Technical Tip: How to configure LLB with the purpose of balancing the connection through the multiple outgoing interfaces (or ISP links)

[JordAnge]

Description	This article describes how to configure LLB with the purpose of balancing the connection through the multiple outgoing interfaces (or ISP links). The FortiADC balances traffic among multiple upstream links. If the primary link fails., traffic is seamlessly redirected through a backup link. It is possible to configure link load balancing for inbound traffic, outbound traffic, or both. Outbound link load balance is the most used configuration. Many of the optional objects are configured as system-wide shared resources. Examples of optional objects include schedule, address, service, and health check.
Scope	FortiADC. There is no need to have 2 or more ISPs to configure link-load-balance. It can be configured with just 1 ISP and monitor the bandwidth usage of it. Topology:                                                 ISP-1 LAN         ===> FADC ===|                                                 ISP-2
Solution	Configure the network interfaces associated with the upstream links. From Link Group -> Gateway, configure the gateway-address associated with the upstream interfaces. Optionally it is possible to set a health-check to monitor the availability of the gateway and to set the Inbound/Outbound bandwidth (Kbps) as well as the Spillover based on the bandwidth in upstream links. From Link Group -> Link Group, set the name and the gateways previously configured. Set the Route Method and persistence used to balance the connections between the upstream links. On Link Members, it is possible to set the gateways, the weight, and the role (primary/backup) of them. Go to Link Policy, create a new policy, and configure the Ingress Interface and the Link Group that includes the upstream links. The policy can be applied based on: Source. Destination. Service. Schedule. From FortiView -> LINK LOAD BALANCE -> Gateway, it will be visible the gateways configured. Enable the 'Monitor' checkbox to display the throughput (Inbound / Outbound) of the ISP link. From Log & Report -> Traffic Log can be visible the balance of connections. LLB checkbox must be enabled first from Log & Report -> Log Setting.