http://www.rfc-editor.org/rfc/rfc2661.txt
RFC 2661: Layer Two Tunneling Protocol "L2TP", W. Townsley, A. Valencia, A. Rubens, G. Pall, G. Zorn, B. Palter1999-08-01T23:00:00-00:00This document describes the Layer Two Tunneling Protocol (L2TP). [STANDARDS-TRACK]