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Hassam Fathe Muhammad
Hassam Fathe Muhammad

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Simulating an ISP Network with Cisco Packet Tracer (Hybrid Topology + OSPF)

#networking #cisco #ospf #simulation

🛠️ Tool Used

The tool CISCO Packet Tracer (CPT) is what I used to form an ISP-handed network of three topologies:

  • Bus topology
  • Tree topology
  • Star topology

Together, they form a hybrid topology.

🎯 Purpose

The idea of making such a simulation of an ISP network was to strengthen my knowledge and skills required to configure and study:

  • Real-world topologies
  • Routing methods & protocols
  • ISP systems

🗺️ Design Overview

  • A core router is used to connect to 3 routers, each representing one of the three topologies.
  • Routing from one LAN (topology) to another happens through routers.
  • This required an appropriate use of a routing algorithm such as OSPF.

🤔 Why I Used OSPF?

  • OSPF stands for Open Shortest Path First.
  • It’s an Internal Gateway Protocol (IGP) used for routing within a single autonomous system.
  • Routing could also be done manually (static routes), but that approach is not scalable or efficient.
  • OSPF provided automation, scalability, and a well-defined configuration method. 
Router> enable
Router# configure terminal
Router(config)# router ospf 1
Router(config-router)# network 10.0.0.0 0.0.0.255 area 0
Router(config-router)# network 192.168.1.0 0.0.0.255 area 0
Router(config-router)# end
Router# show ip ospf neighbor
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🌍 Simulating the Internet

  • The ISP data center can be expanded with servers, DNS servers (cache servers), and other devices.
  • In reality, the internet is a network of ISPs connected together.
  • To simulate this, I added another router (Global Router) to represent the internet connection with the ISP.

📚 What I Learned

Designing and configuring this project felt like engineering a small-scale ISP.

I learned about:

  • Routing protocols (like OSPF)
  • Routers’ ability to store and use neighboring routers’ addresses for routing
  • DHCP usage for handling private/topological devices 
Router(config)# ip dhcp excluded-address 192.168.1.1 192.168.1.10
Router(config)# ip dhcp pool LAN_POOL
Router(dhcp-config)# network 192.168.1.0 255.255.255.0
Router(dhcp-config)# default-router 192.168.1.1
Router(dhcp-config)# dns-server 8.8.8.8
Router(dhcp-config)# exit
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  • DNS servers for routing HTTP requests to web servers placed on the “global internet” (simulated search engines, since Packet Tracer doesn’t support real web apps/frameworks)

💭 Final Thoughts

This was a great learning experience — a foundational design and configuration setup for me to explore more complex systems and simulations in Computer Communications & Networking.

🤝 Over to You

Have you ever built a network simulation in Packet Tracer or GNS3?

Which routing protocols did you use — OSPF, RIP, BGP?

Share your experience in the comments 👇

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