I’m pleased to announce that I’ve been invited to participate in this year’s TechMentor event! The event will be held at the Microsoft headquarters in Redmond, WA from August 11-15, 2014. I’ll be presenting a 3 hour deep-dive session on Windows Server 2012 R2 DirectAccess. Join me as I’ll discuss in detail how to plan, design, implement, and support DirectAccess in your environment. Topics will include infrastructure requirement gathering and preparation, network configuration, high availability and geographic redundancy, supporting Windows 7 clients, and more. Throughout the session I’ll provide valuable insight, tips and tricks, and implementation best practices to ensure that you have the highest level of success for your DirectAccess deployment. Register before June 4 to save $300.00. Hope to see you there!
All posts for the month January, 2014
Posted by Richard M. Hicks on January 30, 2014
Microsoft recently made available a hotfix to address an issue where Remote Assistance connections to remote DirectAccess clients fails. The issue occurs specifically when Windows 7 clients connect to a Windows Server 2012 DirectAccess server using the IP-HTTPS IPv6 transition protocol. In this scenario, DirectAccess clients are assigned a Unique Local IPv6 Address (ULA) using the prefix FD00::/8 for which Remote Assistance service would not listen on. If you are planning to support Windows 7 clients on your Windows Server 2012/R2 DirectAccess server and you need Remote Assistance functionality, you’ll definitely want to ensure that this hotfix is applied to all of your Windows 7 DirectAccess clients.
For more information and to download the hotfix, please refer to Microsoft Knowledge Base article KB2912883.
Posted by Richard M. Hicks on January 15, 2014
When troubleshooting name resolution issues on a Windows client, NSlookup is an essential tool. However, it is important to understand that using NSlookup on a DirectAccess client might not always work as you expect. Although using NSlookup on a DirectAccess client will work normally when the client is on the corporate network, it will not provide the correct results to queries for internal hostnames when the DirectAccess client is outside of the corporate network without taking additional steps. This is because when a DirectAccess client is outside the corporate network, the Name Resolution Policy Table (NRPT) is enabled. The NRPT provides policy-based name resolution routing for DirectAccess clients, sending name resolution requests for certain namespaces to specific DNS servers. You can view the NRPT on a Windows 8.x DirectAccess client by issuing the following PowerShell command:
You can view the NRPT on a Windows 7 DirectAccess client by issuing the following netsh command:
netsh namespace show policy
Here you’ll notice that the namespace .lab.richardhicks.net is configured to use the DNS64 service running on the DirectAccess server at 2002:62bd:d898:3333::1. Notice also that the host nls.lab.richardhicks.net is not configured to use a DNS server. This effectively exempts this host from the NRPT, forcing name resolution requests for this Fully-Qualified Domain Name (FQDN) to be delivered to the DNS servers configured on the network adapter.
A Working Example
With the NRPT enabled, which occurs whenever the DirectAccess client is outside of the corporate network, a name resolution request for app1.lab.richardhicks.net would be sent to the DNS64 service on the DirectAccess server. A name resolution request for technet.microsoft.com would be sent to the DNS servers assigned to the network adapter because the NRPT contains no entry for this namespace. And even though the host nls.lab.richardhicks.net is a part of the internal namespace, a name resolution request for this host would also be sent to the DNS servers assigned to the network adapter because it has been specifically exempted from the NRPT.
The NSlookup utility is unaware of the NRPT. Whenever you use NSlookup it will, by default, automatically send queries directly to the DNS servers configured on the network adapter, regardless of the NRPT. If you wish to use NSlookup to test name resolution for external hostnames, use it as you normally would. However, if you wish to use NSlookup to resolve internal hostnames over the DirectAccess connection, you will need to tell NSlookup to use the DNS64 service running on the DirectAccess server. You can do this by running NSlookup interactively and using the server command to point it to the IPv6 address of the DNS64 service, which you can find in the NRPT.
This also applies to the PowerShell cmdlet Resolve-DNSname. Here you’ll use the -Server switch to specify the DNS64 server’s IPv6 address.
Resolve-DNSName –Server <DNS64_IPv6_Address> app1.lab.richardhicks.net
Posted by Richard M. Hicks on January 13, 2014
Since Microsoft released security advisory KB2862152, there has been much confusion surrounding where the associated update should be installed, in what deployment scenarios it needs to be installed, and what the best way to configure it is. Recently my colleague and good friend Jason Jones and I worked together to research and answer these questions.
Microsoft security advisory KB2862152 addresses a vulnerability in IPsec that could allow an attacker to perform a man-in-the-middle attack by spoofing a DirectAccess server to intercept network traffic and potentially capture encrypted domain credentials. The associated update is designed to allow security administrators to configure DirectAccess clients to perform more rigorous validation checks when establishing the DirectAccess IPsec tunnels. It’s important to understand that without additional client-side configuration, this security update does nothing.
Windows 8 Clients
For DirectAccess deployments that use Kerberos authentication (Kerberos Proxy), the update needs to be installed on all Windows 8.x clients. No updates are required for Windows 7 clients as they are not supported using this deployment model. To enforce additional validation checks, configure the registry on the Windows 8.x DirectAccess clients with the IP addresses and Service Principal Name (SPN) of the DirectAccess server as outlined here.
