DHCP Overview, Motivation, History and Standards
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Overview of DHCP Features
The most significant changes are in the area of address allocation, which is enhanced through the support for dynamic address assignment mentioned above. Rather than using a static table that absolutely maps hardware addresses to IP addresses, a pool of IP addresses is used to dynamically allocate addresses. This allows addresses to be shared amongst many machines, as well as providing other benefits. Dynamic addressing allows IP addresses to be efficiently allocated, and even shared amongst devices. At the same time, DHCP still supports static mapping of addresses for devices where this is needed.
The overall operation and communication between clients and servers is again similar to that used by BOOTP, but with changes. The same basic request/reply protocol using UDP was retained for communicating configuration information, but additional message types were created to support DHCP's enhanced capabilities. BOOTP relay agents can be used by DHCP in a manner very similar to how they are used by BOOTP clients and server. The vendor information extensions from BOOTP were retained as well, but were formalized, renamed DHCP options, and extended to allow the transmission of much more information.
The result of all of this development effort is a widely-accepted, universal host configuration protocol for TCP/IP that retains compatibility with BOOTP while significantly extending its capabilities. Today, DHCP is found on millions of networks worldwide. It is used for everything from assigning IP addresses to multi-thousand-host corporate networks, to allowing a home Internet access router to automatically providing the correct Internet configuration information to a single user's computer.
The original DHCP specification was revised in March 1997 with the publishing of RFC 2131, also entitled Dynamic Host Configuration Protocol. This standard defined another new DHCP message type to allow active IP hosts to request additional configuration information. It also made several other small changes to the protocol. Since that time numerous other DHCP-related RFCs have been published, most of which either define new DHCP option types (other kinds of information DHCP servers can send to DHCP clients) or slightly refine the way that DHCP is used in particular applications.
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