Technical Overview of DirectAccess in Windows 7 and Windows

Technical Overview of DirectAccess in Windows 7 and Windows
Technical Overview of DirectAccess in
Windows 7 and Windows Server 2008 R2
Microsoft Windows Family of Operating Systems
Microsoft Corporation
Published: April 2009
Abstract
The Windows 7 and Windows Server 2008 R2 operating systems introduce DirectAccess, a
solution that provides users with the same experience working remotely as they would have when
working in the office. With DirectAccess, remote users can access corporate file shares, Web
sites, and applications without connecting to a virtual private network (VPN).
Copyright information
This document supports a preliminary release of a software product that may be changed
substantially prior to final commercial release. This document is provided for informational
purposes only and Microsoft makes no warranties, either express or implied, in this document.
Information in this document, including URL and other Internet Web site references, is subject to
change without notice. The entire risk of the use or the results from the use of this document
remains with the user. Unless otherwise noted, the companies, organizations, products, domain
names, e-mail addresses, logos, people, places, and events depicted in examples herein are
fictitious. No association with any real company, organization, product, domain name, e-mail
address, logo, person, place, or event is intended or should be inferred. Complying with all
applicable copyright laws is the responsibility of the user. Without limiting the rights under
copyright, no part of this document may be reproduced, stored in or introduced into a retrieval
system, or transmitted in any form or by any means (electronic, mechanical, photocopying,
recording, or otherwise), or for any purpose, without the express written permission of Microsoft
Corporation.
Microsoft may have patents, patent applications, trademarks, copyrights, or other intellectual
property rights covering subject matter in this document. Except as expressly provided in any
written license agreement from Microsoft, the furnishing of this document does not give you any
license to these patents, trademarks, copyrights, or other intellectual property.
© 2009 Microsoft Corporation. All rights reserved.
Microsoft, Internet Explorer, Outlook, Windows, Windows Server, and Windows Vista are
trademarks of the Microsoft group of companies. All other trademarks are property of their
respective owners.
Contents
DirectAccess Technical Overview for Windows 7 and Windows Server 2008 R2 ......................... 5
Mobile Workforce Needs ................................................................................................................. 6
The Challenges with VPNs .............................................................................................................. 6
DirectAccess Connections ............................................................................................................... 6
End-to-end protection ................................................................................................................... 8
End-to-edge protection ................................................................................................................. 8
The DirectAccess Connection Process ........................................................................................... 9
Separating Internet and Intranet Traffic ......................................................................................... 10
DirectAccess Authentication .......................................................................................................... 11
Using IPv6 ..................................................................................................................................... 12
DirectAccess and Network Access Protection .............................................................................. 12
DirectAccess Requirements .......................................................................................................... 12
Summary ....................................................................................................................................... 13
References .................................................................................................................................... 14
DirectAccess Technical Overview for
Windows 7 and Windows Server 2008 R2
The Windows® 7 and Windows Server® 2008 R2 operating systems introduce DirectAccess, a
new solution that provides users with the same experience working remotely as they would have
when working in the office. With DirectAccess, remote users can access corporate file shares,
Web sites, and applications without connecting to a virtual private network (VPN).
DirectAccess establishes bi-directional connectivity with the user’s enterprise network every time
the user’s DirectAccess-enabled portable computer is connected to the Internet, even before the
user logs on. With DirectAccess, users never have to think about whether they are connected to
the corporate network. DirectAccess also benefits IT by allowing network administrators to
manage remote computers outside of the office, even when the computers are not connected to a
VPN. DirectAccess enables organizations with regulatory concerns to extend regulatory
compliance to roaming computer assets.
This document describes the benefits of DirectAccess, how it works, and what you will need to
deploy it in your organization. The following topics are covered:
Mobile Workforce Needs
The Challenges with VPNs
DirectAccess Connections
The DirectAccess Connection Process
Separating Internet and Intranet Traffic
DirectAccess Authentication
Using IPv6
DirectAccess and Network Access Protection
DirectAccess Requirements
Summary
References
Notes

For a complete view of Windows 7 resources, articles, demos, and guidance, please visit
the Springboard Series for Windows 7 on the Windows Client TechCenter.

