Archive
Disable Logging on System Policy Rules in Forefront TMG 2010
I’ve written a number of articles on improving system performance and logging optimization over the years. As I’ve mentioned previously, this involves the security administrator reviewing each access rule and deciding if the traffic is interesting enough to require logging. If it is not, to improve performance and reduce log pollution it is advisable to disable logging for the access rule in question.
However, when attempting to make this change to a system policy rule you will encounter the following error:
The changes cannot be saved. Error: 0xc0040334 This property cannot be modified for the predefined item. The error occurred on object <policy rule name> of class ‘Policy Rule’ in the scope of array .
Unfortunately the system policy editor provides no facility to make this change in the GUI. To work around this limitation you can use COM to disable logging on system policy rules programmatically using the following script. In this example I’ve chosen to disable logging on the Allow intra-array communication system policy rule.
Option Explicit
Dim Root, Array, Rule
Set Root = CreateObject("FPC.Root")
Set Array = Root.GetContainingArray()
Set Rule = Array.SystemPolicy.PolicyRules.Item("Allow intra-array communication")
Rule.EnableLogging = False
Rule.Save
WScript.Echo “Done!”
Set Rule = Nothing
Set Array = Nothing
Set Root = Nothing
Note: To see this change reflected in the management console, hit F5 to refresh or close and reopen the console.
If you wish to disable logging for all system policy rules, alter the script to use a For Each Next construct as follows:
Set Rules = Array.SystemPolicy.PolicyRules For Each Rule in Rules Rule.EnableLogging = False Next
WPAD Considerations for Kerberos Authentication with NLB VIP on Forefront TMG 2010
As I outlined in a recent article on ISAserver.org, Service Pack 2 (SP2) for Forefront TMG 2010 supports Kerberos authentication in load-balanced scenarios when web proxy clients are configured to use the virtual IP address (VIP) of the array. However, using Web Proxy Automatic Discovery (WPAD) with either DNS or DHCP poses a challenge for organizations that choose to take advantage of this new feature. When using WPAD, the web proxy client retrieves the automatic configuration script from the Forefront TMG firewall. The script provides the web proxy client with the IP addresses (or hostnames, if configured) of the individual array members. In this configuration, the web proxy client will send its request to one of the array members returned by function MakeProxies() and not to the VIP, as desired.
To work around this issue you can configure a separate web server to host the automatic configuration script. You can use any web server you wish, just make sure that it is highly available and don’t forget to configure the MIME type application/x-ns-proxy-autoconfig for the file extension you choose (typically .DAT or .PAC). Full details about how to do this can be found here. You can create your own Proxy Automatic Configuration (PAC) file from scratch, or you can simply retrieve the automatic configuration script from TMG, modify it to use the IP address (or preferably the hostname or FQDN) of the Forefront TMG array’s VIP, and place that on the web server for clients to retrieve. This means that the automatic configuration script will have to be updated manually, as required. This could be automated by writing a script that periodically retrieves the automatic configuration script from the Forefront TMG firewall, modifies it appropriately, and then saves it on the web server if you were really clever! Another alternative is to configure the Forefront TMG 2010 firewall to return a customized automatic configuration script. You can find details about this configuration here.
Error 0xc0040431 When Creating a Forefront TMG 2010 Enterprise Array
When attempting to join a Forefront TMG 2010 enterprise edition firewall to an Enterprise Management Server (EMS) managed array, you may encounter one of the following error messages:
The operation failed. Error: 0xc0040431 Forefront TMG Services failed to start after array join or an array disjoin. Check alerts, fix the configuration, and attempt to restart the services.
The operation failed. Error: 0xc0040410 The file cannot be imported because the enterprise management mode is 2010SP1 in the exported file and 2008-only in the stored configuration.
You may also encounter one of the following error messages when attempting to create a standalone array with two or more Forefront TMG 2010 enterprise edition firewalls:
The operation failed. Error: 0x80004002 No such interface supported
The operation failed. Error: 0xc0040410 The file cannot be imported because the enterprise management mode is in the exported file and in the stored configuration.
