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 Configuration and Operation

DHCP General Operation and Client Finite State Machine 1 2 3 DHCP Lease Reallocation Process

To implement DHCP, an administrator must first set up a DHCP server and provide it with configuration parameters and policy information: IP address ranges, lease length specifications, and configuration data that DHCP hosts will need to be delivered to them. Host devices can then have their DHCP client software enabled, but nothing will happen until the client initiates communication with the server. When a DHCP client starts up for the first time, or when it has no current DHCP lease, it will be in an initial state where it doesn't have an address and needs to acquire one. It will do so by initiating the process of lease allocation.

Before I begin, some notes about this description, which also apply to subsequent topics in this section on DHCP lease communications:

• Addressing: DHCP assumes that clients will normally broadcast messages, since they don't know the address of servers when they initiate contact, but that servers will send replies back unicast to the client. This can be done even before the client has an IP address, by sending the message at the link layer. Some clients don't support this and require that messages to them be broadcast instead. The details of how messages are created and addressed are discussed in the section on DHCP messaging.
  
  
• DHCP Message Fields and Options: DHCP uses many of the same basic fields as BOOTP, but much of the extra information the protocol requires is carried in DHCP options. Obviously, some of these “options” aren't really optional, despite the name—they are needed for the basic function of DHCP. An obvious example would be the DHCP Message Type option, which is what specifies the message type itself. Again, you can find a full description of all DHCP fields and options in the section on DHCP messaging.
  
  
• DHCP Relay Agents: I have assumed that no relay agents are in use here; see the topic on DHCP/BOOTP relay agents for more on how they change the allocation process (and other processes).

DHCP General Operation and Client Finite State Machine 1 2 3 DHCP Lease Reallocation Process