User Datagram Protocol (UDP) traffic may not fail over to an alternate gateway. Instead, it may continue to try to connect through the first gateway. This problem may occur if your Windows XP-based client is configured with two or more default gateways. When you start your computer and the first gateway is unavailable, TCP (Transmission Control Protocol) traffic correctly fails over to the alternate gateway, and connects successfully, even though UDP traffic may not.
The dead gateway detection algorithm for Windows is designed to fail the entire client over to the alternate gateway when 25 percent of TCP sessions fail over to the alternate gateway. Windows XP does not entirely switch over to the alternate gateway if there are no existing TCP sessions and only new TCP sessions are failing over.
To resolve this problem, obtain the latest service pack for Windows XP. For additional information, click the following article number to view the article in the
Microsoft Knowledge Base:
How to Obtain the Latest Windows XP Service Pack
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.
The English version of this fix should have the following file attributes or later:
Date Time Version Size File name
02-Apr-02 19:13 5.1.2600.41 310,000 Tcpip.sys
Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article. This problem was first corrected in Windows XP Service Pack 1.
For additional information about related topics, click the article numbers below
to view the articles in the Microsoft Knowledge Base:
Dead Gateway Detection in TCP/IP for Windows NT
TCP/IP Dead Gateway Detection Algorithm Updated for Windows NT
You can obtain additional information from RFC 816, "Fault Isolation and
For information about how to obtain RFCs, please see the following article in the Microsoft Knowledge Base:
How to Obtain Request for Comments Documents from the Internet
for other considerations.