For a downloadable version of this document, see the DirectAccess Technical Overview
for Windows 7 and Windows Server 2008 R2 in the Microsoft Download Center
(http://go.microsoft.com/fwlink/?LinkId=151748).
5
Mobile Workforce Needs
More users have become mobile to stay productive while they are away from the office.
According to IDC, the third quarter of 2008 marked the point at which computer manufacturers
began shipping more mobile computers than desktop computers worldwide (IDC Worldwide
Quarterly PC Tracker, December 2008).
The number of mobile users is expected to grow; in 2008, mobile workers worldwide will
be 26.8% of the total workforce, and that number will increase to 30.4% by 2011 (IDC,
"Worldwide Mobile Worker Population 2007–2011 Forecast," Doc #209813, Dec 2007).
However, the way users access network resources hasn’t changed. Although home broadband,
wireless broadband, and Wi-Fi allow users to connect to the Internet while they are away from the
office, corporate firewalls prevent them from connecting to resources on the intranet. Only users
physically connected to the intranet can access intranet resources. This becomes a management
problem because IT administrators can update computers only when they connect to the intranet.
To circumvent this limitation, many organizations provide VPNs.
The Challenges with VPNs
Traditionally, users connect to intranet resources with a VPN. However, using a VPN can be
cumbersome because:

Connecting to a VPN takes several steps, and the user needs to wait for authentication. For
organizations that check the health of a computer before allowing the connection,
establishing a VPN connection can take several minutes.

Any time users lose their Internet connection, they need to re-establish the VPN connection.

VPN connections can be problematic in some environments that filter out VPN traffic.

Internet performance is slowed if both intranet and Internet traffic goes through the VPN
connection.
Because of these inconveniences, many users avoid connecting to a VPN. Instead, they use
application gateways, such as Microsoft® Outlook® Web Access (OWA), to connect to intranet
resources. With OWA, users can retrieve internal e-mail without establishing a VPN connection.
However, users still need to connect to a VPN to open documents that are located on intranet file
shares, such as those that are linked to in an e-mail message.
DirectAccess Connections
DirectAccess overcomes the limitations of VPNs by automatically establishing a bi-directional
connection from client computers to the corporate network. DirectAccess is built on a foundation
of proven, standards-based technologies: Internet Protocol security (IPsec) and Internet Protocol
version 6 (IPv6).
6
DirectAccess uses IPsec to authenticate both the computer and user, allowing IT to manage the
computer before the user logs on. Optionally, you can require a smart card for user authentication.
DirectAccess also leverages IPsec to provide encryption for communications across the Internet.
You can use IPsec encryption methods such as Triple Data Encryption Standard (3DES) and the
Advanced Encryption Standard (AES).
Clients establish an IPsec tunnel for the IPv6 traffic to the DirectAccess server, which acts as a
gateway to the intranet. Figure 1 shows a DirectAccess client connecting to a DirectAccess
server across the public IPv4 Internet. Clients can connect even if they are behind a firewall.
Figure 1 DirectAccess clients access the intranet using IPv6 and IPsec
The DirectAccess client establishes two IPsec tunnels:

IPsec Encapsulating Security Payload (ESP) tunnel using a computer certificate. This
tunnel provides access to an intranet DNS server and domain controller, allowing the
computer to download Group Policy objects and to request authentication on the user’s
behalf.

