Incorrect DHCP packet is sent when DHCP client receives a DHCP offer on a Windows 7 SP1-based or Windows Server 2008 R2 SP1-based computer

Applies to: Windows 7 Service Pack 1Windows 7 EnterpriseWindows 7 Professional More

Symptoms


Assume that you have a Windows 7 Service Pack 1 (SP1)-based or Windows Server 2008 R2 SP1-based Dynamic Host Configuration Protocol (DHCP) client computer. The client computer has the hotfix from KB 2393659 installed. When the DHCP client receives a DHCP offer, the client sends out a DHCP offer instead of a DHCP request.

Notes
  • The expected behavior is that the DHCP client should send out a DHCP request when the DHCP client receives a DHCP offer.
  • DHCP offer should only be sent by the DHCP server.
  • When you connect the client to a third-party network device that can detect the legality of DHCP servers, the client is perceived as an unauthorized DHCP server. Therefore, the port connection to the client is blocked.
Here is a network trace sample:

58476    12:56:58 16/11/2012        DHCPSrv-1  Client             DHCP:Reply, MsgType = OFFER, TransactionID = 0xE5F0E526
58494 12:56:58 16/11/2012 0.0.0.0 255.255.255.255 DHCP:Reply, MsgType = OFFER, TransactionID = 0xE5F0E526
When the Window 7 client sends the reply offer together with source IP 0.0.0.0, the client will be blocked because it looks like an unauthorized DHCP server.

Cause


This issue occurs because DHCP clients use the same buffer for sending and receiving packets. 

Typically, when an active listener receives a duplicate offer intended for an interface that has already received its offer, the buffer that corresponds to the destination interface will be overwritten. However, the thread for that interface uses the buffer and prepares to send a request. Therefore, the sender sends an offer instead of a request.

Resolution


Hotfix information

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.

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, submit a request to 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 website: 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 be running Windows 7 SP1 or Windows Server 2008 R2 SP1.   For more information about how to obtain a Windows 7 or Windows Server 2008 R2 service pack, click the following article number to view the article in the Microsoft Knowledge Base:
976932 Information about Service Pack 1 for Windows 7 and for Windows Server 2008 R2

Registry information

To use the update in this package, you do not have to make any changes to the registry.

Restart requirement

You do not have to restart the computer after you apply this update.

Update replacement information

This update does not replace a previously released update.

Status


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

More Information


For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:
824684 Description of the standard terminology that is used to describe Microsoft software updates
For more information about this issue, click the following article number to view the article in the Microsoft Knowledge Base:
2393659 A DHCP client computer that has multiple network adapters and that is running Windows 7 or Windows Server 2008 R2 cannot renew a DHCP lease when the computer wakes

Additional file information