A Virtual Private Network is an encrypted "tunnel" from an untrusted network such as the Internet into a trusted network, such as an organization's Internal network. ISA Server 2004 possesses a wide array of VPN capabilities, all of which can be accessed through the Virtual Private Networks Node in the ISA Server Console, as shown in Figure 3.25
Figure 3.25. Examining the Virtual Private Networks (VPNs) node in the ISA Console.
This section of the chapter covers the ISA Server Console settings in the VPN node at a high level, describing the general options available and giving an idea of what VPN tools are available in the console. For advanced VPN design, configuration, and step-by-step descriptions, see Chapters 9 and 10, "Extending ISA Server 2004 to Branch Offices with Site-to-Site VPNs."
Enabling and Configuring VPN Client Access
By default, VPN access through ISA Server is not enabled, and it must be turned on before VPN capabilities can be reviewed. Turning on VPN functionality is a straightforward process and can be performed as follows:
The VPN functionality of ISA Server relies on the Routing and Remote Access Service of Windows Server 2003, and requires it to be started for VPN clients to be able to connect. If a Security Policy is in place to disable this service, it will create problems with VPNs, so it is subsequently important to validate that RRAS functionality is enabled if the ISA Server will need to process VPN requests.
After VPN client access has been granted, the VPN client settings can be configured by clicking on the Configure VPN Client Access link in the Task Pane. This link invokes the VPN Clients Properties dialog box, shown in Figure 3.27, where the following settings can be configured:
Figure 3.27. Setting VPN client properties.
Configuring Remote Access Configuration
Many of the options associated with VPNs in ISA Server can be found in the Remote Access configuration dialog box, accessible via the Select Access Networks link in the Task pane. The dialog box invoked via this link, shown in Figure 3.28, allows for the configuration of Remote Access properties specific to VPN access, but not necessarily specific to clients. These include the following settings:
Figure 3.28. Configuring Remote Access settings.
Creating Remote Site Networks for Site-to-Site VPN
ISA Server 2004 also includes the capability to create encrypted tunnels between two disparate networks in an organization that are connected through the Internet. This allows for communication across the Internet to be scrambled so that it cannot be read by a third party. ISA provides this capability through its Remote Site VPN capabilities.
The Remote Site VPN options, available on the Remote Sites tab in the Central Details pane of the VPN node, allow for the creation and configuration of Remote Site networks for site-to-site VPNs. These site-to-site VPN networks enable an organization to connect remote networks together, creating one complete, routable, and logical network, such as the one shown in Figure 3.29.
Figure 3.29. Configuring Remote Access settings.
When configuring a site-to-site VPN between two ISA Server 2004 systems, the option exists to secure the traffic by using the IP Security Protocol (IPSec), the Later Two Tunneling Protocol (L2TP) over IPSec, or the Point-to-Point Tunneling Protocol (PPTP), depending on the individual organizational security needs. These options are available when running the New Site-to-Site Network Wizard that is launched from the Add Remote Site Network link in the Task pane.
In addition to supporting a destination ISA Server 2004 system for site-to-site VPN, ISA Server also supports connecting to a third-party VPN Gateway that supports the IPSec protocol. This greatly extends ISA's reach because third-party firewall solutions that may already be in place are potential candidates for ISA site-to-site VPNs.
Specific configuration information for site-to-site VPNs can be found in Chapter 10.
Understanding VPN Quarantine
The concept of the VPN quarantine network is fairly straightforward; although, its implementation is not necessarily so. Essentially, VPN quarantine refers to the capability to have ISA place a client that does not conform to specific criteria into a special quarantined VPN clients network. This network can then be limited to only a specific set of low-risk activities. For example, it may be useful to validate that all clients have approved anti-virus software installed before full access to the network is granted.
VPN quarantine is not on by default, and must be specifically set up and configured. Chapter 9 contains step-by-step procedures, but the configuration of VPN quarantine consists of two processes. The first process involves configuring VPN client computers with a special listener that reports to the ISA server if the client passes specified criteria that are necessary for full access. The second component, illustrated in Figure 3.30, involves checking the box in the Quarantined VPN Clients Properties dialog box.
Figure 3.30. Enabling VPN quarantine.
Unlike the other VPN settings, you can invoke this dialog box in the Networks node by double-clicking on the quarantined VPN clients network listed under the Networks tab of the Central Details pane.