Technical Tip: Creating LAGs in FortiGate with multiple ISFs

Description

This article describes the recommended configuration for link aggregation to enable traffic offloading on FortiGates with multiple integrated switch fabrics (not all FortiGates have multiple ISFs). The goal is to avoid a specific corner case when attempting to stretch a link aggregation across two or more integrated switch fabrics.

Scope

FortiGate-3980E and all models with multiple integrated switch fabrics (ISF).

Solution

Creating a LAG using members from different ISFs is NOT supported and will cause issues with traffic offloading. To ensure proper functionality, avoid configuring LAG across multiple ISFs.

Related articles:
Viewing your FortiGate NP6, NP6XLite, or NP6Lite processor configuration
Increasing NP6 offloading capacity using link aggregation groups (LAGs)