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BGP-Inter-Scenario 2

Overview

In BGP-Inter-Scenario 2, we implement a routing setup where routers from different autonomous systems (AS) exchange routes using BGP. The primary focus is on configuring AS-Path Prepending and Prefix Filtering as export policies, ensuring that:

  • AS-Path Prepending influences path selection by making certain routes less preferred.
  • Prefix Filtering ensures routers only advertise their own prefixes (such as /23 and /24) and do not act as transit routers for external traffic.

This scenario uses the following routers:

  • R1 (AS100) : Connected to R2 and R3, with specific policies applied for BGP route exports.
  • R2 (AS200) : Connected to R1 and R3, with appropriate OSPF and BGP configuration.
  • R3 (AS300) : Connected to R1 and R2, sharing routes between its own network and the other ASes.

BGP Policies Applied:

  1. Export Policy - AS-Path Prepending:
  • R1 applies AS-Path prepending when advertising routes to R2. This policy makes routes learned via R1 less preferred by adding extra AS numbers to the AS path, making it appear longer.
  1. Export Policy - Prefix Filtering:
  • R1 only exports its own prefixes (/23 and /24) and avoids advertising routes it learns from other routers. This policy prevents R1 from becoming a transit router for traffic between R2 and R3.

Topology

The topology includes the following interconnections between the routers:

  • R1 (AS100) ↔ R2 (AS200) via 10.10.1.0/24
  • R1 (AS100) ↔ R3 (AS300) via 10.10.2.0/24
  • R2 (AS200) ↔ R3 (AS300) via 10.10.3.0/24

Each router also has its own internal networks:

  • R1: 10.11.1.0/24
  • R2: 10.12.1.0/24
  • R3: 10.13.1.0/24

Testing

  1. AS-Path Prepending: You can verify the AS-path prepending by checking the BGP route advertisements from R1 to R2. R2 will receive the routes with additional AS numbers added by R1.
R2# show ip bgp neighbors 10.10.1.1 advertised-routes
  1. Prefix Filtering: On R3, you can confirm that it only receives prefixes directly from R1, without any transit prefixes being passed from R2.
R3# show ip bgp neighbors 10.10.2.1 advertised-routes
  1. OSPF: Each router will also have OSPF running within its own AS, ensuring internal communication. You can verify the OSPF configuration and routing table with:
R1# show ip ospf neighbor
R2# show ip ospf neighbor
R3# show ip ospf neighbor

Licencse

This project is licensed under the Creative Commons Legal Code CC0 1.0 Universal. See the LICENSE file for details.

Project Report (in Indonesian)

For more detailed information on the project setup, configuration, and results, refer to the full report:

Inter-Domain-Routing.pdf