The SLA compliance state of all paths for a forwarding profile is re-evaluated after every recompute interval. If a path (for example, WAN1) is non-compliant, all traffic flows that are currently using the said path, are migrated to a different SLA compliant path if available (for example, WAN2). However, if the SLA violation is caused by the traffic load, WAN1 may now become SLA compliant, and WAN2 will become non-compliant. After one recompute interval, all flows will migrate back to WAN1. This oscillation may be prevented using gradual migration.

When gradual migration is enabled, flows are moved off non compliant paths over a few re-computation cycles, instead of all at once. This eases the load on WAN1, bringing it back into compliance. Flows diverted to WAN2 stay there as long as it remains SLA compliant, and does not attempt to switch back. Flows that did not divert to WAN2 may be able to stay on WAN1, since load reduction on WAN1 brings it back into compliance.

Gradual migration is disabled by default. Note that for gradual migration to work, continuous evaluation must be enabled in Versa Director.