Notes on Subnetting a Subnet (VLSM)

Key Concepts

• Subnetting a Subnet: Yes, it's possible to create subnets of different sizes from a single subnet.
• VLSM (Variable Length Subnet Mask): Allows for subnetting based on different host requirements.

Scenario Overview

• Given Network: 172.21.42.0/24
• Requirement: Create four networks for:
  • Guest
  • Robots
  • Servers
  • Workers
• Host Requirements:
  • Workers: 117 hosts
  • Robots: 57 hosts
  • Servers: 26 hosts
  • Guests: Remaining hosts

Total Hosts Calculation

• Total required hosts = 117 (Workers) + 57 (Robots) + 26 (Servers) + Guests = 210 hosts
• Given network (slash 24) can accommodate 253 hosts.

Subnetting Process

1. Start with Largest Requirement:

   • Workers (117 hosts) = Needs 7 host bits.
   • New subnet mask: /25 (255.255.255.128)
   • Network range: 172.21.42.0 - 172.21.42.127

2. Next Largest Requirement:

   • Robots (57 hosts) = Needs 6 host bits.
   • New subnet mask: /26 (255.255.255.192)
   • Network range: 172.21.42.128 - 172.21.42.191

3. Next Requirement:

   • Servers (26 hosts) = Needs 5 host bits.
   • New subnet mask: /27 (255.255.255.224)
   • Network range: 172.21.42.192 - 172.21.42.223

4. Final Requirement:

   • Guests = Remaining hosts after allocating to other networks.
   • New subnet mask: /28 (255.255.255.240)
   • Network range: 172.21.42.224 - 172.21.42.239

Summary of Subnet Ranges

• Workers: 172.21.42.0/25
• Robots: 172.21.42.128/26
• Servers: 172.21.42.192/27
• Guests: 172.21.42.224/28

Conclusion

• Successfully subnetted a /24 network into different sized subnets according to host requirements.
• VLSM is an effective method to conserve IP addresses and meet specific network needs.
• Continuous practice is essential to retain subnetting skills.

Resources for Further Study

• Boson Software: Excellent for practice exams and simulation tools.
• Network Chuck Academy: Extra practice questions and resources for subnetting and networking concepts.