CCNA Practice Exam 2026 – Complete Study Resource

When configuring a Generic Routing Encapsulation (GRE) tunnel, it is essential to specify the tunnel source and destination. The correct requirement is that the tunnel source must be a public Internet IP address. This is because GRE tunnels are often used to encapsulate packets in scenarios where the routers are located on different networks, potentially spread over the Internet. In these situations, using a public IP address as the tunnel source ensures that the encapsulated packets can traverse the Internet and reach the destination router.

The tunnel destination is typically an IP address that the source router can reach via its routing table, which is often a public IP address of the remote router in GRE configurations. Thus, establishing a connection between two routers across the public Internet is most effective when the source is a public IP.

Other alternatives do not accurately reflect the requirements for GRE tunneling. For instance, both routers are not required to have the same tunnel interface number as they operate independently. The tunnel destination does not need to be a private IP address; it can be a public one that is reachable. Lastly, there is no requirement for both devices to run the same routing protocol for GRE to function correctly; GRE operates at a Layer 3 level, independent of the routing protocol used.