IPsec ESP tunnel using both a computer certificate and user credentials. This tunnel
authenticates the user and provides access to intranet resources and application servers. For
example, this tunnel would need to be established before Microsoft Outlook could download
e-mail from the intranet Microsoft Exchange Server.
After the tunnels to the DirectAccess server are established, the client can send traffic to the
intranet through the tunnels. You can configure the DirectAccess server to control which
applications remote users can run and which intranet resources they can access.
DirectAccess clients can connect to intranet resources by using two types of IPsec protection:
end-to-end and end-to-edge.
7
End-to-end protection
With end-to-end protection, as shown in Figure 2, DirectAccess clients establish an IPsec session
(shown in green) through the DirectAccess server to each application server to which they
connect. This provides the highest level of security because you can configure access control on
the DirectAccess server. However, this architecture requires that application servers run
Windows Server 2008 or Windows Server 2008 R2 and use both IPv6 and IPsec.
Figure 2 End-to-end protection
End-to-edge protection
For end-to-edge protection, as shown in Figure 3, DirectAccess clients establish an IPsec session
to an IPsec gateway server (which can be the same computer as the DirectAccess server). The
IPsec gateway server then forwards unprotected traffic, shown in red, to application servers on
the intranet. This architecture does not require IPsec on the intranet and works with any IPv6capable application servers.
For information about connecting to IPv4-only application servers, read Using IPv6 later in this
document.
8
Figure 3 End-to-edge protection
For the highest level of security, deploy IPv6 and IPsec throughout your organization, upgrade
application servers to Windows Server 2008 or Windows Server 2008 R2, and use end-to-end
protection. This allows authentication and, optionally, encryption from the DirectAccess client to
the intranet resources. Alternatively, use end-to-edge protection when you want to avoid
deploying both IPv6 and IPsec throughout your enterprise network. End-to-edge protection
closely resembles VPNs and, as such, can be more straightforward to deploy.
Note
For either of these architectures, you can deploy multiple DirectAccess servers with a
load balancer to meet your redundancy and scalability requirements.
The DirectAccess Connection Process
DirectAccess clients use the following process to connect to intranet resources:
1. The DirectAccess client computer running Windows 7 detects that it is connected to a
network.
2. The DirectAccess client computer attempts to connect to an intranet Web site that an
administrator specified during DirectAccess configuration. If the Web site is available, the
DirectAccess client determines that it is already connected to the intranet, and the
DirectAccess connection process stops. If the Web site is not available, the DirectAccess
client determines that it is connected to the Internet and the DirectAccess connection process
continues.
3. The DirectAccess client computer connects to the DirectAccess server using IPv6 and IPsec.
If a native IPv6 network isn’t available (and it probably won’t be when the user is connected
to the Internet), the client establishes an IPv6-over-IPv4 tunnel using 6to4 or Teredo. The
user does not have to be logged in for this step to complete.
4. If a firewall or proxy server prevents the client computer using 6to4 or Teredo from
connecting to the DirectAccess server, the client automatically attempts to connect using the
IP-HTTPS protocol, which uses a Secure Sockets Layer (SSL) connection to ensure
connectivity.
5. As part of establishing the IPsec session, the DirectAccess client and server authenticate
each other using computer certificates for authentication.
6. By validating Active Directory® group memberships, the DirectAccess server verifies that the
computer and user are authorized to connect using DirectAccess.
Note
To mitigate the risk of denial of service (DoS) attacks, IPsec on the DirectAccess
server de-prioritizes key negotiation traffic using Differentiated Services Code Points
(DSCPs).
9
7. If Network Access Protection (NAP) is enabled and configured for health validation, the
DirectAccess client obtains a health certificate from a Health Registration Authority (HRA)
located on the Internet prior to connecting to the DirectAccess server. The HRA forwards the
DirectAccess client’s health status information to a NAP health policy server. The NAP health
policy server processes the policies defined within the Network Policy Server (NPS) and
determines whether the client is compliant with system health requirements. If so, the HRA
obtains a health certificate for the DirectAccess client. When the DirectAccess client connects
to the DirectAccess server, it submits its health certificate for authentication.
For more information, see DirectAccess and Network Access Protection later in this
document.
8. The DirectAccess server begins forwarding traffic from the DirectAccess client to the intranet
resources to which the user has been granted access.
The DirectAccess connection process happens automatically, without requiring user intervention.
Separating Internet and Intranet Traffic
DirectAccess can separate intranet traffic to the intranet from Internet traffic, as shown in Figure 4,
to reduce unnecessary traffic on the corporate network. Most VPNs send all traffic—even traffic
that is destined for the Internet—through the VPN, which can slow both intranet and Internet
access. Because communications to the Internet do not have to travel to the corporate network
and back to the Internet, DirectAccess does not slow down Internet access.
Figure 4 The default traffic flow for DirectAccess does not send Internet traffic through the
DirectAccess server
IT administrators can also choose to route all traffic, except traffic for the local subnet, through the
DirectAccess server and the intranet. When this option is enabled, all communications use the IP10
HTTPS protocol, which creates an IP tunnel within the HTTPS protocol, allowing it to pass
through firewalls and proxy servers.
Combining this option with Windows Firewall with Advanced Security, IT administrators have
complete control over which applications can send traffic and which subnets client computers can
reach. For example, IT administrators can use outbound Windows Firewall rules to:

