Route Target Constraint (RTC) uses the rtfilter address family. In a normal Multiprotocol Label Switching (MPLS) virtual private network (VPN), the route reflector (RR) sends all of its VPN version 4 (VPNv4) and VPNv6 prefixes to the Provider Edge (PE) router. The PE router then drops the prefixes for which it does not have a matching VPN routing and forwarding (VRF). RTC sends only prefixes that the PE router wants. When RTC is enabled, the PE router sends its route target (RT) membership data to the RR within an address family named rtfilter. The RR then uses rtfilter to determine which prefixes to send to the PE. In order for RTC to work, both the RR and the PE need to support RTC.
Border Gateway Protocol (BGP) Enhanced Route Refresh finds route inconsistencies, and if inconsistencies exist, peers are synchronized without a hard reset. If two BGP peers support Enhanced Route Refresh, each peer will send a RouteRefresh StartofRIB (SOR) message and a RouteRefresh EndofRIB (EOR) message before and after an AdjRIBOut message, respectively. After a peer receives an EOR message, or after the EOR timer expires, the peer will check to see whether it has any routes that were not readvertised. If any stale routes remain, they are deleted and the route inconsistency is logged.
Unified Multiprotocol Label Switching (MPLS) makes the area border router (ABR) an RR and sets the next hop to self. Unified MPLS increases scalability for an MPLS network by extending the label switched path (LSP) from end to end, not by redistributing interior gateway protocols (IGPs) into one another, but by distributing some of the IGP prefixes into BGP. BGP then distributes those prefixes throughout the network.
BGP Prefix Independent Convergence (PIC) improves convergence by creating and storing an alternate path in the Routing Information Base (RIB), Forwarding Information Base (FIB), and Cisco Express Forwarding (CEF). As soon as a failure is detected, BGP uses the alternate path. BGP PIC works on IPv4, IPv6, and MPLS networks.