Next-hop tracking

In SR OS next-hop resolution is not a one-time event. If the IP route or tunnel that was used to resolve a BGP next-hop is withdrawn because of a failure or configuration change an attempt is made to re-resolve the BGP next-hop using the next-best route or tunnel. If there are no more eligible routes or tunnels to resolve the BGP next-hop then the BGP next-hop becomes unresolved. The continual process of monitoring and reacting to resolving route/tunnel changes is called next-hop tracking. In SR OS next-hop tracking is completely event driven as opposed to timer driven; this provides the best possible convergence performance.