IPsec (Internet Protocol Security) is a protocol suite that provides secure communication over Internet Protocol (IP) networks. It achieves this by authenticating and encrypting each IP packet within a communication session. One of the key concepts in IPsec is the establishment of security associations (SAs) between peers. Security associations are the combination of algorithms and keys used to secure communication between two devices. They define the security parameters for the communication, including the encryption algorithm, integrity algorithm, and keying information. By establishing these security associations, IPsec ensures confidentiality, integrity, and authenticity of the data being transmitted between network nodes.