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BGP Route Reflector

·451 words·3 mins
lab1918
Author
lab1918

The concept of a Route Reflector (RR) is used in the Border Gateway Protocol (BGP), which is the primary routing protocol used to exchange routing information across the Internet and large IP networks. The purpose of a route reflector is to overcome certain limitations of BGP, specifically related to the iBGP (internal BGP) full mesh requirement.

Background: iBGP Full Mesh Requirement
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  • In BGP, there’s a distinction between iBGP (internal BGP, used within an autonomous system) and eBGP (external BGP, used between different autonomous systems).
  • iBGP has a requirement that all iBGP routers within an autonomous system must form a full mesh of sessions with each other. This is because iBGP does not change the AS_PATH attribute and relies on the full mesh to prevent routing loops.
  • As the number of routers in a network increases, the full mesh requirement becomes impractical due to the quadratic increase in the number of required BGP sessions.

Purpose of a Route Reflector
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  1. Reduce the Number of BGP Sessions: The primary purpose of a route reflector is to reduce the number of BGP sessions in a network. It allows iBGP routers to have a full mesh of connections without requiring a direct peering relationship between every pair of routers.

  2. Simplify Network Configuration and Management: By reducing the number of required BGP sessions, route reflectors simplify network configuration and management, especially in large networks.

  3. Efficient Routing Information Propagation: Route reflectors help in efficient propagation of routing information within an autonomous system, ensuring that all routers are aware of available routes.

  4. Scalability: Route reflectors make scaling an autonomous system easier, as adding new routers does not exponentially increase the complexity of the BGP configuration.

How Route Reflectors Work
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  • Clients and Non-Clients: In a route reflector setup, iBGP routers are divided into clients and non-clients of the route reflector. Clients of a route reflector do not need to maintain iBGP sessions with each other, only with the route reflector.
  • Reflection of Routes: The route reflector reflects routes received from one client to all other clients and non-clients. This way, it bypasses the need for a full mesh.
  • Attributes and Policies: The route reflector can modify BGP attributes and apply routing policies as it reflects routes.

Key Considerations
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  • Design and Topology: Careful design is required to avoid routing loops and ensure redundancy, especially in networks with multiple route reflectors.
  • Cluster and Cluster ID: Route reflectors can be organized into clusters, each identified by a cluster ID to further enhance scalability and organization.

In summary, the route reflector is a critical concept in BGP used to enhance scalability and manageability of large networks by reducing the number of required iBGP sessions and simplifying the overall BGP configuration.