"Packet Filtering Not Enabled" Error on SBS with Proxy Server Installed (224536)

SYMPTOMS

Microsoft Proxy Server may not recognize a second network interface card (NIC) as an external interface on a BackOffice Small Business Server (SBS) computer and the following error messages may be displayed:

Packet filtering cannot be enabled on this server because it does not have an external network interface.

-or-

An Invalid Local Host Address was specified for a packet filter.

CAUSE

This problem may occur if:

The external interface's IP address is listed in the Proxy Local Address table (LAT). Some routers are configured to use IP addresses from the 192.168.X.X address range, which by default, would be included in the Proxy LAT. The default LAT In Proxy Server uses the following address ranges:
- 10.0.0.0 - 10.255.255.255
- 172.16.0.0 - 172.32.255.255
- 192.168.0.0 - 192.168.255.255
The server is configured with only one NIC and a RAS phonebook entry has not been created.

RESOLUTION

To resolve this problem, only internal IP addresses to the Proxy server should be included in the Proxy LAT. To check the Proxy server LAT:

Click the Start button, point to Programs, point to Microsoft Proxy Server, and then click Internet Service Manager (or Microsoft Management Console if SBS 4.5 or the Windows NT Option Pack has been installed).
From the Properties of either the Web or Winsock Proxy services, click Local Address Table.

If the server is configured with only one NIC, then create a RAS phonebook entry and configure Proxy to autodial.

MORE INFORMATION

Do not remove the 10.x.x.x address range from the LAT. By default, this is required to identify the internal NIC of the SBS server to Proxy Server.