How do I set up PPP in LINUX?

In the voluntary tunnel model, a tunnel is created by the user, typically by the use of a L2TP enabled client which is called as LAC client. The user will send L2TP packets to the Internet Service Provider (ISP) which will forward them on to the LNS. The ISP does not need to support L2TP, it only forwards the L2TP packets between LAC and LNS . The LAC client acts as a L2TP tunnel initiator which effectively resides on the same system as the remote client. The tunnel extends across the entire PPP session from the L2TP client to the LNS.