ospf-bgp-network-lab

OSPF + BGP simulation in GNS3 (VyOS) with redistribution, default routing, and failover validation.

This project demonstrates how OSPF (Interior Gateway Protocol) and BGP (Exterior Gateway Protocol) work together in a network.
I built the lab in GNS3 using VyOS routers, designed a 4-router OSPF backbone, and configured eBGP sessions with external ISP routers.
The project covers route redistribution, default route propagation, and failover testing.

Project Overview

• Goal: Understand and implement OSPF + BGP routing in a simulated environment.
• Tools: GNS3, VyOS (community router), Linux.
• Key Features:
  • OSPF Area 0 backbone with 4 routers (R1–R4)
  • eBGP sessions with external ISPs (R5, R6)
  • Route redistribution between OSPF and BGP
  • Default route advertisement
  • Failover and convergence testing

Topology

IP Addressing Plan

Link / Interface	IP / Mask	AS Number	Notes
R1–LAN-A	10.10.10.1/24	65000	Customer LAN-A
R4–LAN-B	10.20.20.1/24	65000	Customer LAN-B
R1–R2	192.0.2.0/30	65000	OSPF Backbone
R2–R3	192.0.2.4/30	65000	OSPF Backbone
R3–R4	192.0.2.8/30	65000	OSPF Backbone
R1–R5 (ISP-A)	203.0.113.0/30	65100	eBGP to ISP-A
R4–R6 (ISP-B, optional)	203.0.113.4/30	65200	eBGP to ISP-B

Configuration Steps

Each router was configured using VyOS CLI. Full configs are saved in the /configs folder.
Below are highlights:

R1 (Customer Edge)

set system host-name R1
set interfaces ethernet eth0 address 192.0.2.1/30     # to R2
set interfaces ethernet eth2 address 10.10.10.1/24    # LAN-A
set interfaces ethernet eth3 address 203.0.113.1/30   # to ISP-A

# OSPF
set protocols ospf area 0 network 192.0.2.0/30
set protocols ospf area 0 network 10.10.10.0/24

# BGP
set protocols bgp 65000 neighbor 203.0.113.2 remote-as 65100
set protocols bgp 65000 network 10.10.10.0/24
set protocols static route 0.0.0.0/0 next-hop 203.0.113.2
set protocols ospf redistribute static

Similar configurations were applied to R2, R3, R4, R5, and R6. Full versions are available in the /configs folder.

Validation and Testing

To confirm that the OSPF and BGP configuration worked as intended, I performed the following checks:

OSPF Neighbors

I used the show ip ospf neighbor command. The output confirmed that R1–R2, R2–R3, and R3–R4 formed full OSPF adjacencies, ensuring all internal routers were properly connected.

BGP Summary

I ran show ip bgp summary. The output showed that R1 successfully established an eBGP session with R5 (ISP-A), and R4 established a session with R6 (ISP-B).

End-to-End Connectivity

I ran ping 10.20.20.1 to verify connectivity. This test confirmed that a host in LAN-A (10.10.10.0/24) could successfully reach LAN-B (10.20.20.0/24) through the OSPF backbone and BGP edges.

Failure Test

I simulated a failure by shutting down the R2–R3 link. Packet loss occurred briefly, and then OSPF quickly rerouted traffic through the alternate path. This demonstrated the resiliency and convergence of the design. Screenshots of the test results are available in the /screenshots folder.

Results and Learnings

• Connected LAN-A (10.10.10.0/24) to LAN-B (10.20.20.0/24) through the OSPF backbone and eBGP edge connections.
• Observed how OSPF builds adjacencies and reconverges when links fail, showcasing its high availability features.
• Successfully advertised customer prefixes into BGP and validated external reachability through ISP peers.
• Propagated a default route into OSPF for full network reachability.
• Gained practical experience in how routing protocols contribute to high availability and resilience in production networks.

Repository Structure

ospf-bgp-network-lab/
├── README.md # Project documentation, including an overview, validation steps, and key learnings.
├── diagrams/ # Network topology diagrams.
│ └── topology.png # A visual representation of the network setup.
├── configs/ # Router configurations (R1–R6) in plain text format.
├── screenshots/ # Evidence of the validation tests, including CLI outputs of show commands and ping results.
└── notes/ # Additional notes and observations made during the project.

Prerequisites

• GNS3 installed on your system
• VyOS ISO added as a router VM in GNS3
• Basic understanding of routing protocols (OSPF, BGP)

How to Reproduce

1. Install GNS3.
2. Download the VyOS ISO and add it as a router VM in GNS3.
3. Build the topology as shown in diagrams/topology.png.
4. Apply the configurations from the /configs folder to each router.
5. Run validation tests (ping, traceroute, show ip ospf, show ip bgp) to confirm connectivity and network behavior.

Future Improvements

• Add BFD (Bidirectional Forwarding Detection) for faster OSPF/BGP failure detection
• Implement route summarization to reduce routing table size
• Secure OSPF and BGP sessions with authentication (MD5)
• Automate configuration deployment using Python (Netmiko) or Ansible

License

This project is released under the MIT License.