Windows 7 Clients
For DirectAccess deployments that use certificate-based authentication, the update needs to be installed on all Windows 7 clients. No updates are required for Windows 8.x client using this deployment model. To enforce additional validation checks, configure the registry on the Windows 7 DirectAccess clients with the IP addresses and either the fully-qualified domain name (FQDN) of the DirectAccess server (not recommended) or the Object Identifier (OID) of the computer certificated used for IPsec authentication (recommended, with custom OID).
The choice between using FQDN or OID is a challenging one, however. Choosing to validate the DNS name is simple and straightforward, but this information may be known to an attacker, or perhaps discoverable, allowing them to spoof it. In addition, there is a limit of 10 DNS names supported using this method, which can be potentially limiting, especially in large, multi-site deployments. Using the certificate OID is even more problematic, because by default it uses a well-known Server Authentication EKU OID (22.214.171.124.126.96.36.199.1) common to many Microsoft Active Directory Certificate Services (AD CS) certificate templates which, of course, could be spoofed by an attacker even easier.
The most effective implementation of this security update for DirectAccess deployments that use certificate-based authentication is to use the OID option with a certificate configured with a custom OID. Custom OIDs are unique to your organization and will help prevent spoofing by using a unique value that is much harder to guess or determine. The remainder of this article will outline how to configure and deploy a certificate with a custom OID along with implementation details for configuring the appropriate client-side registry settings via group policy to enforce the additional validation checks.
To implement this, it will require creating and deploying a new certificate template. In the Certificate Services management console, right-click Certificate Templates and choose Manage. Right-click the Computer certificate template and choose Duplicate Template. Select the General tab and give the template a descriptive name.
Select the Extensions tab, highlight Application Policies and click Edit. Click Add and then New, and then provide a descriptive name. Leave the OID as is and click Ok to continue.
Right-click once again on Certificate Templates and choose New and then Certificate Template to Issue. Select the certificate template you just created and click Ok.
Once complete you can request a new certificate for each of your DirectAccess servers using this new template.
After you have successfully installed the computer certificate using this new template, be sure to delete the old computer certificate on each DirectAccess server. No further changes are required on the DirectAccess server.
Note: If you are assigning a computer certificate to the DirectAccess server via group policy auto enrollment, the certificate will be reinstalled again after it is deleted, once group policy refreshes. To avoid this situation you will need to deny access to this GPO to ensure that only a single computer certificate with the custom OID is installed on the DirectAccess server.
To instruct the client to validate the tunnel endpoint IPv6 address and the OID of the DirectAccess server certificate before initiating IPsec tunnels we’ll need to configure registry settings on our DirectAccess clients. Jason Jones’ article describes which settings need to be made and when, so I won’t duplicate his efforts here. However, it is recommended that you deploy these settings using group policy, which I will cover.
To create a Group Policy Object (GPO) to deploy these registry settings, open the Group Policy Management Console, expand the target domain, right-click Group Policy Objects and select New. Give the new GPO a descriptive name and click Ok. Right-click the newly created GPO and choose Edit. Expand Computer Configuration, Preferences, and Windows Settings. Right-click Registry and choose New and then Registry Item. Select Update for the action and HKEY_LOCAL_MACHINE for the hive. Enter
for the Key Path and enter DTE1 for the value. Select REG_MULTI_SZ for the Value Type and in the Value Data enter the IPv6 address of the first DTE. On the next line enter EKU:<OID> and click Ok.
Repeat this procedure for each tunnel endpoint. Finally, highlight the GPO and change the Security Filtering from Authenticated Users to the security group for your DirectAccess clients and link the GPO to the domain.
Exercise extreme caution when creating and implementing these GPOs to enforce additional validation checks. If there’s a typo somewhere or you forget a DTE, you could potentially orphan your DirectAccess clients. I recommend testing your changes by manually adding the registry entries required and then copying/pasting those settings to the GPO in Active Directory when you’re ready to deploy globally. Also, don’t forget that you’ll need to update GPOs each time you add a cluster node or multisite entry point.
Posted by Richard M. Hicks on January 7, 2014
With the rapid depletion of the global IPv4 address pool, the adoption of IPv6 is growing significantly. The total exhaustion of public IPv4 addresses is inevitable, making IPv6 knowledge an important and essential skill that network engineers and systems administrators will need to have to be successful. While there are some excellent IPv6 references available today, until now there has been a serious lack of practical, real-world implementation guidance for IPv6. Until now!
Recently my good friend Ed Horley released a book entitled Practical IPv6 for Windows Administrators. As one of the technical reviewers of this title, along with Jason Jones, I had the privilege of reading this book in advance and providing feedback as it was being developed. This new book provides detailed information for network engineers and systems administrators looking to deploy IPv6. It contains prescriptive guidance for implementing IPv6 with a focus on how the protocol affects applications and services common on many of today’s corporate networks. Topics like IPv6 address assignment and name resolution are covered in detail, along with operation and support for IPv6 with services like Exchange, SQL, SharePoint, Hyper-V, and more. In addition, PowerShell is featured prominently throughout the book.
IPv4 is a dying breed. IPv6 is the way of the future, without question. Understanding IPv6 now is critical, and it is vital that you begin obtaining knowledge and experience with the IPv6 protocol today to ensure that you won’t be left out in the cold. Start building your IPv6 skills today. Order Practical IPv6 for Windows Administrators now! Once you’ve finished reading this book, you’ll be well on your way.
Posted by Richard M. Hicks on January 2, 2014