Query

  • Can I configure two circuits with the same priority in SDWAN Forwarding Profile? If yes, what is the behavior?
  • How do the weighted round robin and high available bandwidth connection selection methods work?

Answer

You can configure up to eight circuits with the same priority in SDWAN Forwarding Profile, while up to eight priorities are supported. 


By default, Versa supports per flow load balancing. That is, packets for a given flow use the same path. Flows are load balanced across circuits/paths in the highest priority bucket that has SLA-compliant paths. The load balancing is weighted round robin, with the weights depending on the remaining capacity of the circuits.


In 16.1R2, we support the high-available-bandwidth connection selection method. Both weighted round robin as well as high available bandwidth are based on the remaining capacity on each SDWAN circuit. We periodically (every 3 seconds) measure the utilization and thereby calculate the remaining capacity of each circuit. The remaining capacity is with respect to the configured bandwidth of the local circuit (configured under interface bandwidth uplink/downlink). Each circuit is then given weights proportional to the remaining bandwidth.


Example #1

vni-0/1.0 (wan1) has a configured uplink and downlink bandwidth of 10M, and its utilization is 80% down, 20% up. vni-0/2.0 (wan2) has a configured uplink and downlink bandwidth of 5M, and its utilization is 75% down and up. The remaining capacity of wan1 is 2M down, 8M up, and its minimum available bandwidth is 2M. The remaining capacity of wan2 is 1M up and down, and so it has a minimum remaining capacity of 1M. For weighted round robin, the two circuits will now get weights in the ratio of 2M:1M. For a high available bandwidth, we select a circuit that has the highest available capacity (in this case, wan1). Note that we currently measure bandwidth only on physical ports. So any virtual interfaces used as wan interfaces (for example, a gre tunnel, or a vni subunit used as a cross connect to a redundant appliance) won't work.


Example #2

Let us consider two circuits C1 and C2, where:

  • C1 has 10 Mbps bandwidth, configured as part of interface configuration, and carries 58 flows that consume 8 Mbps.
  • C2 has 5 Mbps bandwidth, and carries 71 flows that consume 4 Mbps.

C1 has a remaining capacity of 2 Mbps, and C2 has remaining capacity of 1 Mbps. Now, C1 has twice the remaining capacity of C2. Therefore, C1 will get twice the load balancing weight than C2, and hence twice as many new traffic flows as C2. The remaining capacity is measured every few seconds to determine load balancing weights.


Per packet load balancing also follows weighted round robin logic.

For more information, refer the Versa SDWAN Traffic Steering Engine document.