Lesson 38: Calculating Subnets: Step-by-Step Example 1 (/26)

Let's apply binary math to calculate subnetting for the network 192.168.1.0/26.

Step 1: Determine Network and Host Bits

• Total Bits: 32
• Network Bits (N): The prefix is /26. (26 bits are dedicated to the network)
• Host Bits (H): 32 - 26 = 6 bits remain for the hosts.

Step 2: Calculate Subnets and Hosts

• Borrowed Bits (S): Since /24 (255.255.255.0) is the default Class C boundary, we borrowed $26 - 24 = 2$ bits.
• Number of Subnets: $2^S = 2^2 = 4$ subnets.
• Usable Hosts per Subnet: $2^H - 2 = 2^6 - 2 = 64 - 2 = 62$ usable hosts.

Step 3: Determine the Block Size (Magic Number)

In the fourth octet, the 26th bit is the 2nd borrowed bit. The value of this bit determines the block size or subnet increment.

• The 26th bit has a value of 64. This is the block size.

Step 4: List the Subnets

Starting from the base network, increment by the block size (64) until you reach 256:

Conclusion: Subnetting is merely controlled manipulation of the subnet mask to divide the network space efficiently.