Appendix A: SD-WAN Processing Application Flows (Informative)

There are several steps in determining how to forward ingress IP Packets as shown in Figure 6.¹¹

Figure 6 – Application Flows and Policies

After an IP Packet enters the SD-WAN Edge at the Ingress UNI, it is inspected to identify with which Application Flow it is associated (if the packet does not match any of the defined Application Flows, it is discarded). Then, a Policy is applied to the packet which, in conjunction with the properties of the TVCs, results in a list of TVCs that can carry the IP Packet (in the diagram, TVC1 and TVC2). If no Policy has been assigned to the Application Flow at this End Point, it is discarded. The IP Forwarder determines which TVCs can reach the destination (in the diagram, TVC2 and TVC4). The intersection of these results yields the TVC (or TVCs) that can carry the IP Packet (in this case, TVC2). Of course, it is possible for the intersection to include more than one TVC, in which case the Service Provider can choose any of them—the choice could be based on load balancing, performance optimization, or other criteria.

If the Ingress IP Packet is part of an Application Flow whose Policy indicates that Internet Breakout is required, the packet will likely follow the Local Internet Breakout path shown in the diagram since UCS #1 is an Internet service.

This is a conceptual representation of the SD-WAN Edge functionality. The Policy process and IP For-warder are shown in parallel. In a given implementation they could run in parallel (as shown) or they could be sequential in either order. The description is implicitly assuming forwarding based on standard IP rout-ing, but other IP forwarding approaches are possible, such as Policy-Based Routing, in which case this part of the process might be included in the “Apply Policy” process. The details of the implementation are beyond the scope of this document. The relevant point is that an IP Packet arrives, and it is either discarded or assigned to a TVC based on the Policy and IP Forwarding requirements of the IP Packet.

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¹¹ This example assumes that the Service Provider has created all of the necessary TVCs to meet the Policy and connectivity requirements of the SD-WAN Service, and that the necessary IP routing information has been agreed to and configured.