It should also be noted the connection type used is '''Tunnel''' and not '''Transport'''. Tunnel protects the internal routing information by encrypting the IP header of the original packet. The original packet is encapsulated by a another set of IP headers. Transport encrypts only the payload and Encapsulating Security Payload (ESP) trailer; so the IP header of the original packet is not encrypted. Transport mode is usually used when another tunneling protocol (such as [[VPN#GRE_Tunnel|GRE]], [[VPN#L2TP|L2TP]]) is used to first encapsulate the IP data packet, then IPsec is used to protect the GRE/L2TP tunnel packets. | It should also be noted the connection type used is '''Tunnel''' and not '''Transport'''. Tunnel protects the internal routing information by encrypting the IP header of the original packet. The original packet is encapsulated by a another set of IP headers. Transport encrypts only the payload and Encapsulating Security Payload (ESP) trailer; so the IP header of the original packet is not encrypted. Transport mode is usually used when another tunneling protocol (such as [[VPN#GRE_Tunnel|GRE]], [[VPN#L2TP|L2TP]]) is used to first encapsulate the IP data packet, then IPsec is used to protect the GRE/L2TP tunnel packets. |