How Many Host Addresses Are Available On The 192.168.10.128/26 Network Simplified Subnetting Guide As I delve into the intricate world of networking for my IT course, there’s this one topic that consistently slips my mind, despite my understanding of the concept. I’ve found myself repeatedly scouring my notes and online resources, which has prompted me to compile this blog solely dedicated to subnetting. It’s a consolidation of all my resources and notes to refresh my memory whenever needed.
This blog is tailored for individuals keen on learning the step-by-step process of subnetting or those like me who require an occasional refresher. However, I must assume that you already possess knowledge of IP address classes, subnet masks, and network IDs.
Learning Objectives of this blog:
- Understand the concept of subnetting.
- Learn how to decipher CIDR notation.
- Determine the number of hosts and network ID when presented with an IP CIDR notation.
- Calculate the range of hosts and the broadcast IP address of an IP subnet.
What is Subnetting?
Subnetting entails dividing a network into two or smaller networks, referred to as subnets. The primary objectives of subnetting are to bolster security, optimize routing efficiency, and reduce the scope of the broadcast domain¹. While I won’t delve deeply into the advantages of subnetting here, you can explore them [here](insert link).
How Do We Subnet?
Subnetting involves splitting an IP network address’s host portion into two segments. In essence, we borrow bits from the host bits of an IP address and employ them as subnet bits. The number of bits borrowed depends on the number of subnets required.
Allow me to illustrate with an example: suppose you have an IP address with a network ID of 192.168.1.0, and you aim to divide it into 6 distinct networks. To achieve this, you need to borrow 3 bits from the 8 host bits to accommodate your 6 subnets. The formula for this is:
What is CIDR?
CIDR stands for Classless Inter-Domain Routing and is also known as classless or prefix-based addressing. It was introduced to address the shortcomings of Class-based addressing.
The classful system of allocating IP addresses was inefficient. Those requiring slightly more than 254 host addresses were allocated a class B address block with 65533 host addresses. CIDR was developed to eliminate the traditional concept of Class A, B, and C network addresses, enabling more efficient allocation of IP address space based on specific needs. For a more detailed explanation, refer to RFC 1517–1520.
CIDR Address Notation
You may have encountered an IP address that appears as follows: 192.168.190.9/18 or subnet masks that look like this: 255.255.192.0, which differs from the usual subnet mask of 255.255.255.0.
Your IP address comprises 32 bits. The “/18” signifies that 18 bits of this address pertain to your network part, leaving 14 bits for host addresses. Consequently, you can calculate the number of hosts as follows:
(Number of hosts) = 2^(32 – 18) – 2 (subtracting 2 because the first address is the network ID, and the last address is the Broadcast ID).
For instance, the common IP address you might encounter in your internal network is 192.168.10.32/24. This implies that 24 bits were allocated for the network part of the address, leaving 8 bits for host addresses. You can visualize this notation better with the diagram above.
Let’s consider another example: an IP address of 192.168.190.9/18. To determine the number of hosts, network ID, and subnet, take note that “/18” means 18 bits are designated for the network part, leaving 14 bits for host bits.
To calculate the network ID, sum up all 18 bits to obtain a network ID of 192.168.128.0. As for determining the subnet, use 18 bits set to all ones (11111111) to identify the subnet.
It’s important to note that this method is designed to enhance your understanding of CIDR. If you seek a faster subnetting method, I recommend watching Professor Messer’s video on the Seven Second Subnetting Process.
IP Subnet’s Range of Hosts and Broadcast IP Address
Let’s take the IP address 192.168.10.32/24 as an example. Suppose we require 3 subnetworks and borrow 2 bits from the remaining host bits. We can deduce that our first subnet is 192.168.10.128. Now, we need to learn how to determine the range of hosts within that subnetwork and its Broadcast IP address.