Per-Flow and Per-Prefix Load Balancing Overview

By default, when there are multiple equal-cost paths to the same destination, the JUNOS Software chooses one of the next-hop addresses at random.

On all M Series Multiservice Edge Routers, MX Series Ethernet Services Routers, and T Series Core Routers, you have two additional options:

• You can specify what information the routing platform uses for per-flow load balancing based on port data (instead of on source and destination IP addresses only). For aggregated Ethernet and aggregated SONET/SDH interfaces, you can load-balance based on the MPLS label information. For more information, see Configuring Per-Packet Load Balancing.
• You can also configure per-prefix load balancing, which allows you to configure a hash value that enables the router to elect a next hop independently of the route chosen by other routers. For more information, see Configuring Per-Prefix Load Balancing.

In addition, on the M120, M320, and MX Series routers only, you have the following option:

• You can also configure per-flow load balancing, which allows you to configure the router to assign a unique, load-balance hash value for each Packet Forwarding Engine slot. For more information, see Configuring Per-Flow Load Balancing Based on Hash Values.