Junos per packet load balancing

If you have two multiple equal cost paths to the same destination, JunOS behavior is to pick up one of the next-hops and use that one. For example in the following scenario, Junos keeps sending the packets via the ge-0/0/0.41 interface.

root@R4> show route 172.16.1.0

inet.0: 7 destinations, 7 routes (7 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

172.16.1.0/24      *[Static/5] 01:01:06
                    > to 10.30.41.31 via ge-0/0/0.41
                      to 10.30.40.30 via ge-0/0/0.40

but you can change this behavior ;

1) Write a policy statement

root@R4# show policy-options
policy-statement load_balance_per_packet {
    then {
        load-balance per-packet;
    }
}

2) Export this statement

[edit routing-options]
root@R4# show
forwarding-table {
    export load_balance_per_packet;
}

and here how it works;

root@R4> traceroute no-resolve 172.16.1.1
traceroute to 172.16.1.1 (172.16.1.1), 30 hops max, 40 byte packets
 1  10.30.41.31  3.825 ms 10.30.40.30  3.986 ms  3.997 ms
 2  10.20.30.2  3.992 ms  3.974 ms  4.001 ms
 3  172.16.1.1  5.963 ms  6.071 ms  3.974 ms

root@R4> traceroute no-resolve 172.16.1.1
traceroute to 172.16.1.1 (172.16.1.1), 30 hops max, 40 byte packets
 1  10.30.40.30  3.956 ms  3.986 ms 10.30.41.31  3.933 ms
 2  10.20.30.2  3.999 ms  4.073 ms  5.929 ms
 3  172.16.1.1  8.011 ms  7.949 ms  7.992 ms

I won’t lie it didn’t work this way when I tried this traceroute command first time. It worked actually but instead of 10.30.40.30 IP address on the first hop I was seeing 10.30.1.1 address which surprised me. Then I noticed that Junos is using the lowest IP address (10.30.1.1) on the configured interface as the source address and to change this behavior I type the following command on the other router ;

#set interfaces ge-0/0/1 unit 40 family inet address 10.30.40.30/24 primary

This command made this IP address primary because of which the expected output above displayed.