Allow client computers to connect to the entire Internet, but only one specific subnet on the
intranet.

Allow client computers to connect directly to the Internet using Internet Explorer®, but send
traffic for all other applications through the intranet.

Prevent intranet applications from sending communications to the Internet by restricting them
to specific servers on your intranet.
While the default DirectAccess traffic configuration is optimized for performance, IT administrators
have the flexibility they need to meet their organization’s security requirements.
DirectAccess Authentication
DirectAccess authenticates the computer before the user logs on. Typically, computer
authentication grants access only to domain controllers and DNS servers. After the user logs on,
DirectAccess authenticates the user, and the user can connect to any resources he or she is
authorized to access.
DirectAccess supports standard user authentication using a user name and password. For
greater security, you can implement two-factor authentication with smart cards. Typically, this
requires a user to insert a smart card in addition to typing his or her user credentials. Smart card
authentication prevents an attacker who acquires a user’s password (but not the smart card) from
connecting to the intranet. Similarly, an attacker who acquires the smart card but does not know
the user’s password is unable to authenticate.
You can require smart card authentication in the following configurations:

User authentication. Smart card authentication is required for specified users, regardless of
which computer they use.

Computer authentication. Smart card authentication is required for specified computers,
regardless of which user logs on.

Gateway authentication. The IPsec gateway requires smart card authentication before
allowing connectivity. This type of configuration allows users to access Internet resources
without their smart card, but requires a smart card before users or computers can connect to
intranet resources. This can be combined with either of the previous smart card
authentication scenarios. When smart card authentication is required for end-to-end
authentication, you must use Active Directory Domain Services (AD DS) in Windows
Server 2008 R2.
11
Using IPv6
DirectAccess requires the use of IPv6 so that DirectAccess clients have globally routable
addresses. For organizations that are already using a native IPv6 infrastructure, DirectAccess
seamlessly extends the existing infrastructure to DirectAccess client computers, and those client
computers can still access Internet resources using IPv4.
For organizations that have not yet begun deploying IPv6, DirectAccess provides a
straightforward way to begin IPv6 deployment without requiring an infrastructure upgrade. You
can use the 6to4 and Teredo IPv6 transition technologies for connectivity across the IPv4 Internet
and the ISATAP IPv6 transition technology so that DirectAccess clients can access IPv6-capable
resources across your IPv4-only intranet.
Additionally, you can deploy a Network Address Translation-Protocol Translation (NAT-PT)
device so that DirectAccess client computers can access resources on your intranet that do not
yet support IPv6.
DirectAccess and Network Access Protection
To encourage computers to comply with security and health requirement policies and reduce the
risk of malware spreading, non-compliant clients can be restricted from accessing intranet
resources or communicating with compliant computers. Using Network Access Protection (NAP)
with DirectAccess, IT administrators can require DirectAccess client computers to be healthy and
comply with corporate health requirement policies. For example, client computers can obtain a
connection to the DirectAccess server only if they have recent security updates, anti-malware
definitions, and other security settings.
Using NAP in conjunction with DirectAccess requires that NAP-enabled DirectAccess clients
submit a health certificate for authentication when creating the initial connection with the
DirectAccess server. The health certificate contains the computer’s identity and proof of system
health compliance. As previously described, a NAP-enabled DirectAccess client obtains a health
certificate by submitting its health state information to an HRA that is located on the Internet. The
health certificate must be obtained prior to initiating a connection to a DirectAccess server.
By using NAP with DirectAccess, a non-compliant client computer that becomes infected with
malware cannot connect to an intranet with DirectAccess, limiting the malware’s ability to spread.
NAP is not required to use DirectAccess, but it is recommended. For more information, see
Network Access Protection on the Microsoft Web site.
DirectAccess Requirements
DirectAccess requires the following:
12

