BOOTP Service Does Not Populate ARP Cache

• Microsoft Windows NT Server version 4.0

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."

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.

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:

Step 1. Client sends BOOTP request

Step 2. Server sends response containing:

    - client's IP address
    - boot image filename
    - boot image servername
    - other common IP parameters (router, dns, etc)

         boot image file from boot image server.

CAUSE

There are two issues with using Windows NT as a BOOTP server, where an Image file is required:

1. 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: Q142373
         TITLE     : TFTP Server Not Included With Windows NT
   
   

2. 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.