In BGP-Inter-Scenario 1, we implement a routing setup where routers from different autonomous systems (AS) exchange routes using both OSPF for intra-domain routing and BGP for inter-domain routing. The topology used is similar to an OSPF setup but is modified to allow the border routers to also run BGP. The topology is divided into three ASNs: AS100 on R1, AS200 on R2, and AS300 on R3.
In this scenario, the following configurations are applied:
- Import Policy: Local Preference
- This policy is used to influence the routing decisions within an AS by assigning a higher preference to certain routes.
- Export Policy: AS-Path Prepending
- This policy is employed to manipulate the AS-Path attribute of advertised routes, making certain routes less preferred by adding the AS number multiple times to the path.
The routers are configured as follows:
- 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.
- Import Policy - Local Preference:
- R1 configures local preference to prioritize certain routes within its AS. By assigning a higher local preference to routes learned from R3, R1 influences the path selection for outbound traffic to R2, ensuring that the preferred routes are chosen when multiple options exist.
- 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.
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
- Local Preference: You can verify the local preference configuration by checking the BGP route advertisements on R2. R2 will prefer routes with a higher local preference set by R1.
R1# show ip bgp- AS-Path Prepending: To confirm the effect of AS-Path prepending, check the BGP route advertisements from R1 to R2. R2 will receive routes with additional AS numbers added by R1.
R1# show ip bgp neighbors 10.10.2.2 advertised-routesThis project is licensed under the Creative Commons Legal Code CC0 1.0 Universal. See the LICENSE file for details.
For more detailed information on the project setup, configuration, and results, refer to the full report: