NetworkPuzzles

Quality of Service (QoS) is a fundamental requirement in enterprise networks, especially when different types of traffic—such as voice, video, and bulk data—share the same WAN links.

Cisco SD-WAN provides a structured QoS model that allows traffic to be:

• classified
• marked
• queued
• scheduled
• and controlled under congestion

In this post, I’ll explain how QoS works in Cisco SD-WAN, how it differs from traditional Cisco QoS (MQC), and how traffic is handled from classification to hardware queue scheduling.

Traditional Cisco QoS (MQC)

• Class-Map → classify traffic
• Policy-Map → define actions
• Service-Policy → apply to interface

Cisco SD-WAN QoS Model

Instead of MQC, SD-WAN uses:

• Forwarding Classes
• Hardware Queues
• Schedulers
• QoS Map
• Applied directly to WAN interfaces

SD-WAN QoS Flow

Traffic → Forwarding Class → Hardware Queue → Scheduler → QoS Map → Interface

Step-by-Step QoS in Cisco SD-WAN

Step 1: Assign Traffic to Forwarding Classes

Traffic is first classified into Forwarding Classes.

Examples:

• Voice
• Video
• Critical Data
• Bulk
• Default

We can map based on:

• DSCP
• application
• ACL
• or policy

Step 2 — Map Forwarding Classes to Hardware Queues

Cisco SD-WAN uses 8 hardware queues (0–7).

Example:

Step 3 — Configure Queue Behavior

Each queue can be configured with:

• bandwidth-percent
• buffer-percent
• scheduling method
• drop behavior

Scheduling Types

• LLQ (Low Latency Queue) → strict priority
• WRR (Weighted Round Robin) → fair sharing

Example:

• Voice → LLQ (priority queue)
• Other traffic → WRR

Step 4 — Create QoS Map

A QoS Map combines:

• forwarding classes
• queue assignments
• scheduling behavior

This is similar to a policy-map in MQC.

policy
  qos-scheduler QoS-map1_0
   class Queue0
   bandwidth-percent 30
   buffer-percent 30
   scheduling llq
   drops tail-drop
   burst 15000
  !
  qos-scheduler QoS-map1_1
   class Queue1
   bandwidth-percent 40
   buffer-percent 40
   scheduling wrr
   drops red-drop
  !
  qos-scheduler QoS-map1_2
   class Queue2
   bandwidth-percent 30
   buffer-percent 30
   scheduling wrr
   drops red-drop
  !
  qos-map QoS-map1
   qos-scheduler QoS-map1_0 
   qos-scheduler QoS-map1_1 
   qos-scheduler QoS-map1_2 
  !
  class-map 
   class Bulk queue 1 
   class Other queue 2 
   class Queue0 queue 0 
   class Queue1 queue 1 
   class Queue2 queue 2 
  !
 cloud-qos 
 cloud-qos-service-side 
!

We should add the Policy to the edge device Template, after that we can use it on the interface:

  policy
		   cloud-qos
		   cloud-qos-service-side
		   class-map
		    class Bulk queue 1
		    class Other queue 2
	       class Queue0 queue 0
		    class Queue1 queue 1
		    class Queue2 queue 2
		   !
		   qos-scheduler QoS-map1_0
	        class             Queue0
		    bandwidth-percent 30
		    buffer-percent    30
		    scheduling        llq
		    drops             tail-drop
		    burst             15000
		   !
		   qos-scheduler QoS-map1_1
		    class             Queue1
		    bandwidth-percent 40
		    buffer-percent    40
		    scheduling        wrr
		    drops             red-drop
		   !
		   qos-scheduler QoS-map1_2
		    class             Queue2
		    bandwidth-percent 30
		    buffer-percent    30
		    scheduling        wrr
		    drops             red-drop
		   !
		   qos-map QoS-map1
		    qos-scheduler QoS-map1_0
		    qos-scheduler QoS-map1_1
		    qos-scheduler QoS-map1_2
		   !

Step 5 — Apply QoS Map to Interface

QoS Map → WAN Interface

vpn 1
  interface ge0/1
    ip address 10.10.24.1/24
    no shutdown
   qos-map  QoS-map1

Example Traffic Policy

QoS only becomes important when the link is congested.