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 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 Dynamic Host Configuration Protocol (DHCP)                      9  DHCP Messaging, Message Types and Formats

DHCP Message Format 1 2 3 4 Summary Of DHCP Options / BOOTP Vendor Information Fields

When BOOTP was first developed, its message format included a 64-byte Vend field, called the Vendor-Specific Area. The idea behind this field was to provide flexibility to the protocol. The BOOTP standard did not define any specific way of using this field. Instead, the field was left open for the creators of different types of hardware to use it to customize BOOTP to meet the needs of their clients and/or servers.

Including this sort of “undefined” field is always a good idea because it makes a protocol easily extensible. That is, allows the protocol to be easily enhanced in the future through the definition of new fields while not disturbing any existing fields. The problem with the BOOTP Vendor-Specific Area, however, is that the extensibility was in fact vendor-specific. It was useful only for special fields that were particular to a single vendor.

What was really needed was a way to define new fields for general purpose, vendor-independent parameter communication, but there was no field in the BOOTP message format that would let this happen. The solution came in the form of RFC 1048, which defined a technique called BOOTP vendor information extensions. This method redefines the vendor-specific area to allow it to carry general parameters between client and server. This idea was so successful that it largely replaced the older vendor-specific use of the Vend field.

DHCP Message Format 1 2 3 4 Summary Of DHCP Options / BOOTP Vendor Information Fields