Windows Vista cannot obtain an IP address from certain routers or from certain non-Microsoft DHCP servers

Windows Vista cannot obtain an IP address from certain routers or from certain non-Microsoft DHCP servers

Article ID : 928233
Last Review : September 6, 2007
Revision : 2.1

SYMPTOMS

Consider the following scenario:

• You connect a Windows Vista-based computer to a network.
• A router or other device that is configured as a Dynamic Host Configuration Protocol (DHCP) server is configured on the network.
• The router or the other device does not support the DHCP BROADCAST flag.

In this scenario, Windows Vista cannot obtain an IP address.

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CAUSE

This issue occurs because of a difference in design between Windows Vista and Microsoft Windows XP Service Pack 2 (SP2). Specifically, in Windows XP SP2, the BROADCAST flag in DHCP discovery packets is set to 0 (disabled). In Windows Vista, the BROADCAST flag in DHCP discovery packets is not disabled. Therefore, some routers and some non-Microsoft DHCP servers cannot process the DHCP discovery packets.

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RESOLUTION

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

322756 (/Feedback.aspx?kbNumber=322756/) How to back up and restore the registry in Windows

To resolve this issue, disable the DHCP BROADCAST flag in Windows Vista. To do this, follow these steps:

1. Click StartStart, type regedit in the Start Search box, and then click regedit in the Programs list.

User If you are prompted for an administrator password or for confirmation, type your password, or click Continue.

2. Locate and then click the following registry subkey:

HKEY_LOCAL_MACHINE SYSTEM CurrentControlSet Services Tcpip Parameters Interfaces {GUID}

In this registry path, click the (GUID) subkey that corresponds to the network adapter that is connected to the network.

3. On the Edit menu, point to New, and then click DWORD (32-bit) Value.
4. In the New Value #1 box, type DhcpConnEnableBcastFlagToggle, and then press ENTER.
5. Right-click DhcpConnEnableBcastFlagToggle, and then click Modify.
6. In the Value data box, type 1, and then click OK.
7. Close Registry Editor.

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MORE INFORMATION

If the router or the non-Microsoft DHCP server does not support the DHCP BROADCAST flag, you can set the following registry entry as follows:

HKEY_LOCAL_MACHINE SYSTEM CurrentControlSet Services Tcpip Parameters Interfaces {GUID}

Value name: DhcpConnForceBroadcastFlag
Value type: REG_DWORD
Value data: 0

Note A data value of 0 disables this registry entry. You can use this registry entry to prevent Windows Vista from using the DHCP BROADCAST flag. After you set this registry entry, Windows Vista never uses the DHCP BROADCAST flag.

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APPLIES TO
• Windows Vista Business
• Windows Vista Enterprise
• Windows Vista Home Basic
• Windows Vista Home Premium
• Windows Vista Ultimate
• Windows Vista Enterprise 64-bit Edition
• Windows Vista Home Basic 64-bit Edition
• Windows Vista Home Premium 64-bit Edition
• Windows Vista Ultimate 64-bit Edition
• Windows Vista Starter

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Keywords: 
kbnetwork_generalbroadband kbnetwork_routerissues kbexpertisebeginner kbhardware kbtshoot kbprb KB928233

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Microsoft Knowledge Base Article

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