Discussion

Solution
Create a routing policy that load-balances traffic on a per-flow basis:
[edit policy-options]
aviva@router1# set policy-statement balance-traffic from route-filter 192.168.10.0/24
orlonger
aviva@router1# set policy-statement balance-traffic then load-balance per-packet
Then apply the policy to the forwarding table:
[edit routing-options]
aviva@router1# set forwarding-table export balance-traffic
Discussion
The routing protocols populate the routing table with the routes they know about
and learn from their neighbors. For each prefix, or destination, RPD chooses one
active route and installs its next hop into the forwarding table. If a route points to an
indirect next hop, RPD downloads all the next hops of the indirect next hop, and the
PFE selects a single next hop to use.
When there are multiple paths to a single destination, the routing protocols install
the next hops for each path into the routing table. The protocols do have some
degree of freedom when populating the routing table. A protocol can opt to install
multiple routes, each with the same next hop, a single route with multiple next hops,
or even multiple routes with multiple next hops. BGP, for example, can use any of
these variations depending on how many peers advertise a prefix, how those peers
can be reached, and whether BGP multipath is enabled.
When an active route has multiple equal-cost paths, the default behavior is for RPD
to use a hash algorithm to choose a single gateway and install it into the forwarding
table. If multiple prefixes have a common set of next hops, this gateway selection
process should result in uniform distribution of prefixes across the next hops. For
example, if prefixes A, B, C, and D all have gateways 1 and 2, RPD may install A and
D with gateway 1 and Band C with gateway 2, so half the prefixes go through one
link and half through the other.
To instead have RPD install all the next hops for a prefix into the forwarding table,
you turn on load balancing for that prefix. Load balancing distributes the traffic to
the prefix across all the paths, evening out the traffic flow across different interfaces
and circuits.
Configuring load balancing is a two-step process. First, create a routing policy to
define which packets to load-balance. In this recipe, the from clause matches the prefix
192.168.10.0/24 and any longer prefixes. The then clause has the load-balance
per-packet action to turn on load balancing:
[edit policy-options]
aviva@router1# set policy-statement load-balance then load-balance per-packet
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Load-Balancing Traffic Flows | 271