Load balancing and flow rules

This chapter provides an overview of how FortiGate-7000 Session-Aware Load Balancing (SLBC) works and then breaks down the details and explains why you might want to change some load balancing settings.

FortiGate-7000 SLBC works as follows.

1. SLBC attempts to match all incoming sessions with a configured flow rule (see Load balancing and flow rules). If a session matches a flow rule, the session is directed according to the action setting of the flow rule. Usually flow rules send traffic that can't be load balanced to a specific FPM.
2. TCP, UDP, SCTP, ICMP (IPv4 only) and ESP (IPv4 only) sessions that do not match a flow rule are directed to the DP2 processors.
   The DP2 processors distribute sessions to the FPMs according to the load balancing method set by the dp-load-distribution-method option of the config load-balance setting command.
   
3. All other sessions are sent to the primary FPM.