Using an RR helps reduce the number of MP-IBGP connections between PEs. The RR not only reduces the burden on PEs, but also facilitates network maintenance and management.
If too many PEs reside on the VPN backbone layer and these PEs need to establish MP-IBGP peer relationships to exchange VPN routes, you can configure route reflection to optimize the VPN backbone layer.
A BGP speaker does not advertise the routes learned from an IBGP peer to other IBGP peers. To enable a PE to advertise the routes of the VPN that the PE accesses to the BGP VPNv4 peers in the same AS, the PE must establish IBGP peer relationships with all peers to directly exchange VPN routing information. In other words, MP-IBGP peers must be fully meshed. If there are n PEs (including ASBRs) in an AS, n (n-1)/2 MP-IBGP peer relationships need to be established. A large number of IBGP peers consume a great number of network resources. After an RR is configured, each PE needs to set up an MP-IBGP peer relationship with only the RR, that is, only n pairs of MP-IBGP peers are required.