Chapter 3. IP Security Overview
IP Packets have no inherent security. It is relatively easy to forge the addresses of IP packets, modify the contents of IP packets, replay old packets, and inspect the contents of IP packets in transit. Therefore, there is no guarantee that IP datagrams received are (1) from the claimed sender (the source address in the IP header); (2) that they contain the original data that the sender placed in them; or (3) that the original data was not inspected by a third party while the packet was being sent from source to destination. IPSec is a method of protecting IP datagrams. This protection takes the form of data origin authentication, connectionless data integrity authentication, and data content confidentiality.