BGP multipath allows load sharing among multiple EBGP paths and multiple IBGP paths of IPv4 routes. A path is considered a BGP equal-cost path (and will be used for forwarding) if a tie-break is needed. The tie-break is performed after the BGP route path selection step that chooses the next-hop path that is resolved through the IGP route with the lowest metric, allowing traffic load balancing across multiple BGP next hops resolved through the IGP routes with equal metric.
All paths with the same neighboring autonomous system, learned by a multipath-enabled BGP neighbor, are considered. If IGP routes, through which BGP next hops are resolved, are equal, but in some preceding step in the BGP path selection process (for example, MED comparison) the best path is selected, BGP multipath does not come into effect, and traffic is sent only toward the selected BGP path.
