Microsoft KB Archive/201745

= Third-Party BOOTP Server May Respond to DHCP Client Broadcasts =

Article ID: 201745

Article Last Modified on 11/1/2006

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APPLIES TO


 * Microsoft Windows NT Server 4.0 Standard Edition
 * Microsoft Windows NT Workstation 4.0 Developer Edition

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This article was previously published under Q201745



SYMPTOMS
A Dynamic Host Configuration Protocol (DHCP) client may receive incorrect IP Address from a BOOTP server.



CAUSE
Microsoft Windows DHCP client broadcasts for a DHCP server to obtain valid IP addresses and other configuration parameters. Third-party BOOTP Service may intercept these request packets and incorrectly respond to them by mistake. Windows clients are designed to broadcast a "Discovery" message and if a program other than a DHCP server responds and takes the broadcasts "out of context", the resolution must come from the offending program performing the "Offer" message, not the client.



RESOLUTION
To resolve any of these or related issues, contact the third-party vendor or reconfigure the BOOTP service to not respond to packets of this nature.



MORE INFORMATION
DHCP is an extension of the initial Bootstrap Protocol or BOOTP, which assigned IP addresses from a database of physical addresses matching IP addresses. This database is configured by an Administrator and has a high amount of overhead. With the inception of DHCP, IP address assignment can be fully automated through several different avenues.

There are a few differences in BOOTP and DHCP. BOOTP clients can use DHCP servers and DHCP clients can make use of the BOOTP relay service. DHCP also has a DHCP Class Identifier parameter. A requesting client populates this parameter and sends it to the server. In turn, the server uses this parameter field for selecting correct parameters (options) for the client.

A server or router with a BOOTP service running should not respond to a request for which there are no reservations. In the case where dynamic BOOTP has been implemented, then reservations must be made to prevent overlap in IP addressing. If you implement a dynamic BOOTP server and a DHCP server on the same subnet, it is the equivalent of two DHCP servers on the same subnet. This can cause denial of IP addresses to clients as well as duplicate IP addresses on the network and is not recommended.

