Please Whitelist This Site?

I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :)

If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads.

If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK.

Thanks for your understanding!

Sincerely, Charles Kozierok
Author and Publisher, The TCP/IP Guide


NOTE: Using software to mass-download the site degrades the server and is prohibited.
If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.

The Book is Here... and Now On Sale!

The whole site in one document for easy reference!
The TCP/IP Guide

Custom Search







Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  TCP/IP Network Configuration and Management Protocols (BOOTP, DHCP, SNMP and RMON)
           9  Host Configuration and TCP/IP Host Configuration Protocols (BOOTP and DHCP)
                9  TCP/IP Bootstrap Protocol (BOOTP)

Previous Topic/Section
BOOTP Message Format
Previous Page
Pages in Current Topic/Section
1
23
Next Page
BOOTP Relay Agents (Forwarding Agents)
Next Topic/Section

BOOTP Vendor-Specific Area and Vendor Information Extensions
(Page 1 of 3)

The creators of the Boot Protocol realized that certain types of hardware might require additional information to be passed from the server to the client in order for the client to boot up. For this reason, they put into the BOOTP field format the 64-byte Vend field, also called the Vendor-Specific Area. Including this field makes BOOTP flexible, since it allows vendors to decide for themselves how they want to use the protocol, and to tailor it to their needs.

Traditional Use of the Vendor-Specific Area

A client can use the Vend field by asking for certain types of information in the field when composing its request. The server can then respond to these requests, and may also include parameters it wants the client to have even if they were not requested. The original BOOTP protocol does not define any structure for the Vendor-Specific Area, leaving this up to each manufacturer to decide.

Obviously, there is nothing preventing a client made by one manufacturer from trying to send a request to a server made by another one. If each one is expecting the Vend field to contain something different, the results will be less than satisfactory. Thus, for the Vend field to be used properly, both devices must be speaking the same “language” when it comes to the meaning of this field. This is done by setting the first four bytes of the field to a special value. Each manufacturer chooses its own “magic number” for this four-byte subfield, which is also sometimes called a “magic cookie”.

Note: Why is it called a magic “cookie”? I’m not sure, to be honest. I have heard tale that its origin may be the cookie that Alice ate to grow or shrink in the story Alice in Wonderland. Who knows. J



Previous Topic/Section
BOOTP Message Format
Previous Page
Pages in Current Topic/Section
1
23
Next Page
BOOTP Relay Agents (Forwarding Agents)
Next Topic/Section

If you find The TCP/IP Guide useful, please consider making a small Paypal donation to help the site, using one of the buttons below. You can also donate a custom amount using the far right button (not less than $1 please, or PayPal gets most/all of your money!) In lieu of a larger donation, you may wish to consider purchasing a download license of The TCP/IP Guide. Thanks for your support!
Donate $2
Donate $5
Donate $10
Donate $20
Donate $30
Donate: $



Home - Table Of Contents - Contact Us

The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005

© Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.