RouteReflectors

Route Reflectors are a BGP mechanism used to scale iBGP in large networks. In a traditional iBGP mesh, every router must maintain a session with every other iBGP peer, which becomes impractical as the network grows. A route reflector design designates one or more routers as route reflectors and configures other routers as route reflector clients. The reflector learns routes from its clients (and from other reflectors) and reflects those routes to its clients, reducing the number of iBGP sessions needed while preserving route information and policy.

Key concepts include the route reflector itself, its clients, and the cluster concept. A cluster represents a group of routers that share a common reflector and are identified by a cluster ID. The cluster-list attribute is used in BGP updates to prevent reflection loops, ensuring the same route is not reflected back and forth within a cluster. Route reflection allows routes learned from a client to be advertised to other clients, and it can propagate routes learned from non-clients or other reflectors as configured.

Route Reflectors are widely used in service provider networks, large data centers, and enterprises to scale iBGP, often deployed in hub-and-spoke or multi-reflector topologies. Redundancy is typically addressed by deploying multiple reflectors or reflector clusters, sometimes in conjunction with confederations to further reduce iBGP scaling.

Limitations and considerations include potential suboptimal routing if a reflector path is not the best available, and the risk of a single point of failure if reflector redundancy is not implemented. Proper design, policy consistency, and monitoring are important to realize the benefits of route reflection without compromising routing quality. Configuration usually involves designating neighbors as route-reflector-clients and assigning a stable cluster ID on the reflector devices.