L2TP and GRE are both tunneling protocols that can be used to create site-to-site VPNs. However, they have some differences in how they encapsulate and transport data. L2TP is a layer 2 protocol that uses IP packet encapsulation to carry PPP frames over an IP network. L2TP does not add any additional header to the IP packet, but relies on IPsec to provide encryption and authentication. GRE is a layer 3 protocol that adds its own header to the IP packet, which contains information such as the protocol type, checksum, and key. GRE can be used to carry any type of payload over an IP network, not just PPP frames. GRE also requires IPsec to provide security for the tunnel. Therefore, the correct answer is C, because GRE over IPsec adds its own header, and L2TP does not1234 References := 1: Implementing and Operating Cisco Security Core Technologies (SCOR) v1.0 - Module 5: Secure Connectivity 2: What is the difference between L2TP vs GRE 3: GRE over IPSec vs L2TP over IPSEC 4: difference between L2TP/GRE/MPLS