This video explains the Longest Prefix Match (LPM) concept in IP routing and how it helps routers determine the most specific path for forwarding packets.
Key Takeaways:
- Problem Setup: Two servers (Server 30 & Server 60) on different sites cannot communicate due to routing issues.
- Routing Table Review: The firewall and ISP routers have general routes, but no specific paths for the servers.
- Applying Longest Prefix Match:
- Adding /32 static routes to explicitly define the path for each server.
- Ensuring packets take the correct next-hop gateway instead of default routes.
- Configuring ISP Routes: The ISP router needs static routes for both server networks to complete the path.
- Security Policies: Inbound rules are added on firewalls to allow communication between the servers.
- Troubleshooting Connectivity:
- Initial ping tests fail due to the servers treating the destination as a local network.
- Fix: Adding static routes directly on the servers to force traffic through the correct gateway.
- Final Test: After adjustments, connectivity between the servers is successful, demonstrating how LPM ensures proper packet forwarding.
Conclusion:
By using Longest Prefix Match, routers select the most specific route when multiple options exist, ensuring efficient and accurate packet delivery. This technique is essential for advanced networking, including firewall rules, VPNs, and internet routing.
