Address for the second subnet created. Show your calculation.

Given Data:

Network Block: 192.168.10.0/24
Number of required subnets = 4

(a) Bits needed to borrow to make 4 subnets:

To divide the network into subnets, we use the formula \(2^n \ge N\), where \(n\) is the number of bits borrowed from the host portion and \(N\) is the required number of subnets.

\(2^n \ge 4\)

\(2^2 = 4\)

Therefore, you need to borrow 2 bits.

(b) New Subnet Mask in dotted-decimal format:

Original CIDR prefix = /24
Bits borrowed = 2
New CIDR prefix = 24 + 2 = /26

In binary notation, a /26 mask has 26 subnet bits (1s) and 6 host bits (0s):
11111111.11111111.11111111.11000000

Converting the last octet into decimal format:
\(128 + 64 = 192\)

So, the new Subnet Mask is 255.255.255.192.

(c) Calculation for the 2nd Subnet:

Block Size (Magic Number) = \(256 - 192 = 64\) (or \(2^6 = 64\) addresses per subnet).

Subnet divisions with their address ranges:

  
• 1st Subnet: Network Address = 192.168.10.0, Usable IPs = 192.168.10.1 - 192.168.10.62, Broadcast Address = 192.168.10.63
  
• 2nd Subnet: Network Address = 192.168.10.64, Usable IPs = 192.168.10.65 - 192.168.10.126, Broadcast Address = 192.168.10.127
  
• 3rd Subnet: Network Address = 192.168.10.128, Usable IPs = 192.168.10.129 - 192.168.10.190, Broadcast Address = 192.168.10.191
  
• 4th Subnet: Network Address = 192.168.10.192, Usable IPs = 192.168.10.193 - 192.168.10.254, Broadcast Address = 192.168.10.255

Summary for the second subnet:

Network Address: 192.168.10.64
First Usable IP: 192.168.10.65
Broadcast Address: 192.168.10.127