IPsec

A protocol in development by the IETF to support secure data exchange. Once completed, IPSec is expected to be widely deployed to implement virtual private networks (VPNs). IPSec supports two encryption modes: Transport and Tunnel. Transport mode encrypts the data portion (payload) of each packet but leaves the header untouched. Tunnel mode is more secure because it encrypts both the header and the payload. On the receiving side, an IPSeccompliant device decrypts each packet.
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A mode of IPSec when used in a VPN. In transport mode, the IP packet data is encrypted but the header of the packet is not. An IPSec protocol used with ESP or Alt in which the ESP or Alt header is inserted between the IP header and the upperlayer protocol of an IP packet.
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A protocol that provides background security support services for IPSec.
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A protocol that provides for the secure exchange of cryptographic keys between IPSec participants.
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(1) Layer 2 of the OSI Reference Model. Provides reliable transit of data across a physical link. The datalink layer is concerned with physical addressing, network topology, line discipline, error notification, ordered delivery of frames, and flow control. The IEEE divided this layer into two sublayers: the MAC sublayer and the LLC sublayer. Sometimes simply called the link layer. Roughly corresponds to the datalink control layer of the SNA model. (2) A layer with the responsibility of transmitting data reliably across a physical link (cabling, for example) using a networking technology such as Ethernet. The DLL encapsulates data into frames (or cells) before it transmits it. It also enables multiple computer systems to share a single physical medium when used in conjunction with a media access control methodology such as CSMA/CD.
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