Cisco Catalyst SD-WAN Forwarding and QoS Overview
Forwarding takes the data packet and sends it over the transport to the remote side, specifying what to do with the packet. It specifies the interface through which packets are sent to reach the service side of a remote router.
Once the control plane connections of the Cisco Catalyst SD-WAN overlay network are up and running, data traffic flows automatically over the IPsec connections between the routers. Because data traffic never goes to or through the centralized Cisco SD-WAN Controller, forwarding only occurs between the Cisco IOS XE Catalyst SD-WAN devices as they send and receive data traffic.
While the routing protocols running in the control plane provide a router the best route to reach the network that is on the service side of a remote router, there will be situations where it is beneficial to select more specific routes. Using forwarding, there are ways you can affect the flow of data traffic. Forwarding takes the data packet and sends it over the transport to the remote side, specifying what to do with the packet. It specifies the interface through which packets are sent to reach the service side of a remote router.
To modify the default data packet forwarding flow, you create and apply a centralized data policy or a localized data policy. With a centralized data policy, you can manage the paths along which traffic is routed through the network, and you can permit or block traffic based on the address, port, and DSCP fields in the packet's IP header. With a localized data policy, you can control the flow of data traffic into and out of the interfaces of a router, enabling features such as quality of service (QoS).