tailieunhanh - netscreen concepts examples vpns phần 10

Không có phần nào của cuốn sách này có thể được sao chép, lưu trữ trong một hệ thống thu hồi, hoặc truyền đi dưới bất kỳ hình thức nào hoặc bằng bất cứ phương tiện nào, mà không cần sự cho phép trước bằng văn bản của nhà xuất bản, ngoại trừ trong trường hợp các trích dẫn ngắn gọn trong phần đánh giá quan trọng hoặc các sản phẩm nhúng. | 5 L2TP This chapter provides an introduction to Layer 2 Tunneling Protocol L2TP its use alone and with IPSec support and then some configuration examples for L2TP and L2TP-over-IPSec Introduction to L2TP on page 234 Packet Encapsulation and Decapsulation on page 238 L2TP Parameters on page 240 - Example Configuring an IP Pool and L2TP Default Settings on page 241 L2TP and L2TP-Over-IPSec on page 243 - Example Configuring L2TP on page 244 - Example Configuring L2TP-over-IPSec on page 250 NetScreen Concepts Examples - Volume 4 VPNs 233 Chapter 5 L2TP Introduction to L2TP Introduction to L2TP Layer 2 Tunneling Protocol L2TP provides a way for a dial-up user to make a virtual Point-to-Point Protocol PPP connection to an L2TP network server LNS which can be a NetScreen device. L2TP sends PPP frames through a tunnel between an L2TP access concentrator LAC and the LNS. Originally L2TP was designed so that a LAC residing at an ISP site tunneled to an LNS at either another ISP or corporate site. The L2TP tunnel did not extend completely to the dial-up user s computer but only to the LAC at the dial-up user s local ISP. This is sometimes referred to as a compulsory L2TP configuration. L2TP Access L2TP Tunnel L2TP Network Concentrator forwarding PPP sessions Server LAC -------- from LAC to LNS -------------- LNS With the capability of a NetScreen-Remote client on Windows 2000 or Windows NT or a Windows 2000 client by itself to act as a LAC the L2TP tunnel can extend directly to the dial-up user s computer thus providing end-to-end tunneling. This approach is sometimes referred to as a voluntary L2TP configuration. NetScreen Concepts Examples - Volume 4 VPNs 234 Chapter 5 L2TP Introduction to L2TP NetScreen Device NetScreen-Remote or Windows 2000 L2TP Tunnel forwarding PPP sessions from lAc to LNS Corporate Because the PPP link extends from the dial-up user across the Internet to the NetScreen device LNS it is the NetScreen device not the ISP that assigns the client its IP .