Description | This article describes the behavior modification of how FortiOS determines the SD-WAN member order when using the Lowest Cost (SLA) Algorithm. |
Scope |
FortiGate v6.4.10 and v 7.0.9 and later. |
Solution |
The scenario is as explained below:
Spoke will establish an IPSec tunnel to both hubs on both ISP links, so Spoke will have 4 IPSec tunnels. There are HUB1-ISP1, HUB1-ISP1, HUB2-ISP1, HUB2-ISP2.
2 Performances SLA created on Spoke to the server behind each HUB:
Spoke # dia sys sdwan health-check
The expected order of SD-WAN members is:
1. HUB1-ISP1 2. HUB2-ISP1 3. HUB1-ISP2 4. HUB2-ISP2
When both SLA targets are met, the order of the outgoing interface will follow the order of interface preference:
Spoke # dia sys sdwan service Service(1): Address Mode(IPV4) flags=0x200 Dst address(1):
This is the behavior on version 6.4.10.
On version 7.0.9, the default order is changed. How to assign the SLA Target is also considered. With the same configuration, this is the order:
Spoke # dia sys sdwan service Service(1): Address Mode(IPV4) flags=0x200 use-shortcut-sla Dst address(1):
If HUB2 SLA Target first is put, then the order will change:
Spoke # dia sys sdwan service Service(1): Address Mode(IPV4) flags=0x200 use-shortcut-sla Dst address(1):
To make sure that the order of the outgoing interface follows the order of interface preference on SD-WAN rules, it is necessary to change the 'sla-compare-method' option, from 'order' to 'number':
config system sdwan config service edit 1 set sla-compare-method order <----- Compare SLA value based on the order of health-check. number <----- Compare SLA value based on the number of satisfied health-check. |
The Fortinet Security Fabric brings together the concepts of convergence and consolidation to provide comprehensive cybersecurity protection for all users, devices, and applications and across all network edges.
Copyright 2025 Fortinet, Inc. All Rights Reserved.