L2TP Terminology
Table 1 describes the basic terms for L2TP.
Table 1: L2TP Terms
Term | Description |
|---|---|
AVP | Attribute value pair (AVP)—Combination of a unique attribute—represented by an integer—and a value containing the actual value identified by the attribute. |
Call | A connection (or attempted connection) between a remote system and the LAC. |
LAC | L2TP access concentrator (LAC)—A node that acts as one side of an L2TP tunnel endpoint and is a peer to the LNS. The LAC sits between an LNS and a remote system and forwards packets to and from each. |
LNS | L2TP network server (LNS)—A node that acts as one side of an L2TP tunnel endpoint and is a peer to the LAC. The LNS is the logical termination point of a PPP connection that is being tunneled from the remote system by the LAC. |
Peer | In the L2TP context, either the LAC or LNS. The LAC’s peer is an LNS, and vice versa. |
Proxy authentication | PPP pre-authentication performed by the LAC on behalf of the LNS. The proxy data is sent by the LAC to the LNS containing attributes such as authentication type, authentication name, and authentication challenge. The LNS responds with the authentication results. |
Proxy LCP | Link Control Protocol (LCP) negotiation that is performed by the LAC on behalf of the LNS. The proxy is sent by the LAC to the LNS containing attributes such as the last configuration attributes sent and received from the client. |
Remote system | An end system or router attached to a remote access network, which is either the initiator or recipient of a call. |
Session | A logical connection created between the LAC and the LNS when an end-to-end PPP connection is established between a remote system and the LNS. Note: There is a one-to-one relationship between established L2TP sessions and their associated PPP connections. |
Tunnel | A connection between the LAC-LNS pair consisting of a control connection and 0 or more L2TP sessions. |
