Assumptions: Compulsory tunneling
The Client initiates a PPP connection to the LAC.
The LAC does LCP negotiation with the client, and challenges the client for authentication credentials.
The client supplies the credentials (such as user name, domain name, password).
The LAC uses the domain name to ascertain which LNS it needs to contact (in the case of multiple domains).
The LAC begins establishing an L2TP tunnel with the LNS.
Two Stages of L2TP Tunnel Setup:
Set up a control session between the LAC and the LNS.
Set up the actual L2TP tunnel for passing the data (aka. ‘creating the session’)
Between a pair of LAC and LNS, there may exist multiple tunnels.
Across a single L2TP tunnel, there may exist multiple sessions.