VLSM Calculator

Base IP Address

Base Prefix

Required Hosts (Comma-separated, e.g., 50, 20, 10, 2)

Subnet Name	Requested	Allocated	Network/CIDR	Usable Range

How to Use the VLSM Subnet Calculator

Variable Length Subnet Masking (VLSM) allows network administrators to divide an IP address space into subnets of different sizes. Unlike traditional subnetting, which forces all subnets to have the same number of hosts, VLSM optimizes IP allocation by tailoring the subnet mask to the specific requirements of each local area network (LAN).

Step-by-Step Guide:

Step 1: Enter your major network IP address (e.g., 192.168.1.0) and its original CIDR notation (e.g., /24).
Step 2: Input the required number of hosts for each of your subnets, starting with the largest requirement first.
Step 3: Click "Calculate" to generate your routing table, which will display the Network ID, Broadcast Address, and Usable IP Range for each segment.

Why is this important for CCNA?

Mastering subnet calculations is critical for routing protocols and minimizing IP waste. Whether you are configuring a small branch office or a massive enterprise routing topology in Cisco Packet Tracer, accurate VLSM calculations ensure that your routers can communicate efficiently without IP overlaps.