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Using Virtual Private Network Connections in Windows Vista

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Virtual Private Networks offer secure access to a private network over a public connection. Paul McFedries explains the background and operation of VPNs in Windows Vista.
This chapter is from the book

This chapter is from the book

In the remote connections you've seen so far, the security exists mostly at the connection point. That is, you set up usernames with strong passwords, and no one can access your dial-up or Remote Desktop connection without entering the correct logon data. This works well, but it doesn't do much for the actual data that's passed between the host and client. A malicious hacker might not be able to access your system directly, but he certainly can use a packet sniffer or similar technology to access your incoming and outgoing data. Because that data isn't encrypted, the hacker can easily read the contents of the packets.

What do you do, then, if you want to transfer secure data such as financial information or personnel files, but you love the simplicity of a dial-up connection? The answer is a tried-and-true technology called virtual private networking (VPN), which offers secure access to a private network over a public connection, such as the Internet or a phone line. VPN is secure because it uses a technique called tunneling, which establishes a connection between two computers—a VPN server and a VPN client—using a specific port (such as port 1723). Control-connection packets are sent back and forth to maintain the connection between the two computers (to, in a sense, keep the tunnel open).

When it comes to sending the actual network data—sometimes called the payload—each network packet is encrypted and then encapsulated within a regular IP packet, which is then routed through the tunnel. Any hacker can see this IP packet traveling across the Internet, but even if he intercepts the packet and examines it, no harm is done because the content of the packet—the actual data—is encrypted. When the IP packet arrives on the other end of the tunnel, VPN decapsulates the network packet and then decrypts it to reveal the payload.

Windows Vista comes with VPN client support built in and it uses two tunneling protocols:

Point-to-Point Tunneling Protocol (PPTP)

This protocol is the most widely used in VPN setups. It was developed by Microsoft and is related to the Point-to-Point Protocol (PPP) that's commonly used to transport IP packets over the Internet. A separate protocol—Microsoft Point-to-Point Encryption (MPPE)—encrypts the network packets (IP, IPX, NetBEUI, or whatever). PPTP sets up the tunnel and encapsulates the encrypted network packets in an IP packet for transport across the tunnel.

IP Security (IPSec)

This protocol encrypts the payload (IP packets only), sets up the tunnel, and encapsulates the encrypted network packets in an IP packet for transport across the tunnel.

There are two main ways to use VPN:

Via the Internet

In this case, you first connect to the Internet using any PPP-based dial-up or broadband connection. Then you connect to the VPN server to establish the VPN tunnel over the Internet.

Via a dial-up connection

In this case, you first connect to the host computer using a regular dial-up connection. Then you connect to the VPN server to establish the VPN tunnel over the telephone network.

Configuring a Network Gateway for VPN

The best way to use VPN is when the client has a broadband Internet connection and the server has a public IP address or domain name. This enables you to access the server directly using your fast Internet connection. What happens, however, if the Windows Vista machine you set up as the VPN server sits behind a gateway or firewall and so uses only an internal IP address (192.168.1.*)?

You can often get around this problem by setting up a network gateway to pass through VPN packets and forward them to the VPN server. (Note that some broadband routers come with VPN capabilities built in, so they can handle an incoming VPN connection automatically.)

The details depend on the device, but the usual first step is to enable the gateway's support for VPN passthrough, which allows network computers to communicate via one or more VPN protocols (such as PPTP and IPSec). Figure 24.10 shows a sample page in a gateway setup application that that lets you enable passthrough for the IPSec, PPTP, and L2TP protocols.


Figure 24.10 In your gateway setup application, enable VPN passthrough for the protocols you use.

In some cases, just enabling VPN passthrough is all you need to do to get VPN up and running through your gateway. If your VPN connection doesn't work or if your gateway doesn't support VPN passthrough, you have to open a port for the VPN protocol you're using and then have data to that port forwarded to the VPN server.(This is similar to the port forwarding described earlier for Remote Desktop connections.) The forwarded ports depend on the protocol:


Forward TCP to port 1723


Forward UPD to port 500

Figure 24.11 shows an example of port forwarding.


Figure 24.11 In your gateway setup application, forward the ports of the VPN protocols you use to the IP address of your network's VPN server.

Configuring the VPN Client

Now you have to configure the remote computer as a VPN client. Here are the steps to follow:

  1. Select Start, Connect To. Vista displays the Connect to a Network dialog box.
  2. Click the Set Up a Connection of Network link to open the Choose a Connection Option dialog box.
  3. Click Connect to a Workplace and then click Next. The How Do You Want to Connect? dialog box appears.
  4. Click one of the following two choices: Use My Internet Connection—Click this option if you want to make the VPN connection over the Internet. Dial Directly—Click this option to use a dial-up VPN connection.
  5. In the next dialog box (Figure 24.12 shows the Internet connection version), configure the following controls (click Next when you're done):

    Figure 24.12 Use this dialog box to specify the location of your network's VPN server and other connection options.

    • Internet Address— If you're using an Internet connection, type the domain name or IP address of the VPN server (or the network gateway that forwards your connection to the VPN server).
    • Telephone Number— If you're using a dial-up connection, type the phone number used by the VPN server.
    • Destination Name— Type a name for the VPN connection.
    • Use a Smart Card— Activate this check box if your VPN server requires you to have a smart card security device inserted in your system as part of the server's authentication process.
    • Allow Other People to Use This Connection— Activate this check box to make this connection available to other user accounts on your computer.
    • Don't Connect Now— Activate this check box to prevent Vista from connecting to the VPN server right away. This is useful if you're just setting up the connection for later use.
  6. Type your VPN logon data: your username, your password, and your network domain (if any).
  7. Click Create. Vista creates the connection and launches it (unless you activated the Don't Connect Now check box in step 5).
  8. Click Close.

Windows Vista adds a Virtual Private Network group to the Network Connections folder, and places in that group an icon with the name you specified in step 5.

Making the VPN Connection

With the VPN client configured, you can now use the client to make the VPN connection. Follow these steps on the VPN client computer:

  1. If you need to establish a dial-up connection to the Internet before connecting to the VPN server, make that connection now.
  2. Select Start, Connect To.
  3. Scroll up the Dial-up and VPN group.
  4. Click the VPN connection and then click Connect. The Connect dialog box appears for the VPN connection. Type your username, password, and domain (if applicable).
  5. If you want Windows Vista to remember your logon data, activate the Save This User Name and Password for the Following Users, and then activate either Me Only or Anyone Who Uses this Computer.
  6. Click Connect. Windows Vista sets up the VPN connection.
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