VLSM (Variable Length Subnet Mask)

    Before diving into hands-on networking practice, I want to document what I’ve learned so far about VLSM, based on my current understanding. I assume that you already understand the basics of IP addresses and subnetting.

    VLSM is a method used to allocate IP addresses more efficiently by assigning subnet masks of different lengths based on the number of hosts required per subnet. This avoids wasting IP addresses and helps save router resources.

🔧 Why Use VLSM?

1. Without VLSM, every subnet might be given the same size (e.g., a /24 subnet, which provides 256 addresses), even if that many addresses aren’t needed. This leads to a lot of unused IPs.
2. With VLSM, you can assign just enough IPs to each department or network segment based on its actual needs.

🧠 Example:

Let’s say we have the following requirements:

1. Department 1 has 100 clients
2. Department 2 has 50 clients

Instead of assigning a /24 subnet (which gives 256 IPs) to each department, we can do better with VLSM:

1. Department 1: Needs at least 100 hosts → use a /25 subnet, which gives 128 IP addresses
2. Department 2: Needs at least 50 hosts → use a /26 subnet, which gives 64 IP addresses

This way:

1. You're using fewer IPs overall
2. The unused addresses can be used elsewhere
3. The router’s routing table becomes more optimized

✅ Benefits Recap:

1. Saves IP address space
2. Optimizes routing performance
3. Scales well for networks with segments of different sizes

Pretty easy right? Right? If you are bored, try to answer this:

Given the block 10.0.0.0/24, divide using VLSM for the following requirements:

Subnet A: 60 hosts

Subnet B: 30 hosts

Subnet C: 14 hosts

Give the network address, subnet mask, host range, and broadcast address for each subnet.