Persistent Route Oscillation in BGP Constrained Route Distribution

RFC4684 defines Multi-Protocol BGP (MP-BGP) procedures that allow BGP speakers to exchange Route Target reachability information (RT- Constrain) to restrict the propagation of Virtual Private Network (VPN) routes. In network scenarios where hierarchical route reflection (RR) is used, the existing RT-Constrain mechanism may result in persistent route oscillations within RRs. This document describes the problem and proposes a solution.