The correct answer is GRE because it is designed to encapsulate a wide range of network layer protocols for transmission over an IP network, which is ideal for transmitting non-IP traffic. Unlike GRE, IPsec is primarily focused on secure IP traffic and does not inherently support the encapsulation of non-IP protocols. SSL/TLS generally secures application layer data for things like web traffic and does not operate at the network layer to encapsulate network layer protocols. L2TP does encapsulate traffic, but primarily for creating VPNs, it also tends to encapsulate PPP traffic over IP networks and does not have the same flexibility as GRE for multiple protocols.