Mastering IP address calculations - Part 1

Table of Contents

1. Introduction
2. Understanding IP Address and Subnet Mask
   • 2.1 Binary Representation of IP Address
   • 2.2 Binary Representation of Subnet Mask
3. Finding the Network Address
   • 3.1 Applying Bitwise AND Operation
   • 3.2 Converting Binary to Decimal
4. Finding the Broadcast Address
   • 4.1 Setting Host Bits to 1
   • 4.2 Converting Binary to Decimal
5. Finding the First Usable Host Address
   • 5.1 Setting the Last Host Bit to 1
   • 5.2 Converting Binary to Decimal
6. Finding the Last Usable Host Address
   • 6.1 Finding the Address before the Broadcast Address
   • 6.2 Converting Binary to Decimal
7. Calculating the Number of Usable Hosts
8. Conclusion

Understanding IP Address and Subnet Mask

In this tutorial, we will learn how to determine the network address, broadcast address, first usable host address, last usable host address, and the number of usable hosts within a network given an IP address and its subnet mask. Before we dive into the calculation process, let's understand the basics of IP addresses and subnet masks.

Binary Representation of IP Address

An IP address is a unique numerical label assigned to a host within a network. It consists of four portions, each represented by an eight-bit binary number. For example, the IP address 10.100.20.180 can be represented as 00001010.01100100.00010100.10110100 in binary.

Binary Representation of Subnet Mask

A subnet mask determines the network and host portions of an IP address. It also consists of four portions, represented by eight-bit binary numbers. For example, the subnet mask 255.255.255.240 can be represented as 11111111.11111111.11111111.11110000 in binary.

Finding the Network Address

The network address is the base address of a network to which a host belongs. To find the network address, we perform a bitwise AND operation on the binary representation of the IP address and the subnet mask.

Applying Bitwise AND Operation

By applying the bitwise AND operation between the IP address and the subnet mask, we get the network portion of the IP address. For example, let's consider the IP address 10.100.20.180 and the subnet mask 255.255.255.240. The binary representation of the IP address is 00001010.01100100.00010100.10110100, and the binary representation of the subnet mask is 11111111.11111111.11111111.11110000.

Performing the bitwise AND operation bit by bit, we get the network portion: 00001010.01100100.00010100.10110000.

Converting Binary to Decimal

To represent the network address in decimal format, we convert each portion of the binary address to its decimal equivalent. In this case, the converted network address is 10.100.20.176.

Finding the Broadcast Address

The broadcast address is the highest address in a network and is used to send data packets to all hosts within the network. To find the broadcast address, we set all the host bits in the IP address to 1.

Setting Host Bits to 1

The host bits in the IP address are those bits that differ from the subnet mask. By setting all host bits to 1, we get the broadcast address. Using the previous example, the binary representation of the IP address is 00001010.01100100.00010100.10110100.

Setting all the host bits to 1, we get the broadcast address: 00001010.01100100.00010100.10111111.

Converting Binary to Decimal

Converting the binary broadcast address to decimal format, we get 10.100.20.191.

Finding the First Usable Host Address

The first usable host address is the address immediately following the network address. It represents the first available IP address for a host within the network. To find the first usable host address, we change the very last host bit in the binary IP address to 1.

Setting the Last Host Bit to 1

By changing the last host bit to 1 in the binary IP address, we obtain the first usable host address. Continuing from the previous example, the binary representation of the IP address is 00001010.01100100.00010100.10110100.

Changing the very last host bit to 1, we get the first usable host address: 00001010.01100100.00010100.10110101.

Converting Binary to Decimal

Converting the binary first usable host address to decimal format, we get 10.100.20.181.

Finding the Last Usable Host Address

The last usable host address is the address immediately preceding the broadcast address. It represents the last available IP address for a host within the network. To find the last usable host address, we find the address before the broadcast address.

Finding the Address before the Broadcast Address

The address immediately before the broadcast address is obtained by changing the very last bit in the broadcast address from 1 to 0. Using the previous example, the binary broadcast address is 00001010.01100100.00010100.10111111.

Changing the very last bit to 0, we get the last usable host address: 00001010.01100100.00010100.10111110.

Converting Binary to Decimal

Converting the binary last usable host address to decimal format, we get 10.100.20.190.

Calculating the Number of Usable Hosts

The number of usable hosts within a network can be calculated by subtracting two from the total number of combinations possible with the host bits. In our example, we have 4 host bits, which allows for 16 combinations. However, two of these combinations are reserved for the network address and the broadcast address, leaving us with 14 usable hosts.

Conclusion

In this tutorial, we have learned how to determine the network address, broadcast address, first usable host address, last usable host address, and the number of usable hosts within a network given an IP address and its subnet mask. By performing bitwise operations and converting binary to decimal, we can easily identify and calculate these essential components of a network configuration.

Highlights

• Understanding binary representation of IP address and subnet mask.
• Calculating network address through bitwise AND operation.
• Finding the broadcast address by setting all host bits to 1.
• Determining the first and last usable host addresses.
• Calculating the number of usable hosts within a network.

FAQs

Q: What is the purpose of a subnet mask? A: A subnet mask is used to divide an IP address into network and host portions, allowing for efficient network management and addressing.

Q: How do I calculate the number of usable hosts within a network? A: Subtract two from the total number of combinations possible with the host bits to account for the reserved network and broadcast addresses.

Q: Can the network address and broadcast address be assigned to devices? A: No, the network address and broadcast address are not assignable to individual devices within a network.

Q: How do I find the last usable host address? A: The last usable host address is obtained by finding the address immediately before the broadcast address.

Q: What happens if I set all host bits to 0 instead of 1 for the broadcast address? A: Setting all host bits to 0 would result in a different address, which is not the correct broadcast address.