On Cisco vEdge devices and Cisco IOS XE SD-WAN devices, each interface has eight queues, which are numbered 0 to 7. Queue 0 is reserved, and is used for both control traffic and low- latency queuing (LLQ) traffic. For LLQ, any class that is mapped to queue 0 must also be configured to use LLQ. Queues 1 to 7 are available for data traffic, and the default scheduling for these seven queues is weighted round-robin (WRR). For these queues, you can define the weighting according to the needs of your network. When QoS is not configured for data traffic, queue 2 is the default queue.
https://www.cisco.com/c/en/us/td/docs/routers/sdwan/configuration/qos/vEdge-20-x/qos- book/forwarding-qos.html