In a typical production SD-WAN deployment, it is common for WAN edge routers to have multiple SD-WAN policy types applied. In such scenarios, we should know the order of operations of an Edge router and how the policies interact with each other.
Figure 9.26 above illustrates the order in which a WAN edge router executes each policy type.
- When a WAN edge router receives data traffic on one of its LAN interfaces, it matches the packets against the applied Local Ingress Policy, which, in a sense, is just an access list (ACL) applied inbound on the LAN interface. If the traffic flow is not dropped, the WAN edge router passes it for evaluation to the applied Application-aware Routing Policy.
- The router matches the traffic against the applied application-aware routing policy. If the traffic flow is not dropped by a strict action, it passes it to the data policy for evaluation.
- The router then matches the traffic against the applied centralized data policy.