What is Route Reflector?
A BGP router that redistributes iBGP learned routes to other iBGP peers, breaking the requirement for a full mesh of iBGP sessions.
A route reflector is a Border Gateway Protocol (BGP) router that relaxes the iBGP full-mesh rule. In standard iBGP, each router must peer with every other router in the same autonomous system (AS) to avoid routing loops. As the number of routers grows, this full mesh becomes impractical. A route reflector solves this by acting as a central hub. It accepts iBGP routes from its clients and reflects them to all other clients and non-client peers, while still applying the BGP path selection algorithm.
The route reflector uses three roles: client, non-client, and route reflector itself. Clients are iBGP speakers that peer only with the reflector. Non-clients are iBGP speakers that peer with the reflector but also maintain full mesh with other non-clients. The reflector propagates routes received from a client to all other clients and non-clients. Routes received from a non-client are sent only to clients. Routes received from an eBGP peer are sent to all clients and non-clients. To prevent loops, the reflector adds the originator ID and cluster list attributes. These attributes allow downstream routers to detect and discard routes that have already passed through the same cluster.
Route reflectors are widely deployed in large service provider and enterprise networks to scale iBGP. They are defined in RFC 4456, which obsoleted RFC 1966 and RFC 2796. A network can use multiple route reflectors for redundancy, often organized into clusters with a common cluster ID. Route reflectors do not modify the BGP next hop or AS path; they only change the route propagation rules. They are a fundamental tool for building scalable BGP networks without requiring a full iBGP mesh.
Key facts
- Eliminates the need for a full iBGP mesh by reflecting routes to clients.
- Defined in RFC 4456, which obsoleted RFC 1966 and RFC 2796.
- Uses originator ID and cluster list attributes to prevent routing loops.
- A route reflector can have multiple clients and multiple non-client peers.
- Multiple route reflectors can be deployed in the same AS for redundancy.
How it works in practice
Related terms
References
More in Networking & Routing
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