Microsoft KB Archive/197197

= DHCP Clients Are Unable to Get IP Addresses from a DHCP Server =

Article ID: 197197

Article Last Modified on 2/27/2007

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APPLIES TO


 * Microsoft Windows 2000 Server
 * Microsoft Windows 2000 Advanced Server
 * Microsoft Windows NT Server 4.0 Standard Edition
 * Microsoft BackOffice Small Business Server 4.0
 * Microsoft BackOffice Small Business Server 4.0a
 * Microsoft Windows NT Server 4.0 Enterprise Edition

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This article was previously published under Q197197





SYMPTOMS
Dynamic Host Configuration Protocol (DHCP) clients are unable to get IP addresses from DHCP server.



CAUSE
This behavior may be caused by one of the following scenarios:

Scenario 1
Changed IP address on DHCP server and now clients cannot get IP addresses.

Scenario 2
DHCP clients across router from DHCP server are unable to get an address from the server.

Scenario 3
Multiple DHCP servers exist on the LAN.



RESOLUTION
To resolve each possible cause, use one of these solutions:

Solution for Scenario 1
A DHCP server can only service requests for a scope whose network ID is the same as the network ID of its IP address.

Make sure that the server's IP address falls in the same IP network ID as the scope it is servicing. For example, a server with IP address in the 192.168.0.0 network cannot assign addresses from a scope like 10.0.0.0, unless superscoping is used.

For additional information, please see the following articles in the Microsoft Knowledge Base:

139904 How to Configure Your DHCP Server Scope

169140 Using DHCP to Assign IP Addresses to Secondary Networks

161571 Using DHCP "Superscopes" to Serve Multiple Logical Subnets

Solution for Scenario 2
A DHCP server can provide IP addresses to client computers spanning multiple subnets if the router that separates them can act as an RFC 1542 (BOOTP) relay agent.


 * 1) Configure a BOOTP/DHCP Relay Agent on the client segment. This can be the router itself or a Windows NT computer running the DHCP relay service.
 * 2) Configure a DHCP scope to match the network address on the other side of the router where the clients are. Make sure the subnet mask is correct. - Do not configure a default gateway on the DHCP server's NIC such that it is the same address as that of the router supporting the subnet where the clients are. - Do not include that subnet's scope in any superscope that is configured on the DHCP server's LAN segment.
 * 3) Make sure there is only one logical route between the server and the remote clients.

For additional information, please see the following article in the Microsoft Knowledge Base:

174765 How to Configure Microsoft DHCP Server for BOOTP Clients

Solution for Scenario 3
Make sure that you do not configure multiple DHCP servers on the same LAN with overlapping scopes.

In case of Small Business Server, the DHCP service will automatically stop when it detects another DHCP server on the LAN.

Additional query words: smallbiz net multinetted multihomed rogue

Keywords: kbprb KB197197

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