NSR for BGP RPKI

This feature introduces nonstop active routing (NSR) support for BGP Origin Validation using resource public key infrastructure (RPKI). The NSR model for routing protocols is based on replicating the routing states between primary and backup Routing Engines, so that the backup Routing Engine has the same information and configuration as the primary Routing Engine. Therefore, when NSR is enabled, the route validation (RV) database entries are replicated between the primary and backup Routing Engines. Although RV record state is replicated, the NSR for RPKI doesn't replicate RV session state. Upon NSR switchover, the RV sessions are recovered using the procedures similar to BGP graceful restart, where the RV session(s) to the RPKI caches will drop and get reestablished. There is no need to keep the RV session up because the RPKI cache information is valid until the RV record's lifetime expires, regardless of the RV session state. Following NSR switchover, the newly promoted primary Routing Engine connects to its RPKI caches and reconciles all RV records that it has obtained while being the backup.