Release 5.1, Revision 0 Copyright © 2001, Juniper Networks, Inc. Advanced Juniper Networks Routing Module 7: BGP Route Reflection

Copyright © 2001, Juniper Networks, Inc. Objectives Describe the operation of BGP route reflection Configure a route reflector Explain the flow of routing information in a route reflection network

Copyright © 2001, Juniper Networks, Inc. Scaling BGP IBGP full-mesh peer requirement has an N-squared problem – Addition of a new router requires new peering with all current IBGP speakers – Current IBGP speakers must update configurations Route Reflection (RFC 2796) is one method for scaling IBGP connectivity

Copyright © 2001, Juniper Networks, Inc. Route Reflection Concepts Allows an IBGP speaker to re-advertise an IBGP learned route to another IBGP speaker Route Reflector (RR) only re-advertises the best route to “clients” IBGP attributes are not changed by reflection Routing Loops are prevented by new BGP attributes of Cluster-id, Cluster-list, and Originator-id

Copyright © 2001, Juniper Networks, Inc. Route Reflection Attributes Cluster-id represents each RR cluster in the network – RR will drop routes that have already transited the cluster – Added to the cluster-list when the RR advertises outside of the cluster Cluster-list operates like an AS_Path – RR use it for loop prevention – Routers can use it in the route selection algorithm Originator-id denotes the first router to inject a route in a RR network

Copyright © 2001, Juniper Networks, Inc. Route Reflection Configuration Route reflector clients are configured in a separate peer group Each peer group uses the cluster keyword – Unique 32-bit number if used as the cluster-id – Often the router-id of the RR is used Clients only peer to their route reflectors [edit protocols bgp] group int-peers { type internal; local-address ; cluster ; neighbor ; neighbor ; neighbor ; } [edit protocols bgp] group int-peers { type internal; local-address ; neighbor ; }

Copyright © 2001, Juniper Networks, Inc. RR Client Full Mesh Clients may also peer with each other member of the RR cluster To stop unnecessary advertisements, configure the RR with the no-client-reflect command [edit protocols bgp] show group int-peers { type internal; local-address ; neighbor ; neighbor ; } [edit protocols bgp] show group int-peers { type internal; local-address ; neighbor ; neighbor ; } [edit protocols bgp] show group int-peers { type internal; local-address ; cluster ; no-client-reflect; neighbor ; neighbor ; }

Copyright © 2001, Juniper Networks, Inc. “Basic” Route Reflection Client –> RR –> clients & non-clients Non-client –> RR –> clients only

Copyright © 2001, Juniper Networks, Inc. Hierarchical Route Reflection Client –> RR –> clients & non-clients Non-client –> RR –> clients only

Copyright © 2001, Juniper Networks, Inc. Route Propagation (1 of 3) Routes are sent from a client to all peers (route reflector) /24

Copyright © 2001, Juniper Networks, Inc. Route Propagation (2 of 3) Route reflector sends routes to all clients in the cluster and all peers / / /24

Copyright © 2001, Juniper Networks, Inc. Route Propagation (3 of 3) Route reflector sends routes from peers to all clients in the cluster / /24

Copyright © 2001, Juniper Networks, Inc. Review Questions What does a BGP route reflector do with BGP routes received from a configured RR client router? What three BGP attributes are introduced when BGP route reflection is used and what is their role?