Per-Flow and Per-Prefix Load Balancing Overview
By default, when there are multiple equal-cost paths to the same destination, Junos OS chooses one of the next-hop addresses at random.
On all M Series Multiservice Edge Routers, MX Series 5G Universal Routing Platforms, and T Series Core Routers, you have the additional option of configuring per-prefix load balancing based on a specified hash value that enables the router to elect a next hop independently of the route chosen by other routers.
On the M120, M320, and MX Series routers only, you have the additional option of enabling per-flow load balancing based on a unique, load-balance hash value for each Packet Forwarding Engine slot.