Internet Protocol Security. Provides security to IP flows through the use of authentication and encryption:

• Authentication verifies that data is not altered during transmission and ensures that users are communicating with the individual or organization that they believe they are communicating with.
• Encryption makes data confidential by making it unreadable to everyone except the sender and intended recipient.

Internet Protocol version 4. Network Layer (Layer 3) connectionless protocol for the routing of datagrams through gateways connecting networks and subnetworks. It is used on packet switched internetworks, for example, Ethernet.

Internet Protocol version 6. IPv6 is the next planned version of the IP address system, to eventually supersede IP version 4 (IPv4). While IPv4 uses 32-bit addresses, IPv6 uses 128-bit addresses, which increases the number of possible addresses exponentially. For example, IPv4 allows 4,294,967,296 addresses to be used (2^32). IPv6 allows for over 340,000,000,000,000,000,000,000,000,000,000,000,000 IP addresses. It can be installed as a normal software upgrade in Internet devices and is interoperable with the current IPv4. Also known as IPng (for IP next generation). See also IP address.

Internet Key Exchange. Part of IPsec that provides ways to exchange keys for encryption and authentication securely over an unsecured medium such as the Internet. IKE enables a pair of security gateways to:

• Dynamically establish a secure tunnel over which security gateways can exchange tunnel and key information.
• Set up user-level tunnels or SAs, including tunnel attribute negotiations and key management. These tunnels can also be refreshed and terminated on top of the same secure channel.

IKE employs Diffie-Hellman methods and is optional in IPsec (the shared keys can be entered manually at the endpoints).

security association. Set of security parameters that dictates how IPsec processes a packet. The SA defines what rules to use for authentication and encryption algorithms, key exchange mechanisms, and secure communications between two parties. A single secure tunnel uses multiple SAs. See also SA parameters.