Cisco Certified Network Associate (CCNA) Practice Exam

What protocol allows devices to communicate with each other when they are on different network layer protocols?

1. 6to4 tunneling

2. GRE tunneling

3. ISATAP tunneling

4. Teredo tunneling

The correct answer is: GRE tunneling

The correct option is GRE tunneling, which stands for Generic Routing Encapsulation. This protocol is designed to encapsulate a wide variety of network layer protocols, allowing them to be transmitted over a network that may be using a different protocol, such as IPv4 encapsulating IPv6 or vice versa. GRE tunnels can carry any network layer protocol across an IP network, making it a versatile solution for communicating across different network layer protocols. While options like 6to4, ISATAP, and Teredo are also tunneling protocols, they are specifically tailored for IPv6 and have limitations on the types of packets they can encapsulate or the scenarios in which they are best utilized. 6to4 and Teredo, for instance, are primarily solutions for IPv6 traffic transmitting over an IPv4 network. ISATAP serves similar purposes by allowing IPv6 packets to be transmitted over IPv4 networks, but it has specific use cases within IPv6 transition strategies. Thus, GRE is more broad and adaptable compared to the other options, allowing communication across multiple protocol types beyond just IPv4 and IPv6, which is why it stands out as the preferred choice for a protocol that facilitates communication among devices using different network layer protocols.