Internet Protocol Security IPSec is actually a suite of protocols. Each protocol within the suite provides different fu…

IPSec is a suite of protocols that provide security services at IP layer of TCP/IP stack i.e. Network Layer in OSI model. As Andy Lemke mentioned, IPSec suite comprises of two protocols to offer security to 1. AH - Authentication Header Protocol.(Protocol no: 51) 2. ESP - Encapsulation of security payload Protocol. (Protocol no:50) AH provides authentication, integrity and anti-replay services at Network Layer and above. ESP provides authentication, integrity, anti-replay and confidentiality services at Transport Layer and above. Hence, we can say, IPSec(AH+ESP) operates at Network Layer and provide security services at Network and above layers. A note on IKE protocol Its imperative that, if two entities want to communicate securely, they should share secret keys to set up a secure connection, encrypt and decrypt messages etc. Hence, Apart from AH and ESP , most of the IPSec implementations also use a Key exchange and management protocol that generates, negotiates and manages secret keys for establishing a secure channel between communicating entities. This key exchange protocol is called IKE - Internet Key exchange protocol.