Description of LAC and LNS of the L2TP on firewalls

L2TP access concentrator (LAC): It is a device attached to the switching network. The LAC has a PPP terminal system and delivers L2TP processing. It usually provides access services for PPP users.

The LAC is located between the L2TP network server (LNS) and a user, used to transfer information packets between the LNS and the user. The LAC encapsulates the information packets received from the user based on L2TP and delivers the information packets to the LNS. In addition, it decapsulates information packets received from the LNS and delivers the information packets to the user.

The LAC and the user are connected in local connection mode or over a PPP link. In the VPDN application scenario, the LAC and the user are connected over the PPP link.

LNS: It is both a logical termination point of a PPP system and an L2TP server. Generally, it serves as an edge on the enterprise intranet.

As one side of an L2TP tunnel endpoint, the LNS is a peer to the LAC. The LNS is the logical termination point of a PPP session that is being tunneled from the remote system by the LAC. By establishing an L2TP tunnel on the public network, the peer end of a PPP session is logically extended from the LAC to the LNS on the enterprise intranet.

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