TS Gateway, ISA Server, and NAP Working Better Together

Terminal Services–based remote access has long been used as a simpler, lower-risk alternative to classical layer 2 VPN technologies. Whereas the layer 2 VPN has often provided “all ports, all protocols” access to an organization’s internal network, the Terminal Services approach restricts connectivity to a single well-defined port and protocol. However, as more and more capability has ascended the stack into RDP (such as copy/paste and drive redirection), the potential attack vectors have risen as well. For example, a remote drive made available over RDP can present the same kinds of security risks as one mapped over native CIFS/SMB transports.

With the advent of TS Gateway, allowing workers to be productive from anywhere has never been easier. TS Gateway also includes several powerful security capabilities to make this access secure. In addition to its default encryption and authentication capabilities, TS Gateway can be combined with ISA Server and Network Access Protection to provide a secure, manageable access method all the way from the client, through the perimeter network, to the endpoint terminal server. Combining these technologies allows an organization to reap the benefits of rich RDP-based remote access, while mitigating the potential exposure this access can bring.

ISA Server adds two primary security capabilities to the TS Gateway solution. First, because it can act as an SSL terminator, it allows for more secure placement of TS Gateway servers. Because ISA can be the Internet-facing endpoint for SSL traffic, the TS Gateway itself does not need to be placed within the perimeter network. Instead, the TS Gateway can be kept on the internal network and the ISA Server can forward traffic to it. However, if ISA were simply performing traffic forwarding, it would be of little real security benefit. Thus, the second main security value ISA brings to the solution is pre-authentication capabilities. Rather than simply terminating SSL traffic and forwarding frames on to the TS Gateway, ISA authenticates users before they ever contact the TS Gateway, ensuring that only valid users are able to communicate with it. Using ISA as the SSL endpoint and traffic inspection device allows for better placement of TS Gateway resources and ensures that they receive only inspected, clean traffic from the Internet.

Although ISA Server provides important network protection abilities to a TS Gateway solution, it does not address client-side threats. For example, users connecting to a TS Gateway session might have malicious software running on their machines or be non-compliant with the organization’s security policy. To mitigate against these threats, TS Gateway can be integrated with Network Access Protection to provide enforcement of security and healthy policies on these remote machines.

NAP is included in Windows Server 2008 and can be run on the same machine as TS Gateway, or TS Gateway can be configured to use an existing NAP infrastructure running elsewhere. When combined with TS Gateway, NAP provides the same policy-based approach to client health and enforcement as it does on normal (not RDP-based) network connections. Specifically, NAP can control access to a TS Gateway based on a client’s security update, antivirus, and firewall status. For example, if you choose to enable redirected drives on your terminal servers, you might require that clients have antivirus software running and up to date. NAP allows organizations to ensure that computers connecting to a TS Gateway are healthy and compliant with its security policies.

Source of Information : Introducing Windows Server 2008

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