UTT Technologies Chapter 12 VPN
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12.1.1.2
Packet Flow - PPTP
Figure 12-2 PPTP Packet Flow
As shown in Figure 12-2, during the PPTP tunnel establishment and data transmission
processes, the packet flow through the PPTP can be summarized as follows:
1. After the PPTP tunnel parameters are configured properly, the PPTP automatically
creates a virtual interface for the new tunnel to listen for user data ((1) in Figure 12-2).
2. The PPTP
’s virtual interface listens for the user packets destined for the remote LAN
((3) in Figure 12-2).
3. The PPTP initiates the PPTP tunnel setup request ((4) in Figure 12-2).
4. The PPTP receives the user authentication request from the PPTP server, and then
responds to the request ((7) in Figure 12-2).
5. The PPTP negotiates with the PPTP server to establish a PPTP tunnel ((8) in Figure
12-2).
6. The PPTP receives the user data (i.e., original packets) and encapsulates them in the
PPP frames ((9) in Figure 12-2).
7. The PPTP sends the PPTP packets to the PPTP server through the PPTP tunnel ((10)
in Figure 12-2).