Microsoft KB Archive/164394

= BOOTP Service Does Not Populate ARP Cache =

Article ID: 164394

Article Last Modified on 11/1/2006

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APPLIES TO


 * Microsoft Windows NT Server 4.0 Standard Edition

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This article was previously published under Q164394



SYMPTOMS
Windows NT 4.0 Service Pack 2 (SP2) provides a new feature that allows the DHCP Service to respond to BOOTP requests as well as DHCP requests.

From RFC 1048, the BOOTP service is defined as follows:

"The Bootstrap Protocol (BOOTP) is a UDP/IP-based protocol that allows a booting host to configure itself dynamically, and more significantly, without user supervision. It provides a means to assign a host its IP address, a file from which to download a boot program from some server, that server's address, and (if present) the address of an Internet gateway."

This means that a BOOTP server should provide 2 basic functions:
 * 1) Provide IP addresses to hosts who request them, without user intervention. Additionally, the host should be provided with other relevant information, such as default gateway address, name server address, and so forth.
 * 2) Provide location of image for client to start from. This is most often a diskless workstation.

For BOOTP clients that only require an IP address from the Windows NT BOOTP server, their clients simply request an address and the Windows NT Server provides the IP address.

In the case where the host starts from an image file on a server, this is similar to how Remote Program Load (RPL) is used for remoteboot in a Microsoft networking environment.

Typical BOOTP session:
 * 1) Client sends BOOTP request
 * 2) Server sends response containing:
 * 3) * client's IP address
 * 4) * boot image filename
 * 5) * boot image servername
 * 6) * other common IP parameters (router, dns, etc)
 * 7) Client starts trivial file transfer protocol (TFTP) download of boot image file from boot image server.

In this scenario, when the boot image server is specified as the Windows NT DHCP/BOOTP server, the client is never able to download the boot image.



CAUSE
There are two issues with using Windows NT as a BOOTP server, where an Image file is required:  The download of the image file is done using TFTP. Windows NT does not include a TFTP server service. To use Windows NT DHCP/BOOTP Server with BOOTP clients who must boot from an image file (usually diskless workstations), a third-party TFTP server is required. For more information on TFTP, see the following article in the Microsoft Knowledge Base:

ARTICLE-ID: 142373

TITLE : TFTP Server Not Included With Windows NT

 There is a bug in the BOOTP function of the DHCP Service. When the BOOTP client tries to start the TFTP session with the server, the server does an address resolution protocol (ARP) query for the client's media access control address. The client does not have a full operating system or TCP/IP stack loaded at this time because it is dependent on the boot image file, therefore the client never responds to the ARP request. The BOOTP service on the Windows NT DHCP/BOOTP server should have populated the ARP cache with the client address information when it sent the BOOTP response.



STATUS
Microsoft has confirmed this to be a problem in Windows NT version 4.0 Service Pack 2. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

Additional query words: bootp arp tftp

Keywords: kbbug kbnetwork KB164394

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