Technical Tip: How to load balance traffic between two interfaces via static routes

[nageentaj]

Description	This article discusses how to do ECMP load balancing with SDWAN configuration.
Scope	All Forti OS Models.
Solution	Using SD-WAN load balance of traffic can be done by navigating to SD-WAN -> SDWAN Rules ->Implicit Rule. There are 5 ways to load balance the traffic as shown below. The traffic will hit the implicit rule only when traffic doesn’t match any of the rules in the SD-WAN rules or if no rules are configured as shown below. In a scenario where there are SDWAN rules that are configured based on certain strategies example Manual, Best quality, Lowest cost (SLA), Maximum Bandwidth (SLA), these strategies help in selecting how the traffic will choose the outgoing interface but it can’t do load balancing as it does not match the implicit rule. In this case, create a static route for the same destination with the same administrative distance and priority as shown below, the traffic will match the longest prefix even though there is an SDWAN interface and load balancing will happen between the two interfaces PORT1 and PORT2. The routing table will look as shown below. Here if  '8.8.8.8' prefix length is 32 and one with default route ‘0’, so by default it will consider one with 32 prefix length. Find the active routes for the specific destination. References: https://docs.fortinet.com/document/fortigate/7.2.0/administration-guide/216765/implicit-rule https://docs.fortinet.com/document/fortigate/6.0.0/handbook/49719/configuring-sd-wan-load-balancing https://community.fortinet.com/t5/FortiGate/Technical-Tip-ECMP-Load-balancing-algorithms-for-IPv4-an...