https://en.wikipedia.org/wiki/Equal-cost_multi-path_routing
Equal-cost multi-path routing (ECMP) is arouting strategy wherenext-hop packet forwarding to a single destination can occur over multiple "best paths" which tie for top place in routing metric calculations. Multi-path routing can be used in conjunction with most routing protocols, because it is a per-hop decision limited to a single router. It can substantially increase bandwidth by load-balancing traffic over multiple paths; however, there may be significant problems in deploying it in practice.[1]RFC 2991 discusses multi-path routing in general.
In 2014, the Institute of Electrical and Electronics Engineers (IEEE) incorporated Equal Cost Multiple Paths (ECMP) or IEEE standard 802.1Qbp intoIEEE 802.1Q-2014 for Shortest Path Bridging. Specifying the forward and reverse paths used for unicast andmulticast traffic in shortest path bridging as symmetric insuring flows on deterministic paths, resolving configuration complexities, management functionality and performance issues within original standards implementations.[2][3][4][5][6]