ISA Server 2004 blocks UDP traffic between two networks

A computer that is running Microsoft Internet Security and Acceleration (ISA) Server 2004 may block User Datagram Protocol (UDP) traffic between two networks.

Additionally, you may find entries that resemble the following in the ISA Server 2004 log files.Notes

• The Action column in the ISA Server 2004 log file marks the status of the connection.
• The Protocol column lists Unidentified IP Traffic instead of listing the name of the actual protocol.
• You may experience these symptoms for all UDP protocols. However, you typically experience them when you use UDP protocols such as Domain Name System (DNS) or NetBIOS.

This problem occurs because the ISA Server 2004 incorrectly processes the UDP requests.

Service pack information

ISA Server 2004 Enterprise Edition

To resolve this problem, obtain the latest service pack for ISA Server 2004 Enterprise Edition. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

Hotfix information

ISA Server 2004 Standard Edition

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.

Prerequisites

To apply this hotfix, you must have ISA Server 2004 Service Pack 2 (SP2) Standard Edition installed on the computer.

Restart requirement

You do not have to restart your computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace any other hotfixes.

File information

The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.

To work around this problem, create an access rule and use the All outbound traffic option that lets all UDP protocols transfer from the destination to the source network. For example, if the ISA Server blocks traffic from a virtual private network (VPN) client to a DNS server that is located in another subnet, you must configure and apply the rule to let traffic transfer from the network of the DNS server to the network of the VPN client.

For more information about how to configure protocols for an access rule, see ISA Server 2004 online Help.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section of this article.

For more information, click the following article number to view the article in the Microsoft Knowledge Base: