fib_multipath_hash_policy

file: /proc/sys/net/ipv4/fib_multipath_hash_policy
variable: net.ipv4.fib_multipath_hash_policy
Official reference

Controls which hash policy to use for multipath routes. Only valid for kernels built with CONFIG_IP_ROUTE_MULTIPATH enabled. Default: 0 (Layer 3) Possible values: 0 - Layer 3 1 - Layer 4

source