Free CCNA | Subnetting (VLSM) | Day 15 Lab | CCNA 200-301 Complete Course

Introduction

In this tutorial, we will explore how to subnet a Class C network using Variable Length Subnet Masking (VLSM). This is an essential skill for anyone preparing for the CCNA 200-301 certification, as it helps optimize IP address allocation within networks. By the end of this guide, you will understand how to apply VLSM to create efficient subnet designs for various LANs.

Step 1: Understand the Basics of VLSM

• VLSM allows for different subnet masks within the same network address, enabling more efficient use of IP addresses.
• It is particularly useful in scenarios where different subnets require varying numbers of IP addresses.
• Familiarize yourself with the binary representation of IP addresses and subnet masks, as this will be crucial for subnetting.

Step 2: Identify Network Requirements

• Determine the number of subnets and hosts required for each LAN. For example:
  • LAN 1: 20 hosts
  • LAN 2: 10 hosts
  • LAN 3: 5 hosts
  • LAN 4: 2 hosts
• Consider future growth to avoid needing to readdress your network soon after implementation.

Step 3: Calculate Subnet Masks

• Start with the Class C default subnet mask of 255.255.255.0 (or /24).
• Use the following calculations to determine the appropriate subnet masks for each LAN:
  • For 20 hosts: /27 (255.255.255.224) provides 30 usable addresses.
  • For 10 hosts: /28 (255.255.255.240) provides 14 usable addresses.
  • For 5 hosts: /29 (255.255.255.248) provides 6 usable addresses.
  • For 2 hosts: /30 (255.255.255.252) provides 2 usable addresses.

Step 4: Assign Subnet Addresses

• Begin with the first available address in your Class C network. For example, if you have the network 192.168.1.0:
  • Assign LAN 1: 192.168.1.0/27
  • Assign LAN 2: 192.168.1.32/28
  • Assign LAN 3: 192.168.1.48/29
  • Assign LAN 4: 192.168.1.56/30
• Ensure that each subnet is allocated without overlap and that you are utilizing the available address space efficiently.

Step 5: Configure Static Routes

• Once the subnets are assigned, configure static routes for communication between LANs if necessary.
• Use commands in a Cisco router to set static routes. For example:

  ip route 192.168.1.32 255.255.255.224 [next-hop address]
  ip route 192.168.1.48 255.255.255.240 [next-hop address]
  ip route 192.168.1.56 255.255.255.248 [next-hop address]
  

• Replace [next-hop address] with the appropriate next-hop IP for your network setup.

Conclusion

By following these steps, you have successfully subnetted a Class C network using VLSM, ensuring efficient address allocation for multiple LANs. As you continue your CCNA studies, practice these concepts with various scenarios to strengthen your subnetting skills. For further learning, consider exploring Packet Tracer labs to simulate and visualize your subnetting configurations.