计算机网络系列（11）之应用场景Virtual Private Networks

1. Virtual private networks
Virtual private networks are used by many organizations and individuals for different purposes.

1.1. Site-to-site VPN
Each site is connected to the Internet via a VPN router.

1.2. Point-to-point VPN
Run a VPN server where this server is not blocked from accessing the associated servers.

1.3. Better security

1.4. VPN protocols
PPTP, L2TP/IPSec, OpenVPN, SSL, SSH

2. Questions
Q1: State the possible functions of VPNs.
internal meetings/remote desktop connection

Q2: Consider the following two cases:
− Case 1: Peter uses his smart phone to directly access a
website.
− Case 2: Peter uses his smart phone to access the same
website via VPN.
Give three reasons to explain why Case 2 is slower.

reason1: Data encryption is time-consuming
reason2: Not direct access, but indirect access
reason3: The VPN server may be in a far-away place

Q3: In the following site-to-site VPN, a source computer sends an IP datagram to a destination computer.

Source IP: IPx
Destination IP: IPy

Q4: In the following point-to-point VPN, a user’s computer sends an IP datagram to a remote server computer through a VPN server.

When the VPN server sends this IP datagram to the remote server,
what are the following quantities in this datagram:

Source IP: IP2
Destination IP: IP3

3. 总结
重点1：VPN分类上站对站，点对点的类型讨论。

重点2：VPN数据包数据加密，源IP和目标IP不加密等特点以及应用。