Any of these errors can occur when you attempt to join a pre-SP2 Forefront TMG 2010 firewall to an EMS-managed array running Forefront TMG SP2, or when you attempt to create a standalone array with one node running Forefront TMG SP2 and another node running SP1.
To resolve this issue, make certain that Forefront TMG 2010 firewalls are all at the same service pack and update level before joining an EMS-managed array or creating a standalone array. For information about determining which version of ISA or TMG is installed, refer to one of the following blog posts:
https://tmgblog.richardhicks.com/2010/10/11/how-to-determine-tmg-version/
https://tmgblog.richardhicks.com/2010/12/03/more-about-determining-tmg-version-numbers/
For a documented reference of ISA and TMG build numbers, click here.
Unable to Retrieve Data from Array Members after Enabling Kerberos Authentication with NLB on Forefront TMG 2010
Immediately after configuring Forefront TMG 2010 to support Kerberos authentication with NLB, you may encounter a scenario where the Forefront TMG management console fails to communicate with the members of the array and includes the following error message:
Unable to retrieve data from: <array_members>
In addition, an Event ID 4 from the Security-Kerberos source is recorded in the system event log:
The Kerberos client received a KRB_AP_ERR_MODIFIED error from the server tmgsvc2. The target name used was tmg3$@richardhicks.net. This indicates that the target server failed to decrypt the ticket provided by the client. This can occur when the target server principal name (SPN) is registered on an account other than the account the target service is using. Please ensure that the target SPN is registered on, and only registered on, the account used by the server. This error can also happen when the target service is using a different password for the target service account than what the Kerberos Key Distribution Center (KDC) has for the target service account. Please ensure that the service on the server and the KDC are both updated to use the current password. If the server name is not fully qualified, and the target domain (RICHARDHICKS.NET) is different from the client domain (RICHARDHICKS.NET), check if there are identically named server accounts in these two domains, or use the fully-qualified name to identify the server.
When making the changes to support Kerberos authentication in load balanced scenarios, the Forefront TMG firewall service is configured to run in the context of a domain user account. When the Forefront TMG management console was first opened, it authenticated to the array members using the Service Principal Name (SPN) registered to the machine (computer) account. As the changes are applied and the services are restarted, the array members are now running in the context of a domain user account. However, the management console continues to send a Kerberos ticket with the SPN registered to the machine account. The Forefront TMG firewall service running in the context of the domain user account cannot decrypt this Kerberos ticket and replies with a Kerberos error.
Resolution in this case is quite simple. Closing the Forefront TMG management console and opening it again will force the client to re-authenticate, this time using the correct SPN. The Kerberos event log errors are anomalous and can safely be ignored.
Installing Forefront TMG 2010 SP2 on Enterprise Arrays
July 4,2012 – Update: A script is now available on ISATools.org that will identify the exact order in which to install TMG SP2 for your environment. You can download the script here.
To successfully install Service Pack 2 (SP2) for Forefront TMG 2010, you must first install Service Pack 1 (SP1), then Software Update 1 for SP1 (SP1U1) as I indicated in a previous blog post. None of the other hotfix rollups available for Forefront TMG are required to upgrade to SP2. For Forefront TMG 2010 enterprise arrays, these updates must be installed in a specific order to eliminate potential conflicts. The proper sequence is as follows:
First, install SP1 for Forefront TMG 2010 on the…
- Enterprise Management Server (EMS)
- Reporting server in each array
- Remaining array members in each array
Next, install Software Update 1 for Forefront TMG 2010 SP1 on the…
- EMS
- Reporting server in each array
- Remaining array members in each array
Lastly, install SP2 for Forefront TMG 2010 on the…
- EMS
- Reporting server in each array
- Remaining array members in each array
For standalone arrays, treat the array manager as the EMS and follow the order outlined above. In addition, if you are adding a new array member to an existing array, install Forefront TMG 2010 and apply the updates in order before joining the array. Make certain that the new array member is at the same update level as the EMS and other array members. Also, consider slipstreaming SP2 with your installation media to save yourself some time.
Special thanks to Jim Harrison for clarification on the installation order.
Connect
Richard Hicks' Forefront TMG Blog 