VPN technology detailed (the next)

VPN technology detailed (the next)
Lu Xiaopo
(Immediately medium)

Data transfer phase
Once this 4-phase negotiation is complete, PPP begins forwarding data between the connecting peers. Each transmitted datagram is encapsulated within the PPP header, which is removed after it arrives at the receiving party. If you choose to use data compression in Phase 1 and you have completed the negotiation in Phase 4, the data will be compressed between transfers. Similarly, if you have chosen to use data encryption and have completed the negotiation, the data (or compressed data) will be encrypted before the transfer.
Point to Point Tunneling Protocol (PPTP)
PPTP is a layer 2nd protocol that encapsulates a PPP data frame in an IP datagram over an IP network, such as the Internet. PPTP can also be used for connections between private local area networks. The draft RFC "Point-to-Point Tunneling Protocol" describes and introduces the PPTP protocol. The draft was submitted to the IETF by member companies of the PPTP forum, including Microsoft, Ascend,3com, and ECI, in June 1996. You can see the online copy of the draft at the following site http://www.ietf.org http://www.ietf.org. PPTP maintains a tunnel using a TCP connection and uses Universal Routing Encapsulation (GRE) technology to encapsulate data into a PPP data frame for transmission through the tunnel. Load data in the encapsulated PPP frame can be encrypted or compressed. Figure 7 shows how to assemble a PPTP packet before the data is delivered.
Layer 2nd Forwarding (L2F)
L2F is Cisco's proposed tunneling technology, as a transport protocol L2F supports dial-up access servers that encapsulate dial-up data flows through a WAN link to a L2F server (router) in a PPP frame. L2F the server to unpack the packets (inject) network. Unlike PPTP and L2TP, L2F does not have a defined client side. It should be noted that L2F is only valid in forced tunnels. (The introduction of voluntary and mandatory tunnels is referred to "tunnel type").
Layer 2nd Tunneling Protocol (L2TP)
L2TP combines the PPTP and L2F protocols. The designer wants L2TP to combine the advantages of PPTP and L2F.
L2TP is a network layer protocol that supports the transmission of encapsulated PPP frames on networks such as ip,x.25, hardwood relay or ATM. When using IP as the datagram transport protocol for L2TP, you can use L2TP as a tunneling protocol on an Internet network. L2TP can also be used directly on a variety of WAN media without the need to use an IP transport layer. The draft RFC "2nd-Tier Tunneling Protocol" provides a description and introduction to L2TP. The document was submitted to the IETF in January 1998. A copy of the draft can be obtained at the following website http://www.ietf.org http://www.ietf.org.
L2TP on the IP network maintain the tunnel using UDP and a series of L2TP messages. L2TP also uses UDP to send a PPP frame encapsulated by the L2TP protocol through the tunnel. Load data in the encapsulated PPP frame can be encrypted or compressed. Figure 8 shows how to assemble a L2TP packet before transmission.
PPTP and L2TP
Both PPTP and L2TP use the PPP protocol to encapsulate data and then add additional headers for data transmission over the Internet. Although the two protocols are very similar, there are several differences: