1.3 Overview
Layer 2 Tunneling Protocol (L2TP) Internet Protocol security (IPsec) Extensions (L2TPIE) provides extensions to the Layer 2 Tunneling Protocol (L2TP) specification [RFC2661] and to securing L2TP using IPsec [RFC3193] in order to provide traceability and data control flow features. In this extension a new Microsoft vendor-specific attribute value pair (AV pair) is sent in control messages from the LAC/client to the LNS/server so that tracing events on the server specific to a client can be correlated. This extension uses the data control flow mechanism specified in [L2TP-draft].
L2TPIE defines additional AV pairs other than those defined in L2TP. It also defines changes to the behavior in processing messages or AV Pairs other than those that are defined in the L2TP specification [RFC2661]. These extensions also define subset of [RFC3193]. For example, support for changing the IP address and port is restricted.
See [RFC2661] section 1 for an introduction to L2TP. [RFC3193] specifies an Internet Engineering Task Force (IETF) standard protocol designed to use IPsec [RFC2401] to provide for tunnel authentication, privacy protection, and integrity checking and replay protection of L2TP.