One or more DirectAccess servers running Windows Server 2008 R2 with two network
adapters: one that is connected directly to the Internet, and a second that is connected to the
intranet.

On the DirectAccess server, at least two consecutive, public IPv4 addresses assigned to the
network adapter that is connected to the Internet.

DirectAccess clients running Windows 7.

At least one domain controller and Domain Name System (DNS) server that is running
Windows Server 2008 SP2 or Windows Server 2008 R2.

A public key infrastructure (PKI) to issue computer certificates, smart card certificates, and,
for NAP, health certificates. For more information, see Public Key Infrastructure on the
Microsoft Web site.

IPsec policies to specify protection for traffic. For more information, see IPsec on the
Microsoft Web site.

IPv6 transition technologies available for use on the DirectAccess server: ISATAP, Teredo,
and 6to4.

Optionally, a non-Microsoft NAT-PT device to provide access to IPv4-only resources for
DirectAccess clients.
Summary
DirectAccess provides the following benefits:

Seamless connectivity. DirectAccess is on whenever the user has an Internet connection,
giving users access to intranet resources whether they are traveling, at the local coffee shop,
or at home.

Remote management. IT administrators can connect directly to DirectAccess client
computers to monitor them, manage them, and deploy updates, even when the user is not
logged on. This can reduce the cost of managing remote computers by keeping them up-todate with critical updates and configuration changes.

Improved security. DirectAccess uses IPsec for authentication and encryption. Optionally,
you can require smart cards for user authentication. DirectAccess integrates with NAP to
require that DirectAccess clients must be compliant with system health requirements before
allowing a connection to the DirectAccess server. IT administrators can configure the
DirectAccess server to restrict the servers that users and individual applications can access.
DirectAccess also enables users to get more out of other Windows 7 networking improvements,
such as:

Federated Search. With Federated Search, desktop searches can include files and Web
pages on your intranet whenever the user is connected to your intranet. Because
DirectAccess connects users to the intranet when then connect to the Internet, Federated
Search works automatically any time the user has an Internet connection.
13

Folder Redirection. With Folder Redirection, folders can automatically synchronize between
multiple computers across the network. If you enable DirectAccess, users with both mobile
and desktop computers can stay synchronized automatically whenever they connect to the
Internet.

Replaceable computer scenario. In this scenario, a user’s applications, documents, and
settings are stored on the network and available from any computer. If a computer is lost or
corrupted, the replacement computer does not require user-specific configuration.
With DirectAccess, client computers are always connected, better protected, and easier to
manage.
References
Active Directory
http://go.microsoft.com/fwlink/?LinkID=147288
DirectAccess
http://go.microsoft.com/fwlink/?LinkId=147011
DNS
http://go.microsoft.com/fwlink/?LinkId=147013
Group Policy
http://go.microsoft.com/fwlink/?LinkId=100760
IPv6
http://go.microsoft.com/fwlink/?LinkId=17074
IPsec
http://go.microsoft.com/fwlink/?LinkId=50170
NAP
http://go.microsoft.com/fwlink/?LinkId=56443
PKI
http://go.microsoft.com/fwlink/?LinkId=83694
14
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement