Archive for August, 2011

Windows VPN Client and local DNS resolution

Posted: August 25, 2011 in Security
Tags: ,

Typically when configuring a remote access VPN, the goal is for DNS requests to be resolved by DNS servers on the remote/server side of the VPN connection.

This is either because the connection is from a less trusted network to a more trusted one – i.e. from home to office, and so split tunnels are not allowed. Even if split tunnels are allowed, the local client network is typically less complex and can use broadcast name resolution while the remote network is complex so using it requires DNS.

Since this is the predominant configuration, this is how most VPN clients are configured and many, including the Windows VPN client, do not offer an option to change this configuration.

In some cases, however, it makes sense for DNS resolution to remain local to the client side of the VPN connection. This is useful when the connection is from a more trusted and complex network to a less trusted and complex network. For example, a connection from the office network to a lab network or to a home network, would benefit from keeping DNS resolution on the client side of the connection.

I ran into this problem trying to configure a connection to my lab that would allow me to keep the connection open while working on the office network.

Unfortunately, this isn’t easy to do this with the VPN client that is included in Windows Vista/7 (The VPN client with Windows XP had an issue that resulted in a side effect with this exact configuration). While Windows does allow configuring the binding order to different interfaces using the ‘Advanced Settings’ menu option in the ‘Network Connections’ control panel, changing the binding order for ‘[Remote Access Connections]’ doesn’t seem to have any impact.

The binding order is stored in the registry in the following location: HKLM\System\CurrentControlSet\Services\Tcpip\Linkage\Bind. The list includes all the device GUIDs for network adapters and active connections in the binding priority order.

When working with the registry key, the following facts emerge:

  • Changing the order of the GUIDs in the registry does impact the binding order, including for VPN connections
  • Any changes to the key take effect immediately
  • When a VPN connection is completed, the GUID for the connection is added to the top of the bind order if it does not already exist
  • When a VPN connection is closed, the GUID entry for the connection is removed
  • If there are multiple GUID entries for the connection, only one is removed when the connection is closed

This mechanism creates the possibility of the following workaround:

  1. Examine the Bind registry key
  2. Connect to your VPN connection
  3. Check the Bind key again and copy the GUID that was added to the top of the list
  4. Paste the GUID entry at the bottom of the list 20 times
  5. Export the key and clean up the exported file to only include the bind key

The result is a key that will support the desired behavior. Every time a VPN connection is established, since the GUID is present, it will not be added. Since the GUID is at the bottom, DNS resolution will be done locally to the client. When the connection is disconnected, one GUID entry will be removed. After 20 VPN connections, the exported registry file can be used to reimport the key.

Of course, you can paste the GUID more times to reduce how often you have to reimport the key.

Also important to remember to redo this procedure if there are any changes to network adapters.

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Exchange 2010 supports automatic provisioning for new mailboxes. Unfortunately this mechanism does not extend to personal archives. As mailboxes are moved to Exchange 2010, they must be enabled for archives manually with the operator managing the size of each database and dividing the load accordingly.

The script below was created to automate this function and is intended to run automatically using a scheduled task on each CAS server.

Typically archive databases are flagged so that they do not participate in automatic provisioning for new mailboxes. The script selects the smallest archive database from the databases that are excluded from provisioning using the –IsExcludedeFromProvisioning parameter. Users are then enabled for archives using the target database.

The script also assigns one of two custom archive policies – a 180 day policy and a 360 day policy based on a group that defines users that get 360 days of retention in their mailbox. The script uses a custom attribute to overcome the issue of identifying mailboxes that are not members of the 360 day retention group.

Let me explain the issue:

PowerShell scripts often handle the ‘reverse group membership check’ issue by using a script that first assigns the common value (in this case 180 day retention) to everyone and then assigns the special value (in this case 360 day retention) to the members of a group.

The main weakness to this approach, especially for something like a retention policy is that any error with the second part of the script (say if someone renamed the group) would result in everyone getting a more restrictive retention policy and more archived items which is potentially disruptive and difficult to reverse.

My solution is to assign everyone in the org the less restrictive setting using a custom attribute field in AD once. Then adjust that custom attribute value based on the group membership and use the custom attribute value to configure the retention policy. This means that if the group is renamed or another error occurs, new members of the group might get the wrong policy but existing members would not be impacted.

Note that this can be accomplished with less effort if you deploy the Quest PowerGUI tools since the get-QADUser command does support a parameter –NotMemberOf. I didn’t use this since I was trying to create a solution that didn’t require additional software (in other words, come on Microsoft and implement this function!)

 

In addition, the script uses custom attribute 13 to identify a mailbox that shouldn’t use a personal archive. This is intended for service accounts and special purpose mailboxes.

#
#
# NAME: Maintenance.ps1
#
# AUTHOR: Guy Yardeni
#
# COMMENT: Script to run various maintenance tasks for Exchange 2010
#
#        Enable archives for mailboxes
#        Configure archive policy based on AD group
#

# Script to enable archive for any users who don’t already have one
# using the smallest archive database
#         
# Any text in Custom Attribute 13 will cause the script to skip the mailbox
#
#

# Return archive database with smallest size
$TargetDB = Get-MailboxDatabase -status | where {($_.ExchangeVersion.ExchangeBuild.Major -eq 14) -and ($_.IsExcludedFromProvisioning -eq $true)} | sort-object "DatabaseSize" | select-object -first 1

# Enable archive to relevant mailboxes to the target database
$results = Get-Mailbox | where {($_.ExchangeVersion.ExchangeBuild.Major -eq 14) -and ($_.ArchiveDatabase -eq $null) -and ($_.CustomAttribute13 -eq "")} | enable-mailbox

-archive -archivedatabase $TargetDB.Name -retentionpolicy "360 Day Default" |measure-object
 
#Write output for testing
Write-Host $results.count "mailbox(es) were enabled for archiving on database" $TargetDB.Name

# Script to set correct archiving policy
Get-Mailbox | where {($_.CustomAttribute12 -eq "")} | set-mailbox -CustomAttribute12 "180"
Get-DistributionGroupMember "Exchange Archive Users – 360 day" | Get-Mailbox | set-mailbox -CustomAttribute12 "360"
Get-Mailbox | where {($_.ExchangeVersion.ExchangeBuild.Major -eq 14) -and ($_.CustomAttribute12 -eq "180")} | set-mailbox -retentionpolicy "180 Day Default"
Get-Mailbox | where {($_.ExchangeVersion.ExchangeBuild.Major -eq 14) -and ($_.CustomAttribute12 -eq "360")} | set-mailbox -retentionpolicy "360 Day Default"

As always, comments about the code and approach are welcome!

A quick post to make a common task a little easier.

When managing move mailbox requests, it is often useful to be able to view certain statistics to ensure that progress and migration pace are as expected and that each server is playing its expected roles.

Exchange 2010 SP 1 makes that possible using the get-moverequeststatistics powershell command-let but some manipulation and formatting makes a big difference in monitoring the results.

Try this command for a friendly view of useful information about each open move request (as well as some cool tricks you can use with the format-table command):

Get-MoveRequest | Get-MoveRequestStatistics  |Sort-Object CompletionTimeStamp| ft DisplayName, @{Expression={$_.BadItemsEncountered};Label=”Errors”}, @{Expression={$_.PercentComplete};Label=”Percent”}, @{Expression={$_.TotalMailboxSize.ToString().Split(“(“)[0]};Label=”Size”}, @{Expression={$_.totalinprogressduration};label=”Time”},@{Expression={(($_.BytesTransferred/$_.TotalInProgressDuration.TotalMinutes)*60).ToString().Split(“(“)[0]};Label=”Pace/hr”}, @{Expression={$_.MRSServerName.ToString().Split(“.”)[0]};Label=”CAS”}, @{Expression={$_.SourceDatabase.ToString().Split(“\”)[0]};Label=”SourceServer”},SourceDatabase,Status,CompletionTimestamp -auto

Redirecting the output to a file on a scheduled basis also makes troubleshooting after hours mailbox moves much easier.

Part III: Redirection (virtual directory and SSL)

Typically when users want to access Outlook Web App (OWA), they are unlikely to type the correct URL: https://webmail.domain.com/owa or /exchange. In order to accommodate common URL combinations that users may enter, commonly using HTTP instead of HTTPS and omitting the virtual directory name, we can employ redirection.

To this end, there are two types of redirection:

The first redirects HTTP traffic to HTTPS and is very easy to accomplish in a TMG environment. If you refer to the previous post, you will see a configuration step for the web listener that accomplishes this function. In the ‘Connections’ tab for the listener, HTTP connections are allowed and redirected to HTTPS. Nice and easy.

The second form of redirection help redirect URLs that reference the root of the web site, i.e. https://webmail.domain.com , to the correct virtual directory. In an Exchange 2007/2010 environment, the destination should be https://webmail.domain.com/owa. If coexistence with legacy versions  (Exchange 2003) is needed, the destination will be https://webmail.domain.com/exchange.

In either case, we will use the ‘HTTP redirection’ feature of IIS 7.5 to configure the required setting using the following process on each CAS server:

  1. Open IIS Manager and navigate to the Default Web Site
  2. Open the HTTP Redirect feature and configure the following options:
  • Redirect all requests to this destination: https://webmail.domain.com/owa
  • Redirect all requests to exact destination: unchecked
  • Only redirect requests to content in this directory: checked
  • Status code: Found (302)

While those are the required settings for the web site, settings these configuration options will automatically set the same options on any sub folders and virtual directories that do not currently have redirection configured. Since we only want the redirection on the web site, we need to remove the redirection from all sub folders.

This process results in a problem: there are three directories that do need to be redirected and those are ‘/Exchange’, ‘/Exchweb’ and ‘/Public’. These three virtual directories must be redirected to ‘/owa’ in order for the OWA service to function correctly.

The problem is evident right after turning off redirection on the ‘/owa’ virtual directory using the UI – this change also disables redirection on the three folders listed above. If you re-enable redirection on any of the three, it will also re-enable redirection on ‘/owa’. This confusing and frustrating loop creates a series of unusable configurations that aren’t simple to correct.

The problem occurs because once the settings are configured using the UI, they are stored in the web.config file for the virtual directory and the four directories discussed all share a single web.config file. If the settings are configured using appcmd.exe the information is stored elsewhere (presumably in the metabase) and the problem is resolved.

The process to correct the issue is as follows:

  1. Remove the HttpRedirect section from the web.config file for /owa.
  2. Use the following commands to configure the correct settings for all folders:

cd %windir%\system32\inetsrv
appcmd set config “Default Web Site/Exchange” /section:httpredirect /enabled:true -commit:apphost
appcmd set config “Default Web Site/Exchweb” /section:httpredirect /enabled:true -commit:apphost
appcmd set config “Default Web Site/Public” /section:httpredirect /enabled:true -commit:apphost

appcmd set config “Default Web Site/owa” /section:httpredirect /enabled:false -commit:apphost

Finally, while you are configuring virtual directories on each CAS server, confirm that the authentication settings are set to Basic Authentication for all of the virtual directories – OWA, ECP, ActiveSync, and Outlook anywhere (configured on the properties of the CAS server). I recommend viewing and making changes to these settings through the Exchange Management Console or Shell.

That should be all that’s needed. The results of following the instructions in all 3 posts of this series are an Exchange 2010 system published with TMG using a single public IP address and a seamless user experience.

A big thanks and credit for various aspects of this post go to a couple of colleagues at Convergent Computing for helping discover, test and document this information. Thank you Yasu SabaLin and Aman Ayaz.

Hope this is helpful and as always please post any comments or questions

Part II: Creating the publishing rules

If you’ve read part I of this series, you’ve hopefully got your TMG standalone array up and ready to publish Exchange 2010 services. Before creating the publishing rules themselves, we need to address authentication.

Since our TMG servers are members of a workgroup in the DMZ (same applies if using an AD domain in the DMZ with no trusts to the internal AD forest), we will need to configure a method of authentication. I typically prefer the use of LDAPS since it is supported by default on AD domain controllers and is very simple to configure.

Setting up LDAPS Infrastructure

LDAPS uses a secure lookup to validate users against the AD domain. SSL is used to secure either LDAP (port 389/636) or global catalog (port 3268/3269) queries between TMG and select DCs on the internal system.

The setup steps are as follows:

  1. Configure select DCs with a certificate – any DCs that are participating in LDAPS must have a server authentication certificate. This certificate would be deployed automatically by an AD based enterprise CA.
  2. Export the trust root certificate from one of the DCs and copy the file over to each TMG server.
  3. Import the certificate into the ‘Trusted Root Certificate authorities’ folder on each TMG server.
  4. Ensure that firewalls allow traffic from the TMG servers to the selected DCs over ports 636 and 3269.

     A few tips to assist with this task:

  • If you just deployed your CA, run the command ‘certutil –pulse’ on a DC to issue the certificate.
  • Reboot the domain controller after issuing the CA to activate a listener on ports 636 (secure LDAP) and 3269 (secure global catalog).
Configure LDAPS authentication

Within the TMG console, follow these steps to configure LDAPS:

  • Right click on the ‘Web Access Policy’ node.
  • Select ‘Configure (Related)’ and then ‘RADIUS Server Settings’
  • Select the ‘LDAP Servers’ tab and click the ‘Add’ button to create an LDAP set
  • Enter a name for the LDAP set (e.g. Internal DCs), the domain name and credentials used for authentication

NOTE: this account needs minimal rights in AD and a non-expiring password

  • Make sure that ‘Use Global Catalog (GC)’ and ‘Connect LDAP servers over secure connection’ are checked.
  • Add the selected internal DCs that were used in the preparation steps.
  • Define the mask for this LDAP set using ‘domain\*’ for the expression and the created LDAP set and click OK
  • Define another mask for this LDAP set using ‘*@domain.com’ for the expression and the created LDAP set and click OK
  • Repeat the above steps for any additional domains as needed
Publish Exchange Services

Publishing the services is fairly simple by following the wizard. Here are the steps:

First, to create the listener that will be used for all of the rules:

  • Select the ‘Firewall Policy’ folder and the Toolbox tab on the right.
  • Navigate to ‘Network Objects’ and right click ‘Web Listener’ to create a new listener with the following info:
  1. Name: Exchange 2010 Listener
  2. Require SSL secured connections with clients
  3. Web Listener IP Addresses: All Networks (and Local Host)
  4. Use a single certificate for this Web Listener: select the certificate for webmail.domain.com
  5. Authentication Settings: HTML Form Authentication and LDAP (Active Directory) client authentication
  6. Enable SSO for Web sites published with this web listener with the name: domain.com
  • Open the properties of the recently created listener, select the ‘Connections’ tab and configure the following:
  1. Enable HTTP connections on port 80
  2. Redirect all traffic from HTTP to HTTPS

Next, to publish OWA:

  • Select the Firewall Policy section and from the the ‘Tasks’ tab on the right and click on ‘Publish Exchange Web Client Access’
  • Name the rule ‘Exchange 2010 OWA’
  • Select the ‘Exchange Server 2010’ version option and check ‘Outlook Web Access’
  • Accept the default selection of ‘Publish a single web site or load balancer’
  • Accept the default selection of ‘Use SSL to connect to the published server…’
  • On the ‘Internal Publishing Details’ page, enter: webmail.domain.com
  • Check ‘Use a computer name or IP address to connect to the published server and enter the CAS array FQDN
  • Enter the ‘Public Name’ of ‘webmail.domain.com’
  • On the ‘Select Web Listener’ page, select the ‘Exchange 2010 Listener’
  • Accept the default authentication delegation using ‘Basic authentication’
  • Accept the default of ‘All Authentication Users’ and complete the wizard

Edit the recently created rule, select the ‘Paths’ tab and add a new path as follows:

  • Folder: ‘/’
  • External path: same as published folder

Next, follow the same steps to create the ActiveSync publishing rule. Change only the name and select the ‘Exchange ActiveSync’ option on the ‘Select Services’ page. Adding the root folder path isn’t necessary for this rule.

Then, following same process create the Outlook Anywhere rule with an appropriate name and the ‘Outlook Anywhere (RPC/HTTPS)’ services option. Adding the root folder path isn’t necessary for this rule.

Finally, we need to create a rule for Autodiscover, since that service uses a separate URL and some different options.

  • Right click on the ‘Exchange 2010 Outlook Anywhere’ Rule and select ‘Copy’
  • Right click on the next rule down and select ‘Paste’
  • Edit the new rule and make the following changes:
  1. Name: Exchange 2010 Autodiscover
  2. Public Name: autodiscover.domain.com
  3. Users: All Users (remove Authenticated Users)
  4. Authentication delegation: No delegation, but client may authenticate directly

All the services are now published and the only thing remaining is to improve the user experience by configuring redirection to allow any URL to be entered in the browser. The third and final part of this post addresses redirection.

Part I: Introduction and Creating the array

During a recent Exchange 2010 migration project, I found that while there are many resources online to assist with publishing Exchange 2010 using TMG, none covered my scenario very well and most were missing details that were needed to make the solution work as I desired and intended.

Since I believe that this specific scenario is common, I will outline the specific details of the installation in a series of posts covering the whole process as well as a couple of sticking points that require a few extra tricks to address.

Please note that these guides are not intended as an exhaustive step-by-step manual for this process but rather as a set of tips, tricks and guidance for anyone who is already familiar with Exchange 2010 and TMG and the overall publishing process.

The environment

Exchange 2010 with Service Pack 1 is deployed using several mailbox servers in a single DAG hosting all mailboxes. The HT and CAS roles are hosted on two shared servers. The servers are load balanced across all ports. A CAS array was created (along with a DNS record) and point to the load balancing VIP.

Note: This post does not include a detailed discussion of load balancing. The information provided should apply equally well to WNLB and a hardware load balancer.

Two TMG 2010 Enterprise servers are deployed in a DMZ with a single interface to be used as reverse proxy servers only. The TMG servers are load balanced across ports 80 and 443.

The servers are all protected using a SAN certificate that includes the intended OWA/OA/EAS URL: webmail.domain.com and the Autodiscover URL autodiscover.domain.com as well as the FQDNs of the CAS/HT servers.

Deploying TMG – Installing the array

Extending the high availability options provided by Exchange 2010 to TMG is a key part of any implementation of the platform. No point in ensuring no single points of failure in the Exchange system if one of the primary access methods (OWA, ActiveSync, etc.) is a single point of failure.

TMG provides three options for high availability:

  • Manual – this option includes multiple TMG Standard edition servers that are load balanced but not aware of each other. Rules are synchronized manually across servers.
  • Partially automated – by leveraging the Enterprise edition of TMG, the servers can share an array configuration database that is stored on one server and replicated to the other. This option is known as a standalone array. A manual process is required to failover the configuration database to the other servers.
  • Fully automated – An enterprise array can be created by offloading the configuration database to another system (or ideally, multiple redundant systems). This configuration is a fully automated cluster.

I typically prefer the partially automated solution as it doesn’t require any additional systems but avoids the potential for user error and misconfiguration. Since the configuration information is loaded into memory on each TMG server, access to the database itself is only needed when making configuration changes so a manual failover is a very acceptable risk.

Preparation steps:
  • Confirm that each node can resolve the FQDN of the other node (by using DNS or hosts file)
  • Confirm that the user account you are logged on as is the same on both nodes (same name and password)
  • Confirm that both TMG servers are joined to the same workgroup
Certificate Configuration

If the servers are part of a DMZ domain, you can use an Enterprise CA to configure certificates. Since in my experience a DMZ CA is rare, this post uses self-signed certificates to authenticate TMG servers to each other

Generate the certificates using the makecert utility:

makecert -pe -n “CN=TMGArrayRootCA” -ss my -sr LocalMachine -a sha1 -sky signature -r “TMG Array Root CA”

makecert -pe -n “CN=TMG01.dmz.com” -ss my -sr LocalMachine -a sha1 -sky exchange -eku 1.3.6.1.5.5.7.3.1 -in “TMGArrayRootCA” -is MY -ir LocalMachine -sp “Microsoft RSA SChannel Cryptographic Provider” -sy 12 “TMG01.cer”

makecert -pe -n “CN=TMG02.dmz.com” -ss my -sr LocalMachine -a sha1 -sky exchange -eku 1.3.6.1.5.5.7.3.1 -in “TMGArrayRootCA” -is MY -ir LocalMachine -sp “Microsoft RSA SChannel Cryptographic Provider” -sy 12 “TMG02.cer”

Once the certificates are generated, use the Certificates MMC to export the certificates, copy them to each TMG server and install them as follows:

  • Import the TMGArrayRootCA certificate into the trusted root certificate folder
  • Import TMG01 and TMG02 into the personal certificate folder

Finally, using TMG console browse to System and select the Install Server Certificate task in the action bar on the right.

To verify the certificate installation use the Certificates MMC focused on the service account and select ISASTGCTRL as the service. The personal folder should contain the certificate the active array manager.

Array Creation
  • On node 2 <TMG02.dmz.com> open TMG console and select ‘Join Array’ from the tasks on the server node
  • Select the Standalone array and point to the IP of node 1 and enter the administrator credentials.
  • Confirm that the root CA is already installed on the server and complete the installation. This process will create the array and join the second node to it.
  • Restart all servers (array manager and the array managed)
  • After each system comes back up, open the TMG console and open the properties of the server node. In the intra-array credentials tab select the workgroup option and enter the required credentials

This completes the TMG installation and prepares the environment for publishing Exchange services, the topic of part 2 of this post.