In Cisco SD-WAN, the VPN (Virtual Private Network) identifier is carried in the data packet using a specific field called the VPN ID field. The VPN ID field is a part of the SD-WAN encapsulation header, which is added to the original packet to facilitate routing and forwarding within the SD-WAN infrastructure.
The VPN ID field contains the identifier or label that represents the specific VPN instance to which the data packet belongs. It helps the SD-WAN devices (routers, gateways, etc.) in the network to determine the appropriate path and treatment for the packet based on the configured VPN policies.
The exact format and location of the VPN ID field in the SD-WAN data packet may vary depending on the specific implementation and protocol being used. However, in general, it is a dedicated field within the encapsulation header that carries the VPN identifier information for proper routing and handling within the SD-WAN network.