How does SD-WAN traffic steering work?

Updated 2/25/2019 11:41:56 AM by Comcast Expert


Traffic steering is a capability that sorts network traffic based on defined match conditions and steers as directed by the chosen traffic steering behavior. Traffic steering is only available if the user has two or more used WAN or hybrid WAN ports (when SD-WAN is paired with private IP networks, for example, IP-VPN, MPLS, Ethernet networks). The default setting for traffic steering is to steer outbound traffic based on the numerical rank of WAN and hybrid WAN links, which is set during the initial network setup. Once traffic steering rules are applied, these rules override the default settings.

Traffic steering rules are only applied to VPN traffic on egress. Internet traffic currently cannot be processed by the traffic steering engine, but there is one exception to this rule. If using centralized internet breakout, then the internet-bound traffic traveling through the VPN to a centralized site is capable of being steered, since this internet traffic is inside the VPN tunnel.

Below is a reference guide to traffic match options and behavior options for traffic steering rules:

Traffic Match Options
Known applications
Application family
IP prefix source
IP prefix destination
VPN Name
Behavior Options
By lowest latency
Manually choosing a link
By MOS score
Manually choosing links to exclude
Manually choosing links to replicate
Manually choosing links to load balance


Traffic steering rules have the following structure:

  • Traffic Steering Profile: A collection of traffic steering rules.
  • Traffic Steering Rule: Contains one or many traffic signatures and the selected steering behavior.
  • Traffic Signature: Contains one or many match conditions.
  • Match conditions: Specifies the attributes of the network traffic that are being targeted for traffic steering. 

The traffic steering tile will only appear on the Site Services screen when there are two or more WAN links setup at a given site.

After advancing to the traffic steering management page, the user can view the current profile of traffic steering rules. If rules already exist, the user can manage the priority level of them. If the user would like to add a new rule, they should click on the corresponding link. 

When adding a new rule, the user will have to establish a unique name for this traffic steering rule.

Once a rule name is established, the user designates a traffic signature for this rule. The user can create a new traffic signature, or choose one that has been made previously in other traffic steering rules. For simplicity, let’s assume the user chooses an existing traffic signature, for example, FTP. Under the established traffic signature, the user must assign match conditions that specify further which types of network traffic will be sorted with this rule. For a created traffic signature, the user chooses match conditions associated with it. For existing signatures, there are predefined match conditions. In this example, the match condition associated with FTP is Applications.

After determining the traffic signature and the steering conditions, the user can select between six behaviors to dictate where the traffic is sent: by lowest latency, manually choosing a link, by MOS score, or by manually choosings link(s) to exclude, replicate or load balance. Directing traffic by lowest latency is self-explanatory and doesn’t require any additional specifications once selected. 

Manually choosing a link requires the user to choose a port number for traffic direction.

Directing traffic by MOS score can either be conducted by the default 3.5 score or by a new value designated by the user.

Manually choosing links to exclude requires the user to choose at least one port that will not be sent traffic.

Manually choosing links to replicate requires the user to choose at least two ports.

Manually choosing links to load balance requires the user to select at least two ports.

After finalizing the behavior of the rule, the rule is ready to be implemented. Once it is created, the user can revise the priority levels of the traffic steering.

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