How does IPsec relate to VPNs?
IPSec is an evolving standard for secure private communications over the Internet. A set of protocols developed by the IETF to support secureexchangeof packets at the IP layer, and has seen a tremendous growth and widespread deployment with the advent of VPNs. IPsec supports two encryption modes: Transport and Tunnel. Transport mode encrypts only the data portion (payload) of each packet, but leaves the header untouched. The more secure Tunnel mode encrypts both the header and the payload. On the receiving side, an IPSec-compliant device decrypts each packet. For IPsec to work, the sending and receiving devices must share a public key. This is accomplished through a protocol known as Internet Security Association and Key Management Protocol/Oakley (ISAKMP/Oakley), which allows the receiver to obtain a public key and authenticate the sender using digital certificates. Normal IPv4 packets consist of headers and payload, both of which contain information of value to an attacker. The heade
