Forefront TMG 2010 Configuration Error Alert

On a Forefront Threat Management Gateway (TMG) 2010 firewall you may encounter a Configuration Error alert like this:

The alert description states:

“The routing table for the network adapter Internal includes IP address ranges that are not defined in the array-level network Internal, to which it is bound. As a result, packets arriving at this network adapter from the IP address ranges listed below or sent to these IP address ranges via this network adapter will be dropped as spoofed. To resolve this issue, add the missing IP address ranges to the array network.
The following IP address ranges will be dropped as spoofed:

This alert is the result of the Forefront TMG firewall’s routing table and network definition being out of sync with each other. In this example, the routing table looks like this:

However, the Forefront TMG Internal network definition looks like this:

As you can see, the Forefront TMG firewall is configured with an Internal network IP address range of However, the routing table contains additional static routes that also make the and networks reachable.

To resolve this issue, highlight the Networking node in the navigation tree, select the Networks tab in the center window, then highlight the network that corresponds to the IP address range contained in the alert. In our example the address range also belongs to the Internal network. Right-click the Internal network and choose properties, choose the Addresses tab, then remove all address ranges previously configured. Next, choose Add Adapter and choose the network adapter for this network.

Using this method the IP address range for this network is built using the routing table for the network interface. This is the preferred method for defining IP address ranges for Forefront TMG networks. Save the changes and apply the configuration.

For more information on configuring network interfaces for Forefront TMG 2010 firewalls, please refer to Jason Jones’ excellent documentation on the subject here:

Recommended Network Adapter Configuration for Forefront TMG Standard Edition Servers
Recommended Network Adapter Configuration for Forefront TMG Enterprise Edition Servers


Fonte e o titular desta informação: Richard Hicks’

Sobre Julio Vaz

15 years’ experience as an IT infrastructure consultant and Solution Architect. Accomplished IT professional recognized for excellence in the design, management, and development of complex business applications. Passion for delivering software and technology that meets the needs of the business. Proven ability to work with business users together with a strong development background make for an ideal analyst or solutions architect. I'm a results-driven IT professional on consulting for integration projects with extensive experience in the engineering, administration and support. Direct experience with customer relationships, complex problem troubleshooting, implementation, optimization, technology advisor and training deliveries. Always interested in professional growth as well as high-quality service delivery. Playing the role of solution architect and project leader focusing on migrations and deployments of Office 365 (Exchange Online, Sharepoint Online and Skype for Business) and Microsoft Azure (IaaS, PaaS, SaaS DRaaS). My main responsibilities were:-design and architecture scaling Exchange Server 2003 migration, 2007, 2010, 2013 and 2016 to Office 365 with ADFS in Microsoft Azure as IaaS; -Management of major project of Yammer and Sharepoint; -Development of strong relationship with partners and major customers.
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