SD-WAN rules - best quality

SD-WAN rules are used to control how sessions are distributed to SD-WAN members. Rules can be configured in one of five modes:

• auto: Interfaces are assigned a priority based on quality.
• Manual (manual): Interfaces are manually assigned a priority.
• Best Quality (priority): Interface are assigned a priority based on the link-cost-factor of the interface.
• Lowest Cost (SLA) (sla): Interfaces are assigned a priority based on selected SLA settings. See SD-WAN rules - lowest cost (SLA).
• Maximize Bandwith (SLA) (load-balance): Traffic is distributed among all available links based on the selected load balancing algorithm. See SD-WAN rules - maximize bandwidth (SLA).

When using Best Quality mode, SD-WAN will choose the best link to forward traffic by comparing the link-cost-factor, selected from one of the following:

GUI	CLI	Description
Latency	latency	Select a link based on latency.
Jitter	jitter	Select a link based on jitter.
Packet Loss	packet-loss	Select a link based on packet loss.
Downstream	inbandwidth	Select a link based on available bandwidth of incoming traffic.
Upstream	outbandwidth	Select a link based on available bandwidth of outgoing traffic.
Bandwidth	bibandwidth	Select a link based on available bandwidth of bidirectional traffic.
custom-profile-1	custom-profile-1	Select link based on customized profile. If selected, set the following weights: packet-loss-weight: Coefficient of packet-loss. latency-weight: Coefficient of latency. jitter-weight: Coefficient of jitter. bandwidth-weight: Coefficient of reciprocal of available bidirectional bandwidth.

In this example, your wan1 and wan2 SD-WAN interfaces connect to two ISPs that both go to the public internet, and you want Gmail services to use the link with the least latency.

To configure an SD-WAN rule to use Best Quality:

1. On the FortiGate, enable SD-WAN and add wan1 and wan2 as SD-WAN members, then add a policy and static route. See Creating the SD-WAN interface for details.
2. Create a new Performance SLA named google. See Performance SLA - link monitoring.
3. Go to Network > SD-WAN Rules.
4. Click Create New. The Priority Rule page opens.
5. Enter a name for the rule, such as gmail.
6. Configure the following settings:

   

   Field	Setting
   Internet Service	Google-Gmail
   Strategy	Best Quality
   Interface preference	wan1 and wan2
   Measured SLA	google (created in step 2).
   Quality criteria	Latency

7. Click OK to create the rule.

To configure an SD-WAN rule to use priority:

config system virtual-wan-link
    config health-check
        edit "google"
            set server "google.com"
            set members 1 2
        next
    end
    config service
        edit 1
            set name "gmail"
            set mode priority
            set internet-service enable
            set internet-service-id 65646
            set health-check "google"
            set link-cost-factor latency
            set priority-members 1 2
        next
    end
end

To diagnose the Performance SLA status:

FGT # diagnose sys virtual-wan-link health-check google
Health Check(google):
Seq(1): state(alive), packet-loss(0.000%) latency(14.563), jitter(4.334) sla_map=0x0
Seq(2): state(alive), packet-loss(0.000%) latency(12.633), jitter(6.265) sla_map=0x0

FGT # diagnose sys virtual-wan-link service 1

Service(1):

    TOS(0x0/0x0), protocol(0: 1->65535), Mode(priority), link-cost-facotr(latency), link-cost-threshold(10), health-check(google) Members:

        1: Seq_num(2), alive, latency: 12.633, selected
        2: Seq_num(1), alive, latency: 14.563, selected

    Internet Service: Google-Gmail(65646)

As wan2 has a smaller latency, SD-WAN will put Seq_num(2) on top of Seq_num(1) and wan2 will be used to forward Gmail traffic.