Dynamic Host Configuration Protocol: Difference between revisions

Revision as of 09:14, 29 July 2025

Revision as of 13:23, 1 August 2025

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;Manual allocation: This method is also variously called ''static DHCP allocation'', ''fixed address allocation'', ''reservation'', and ''MAC/IP address binding''. An administrator maps a unique identifier (a ''client id'' or [[MAC address]]) for each client to an IP address, which is offered to the requesting client. DHCP servers may be configured to fall back to other methods if this fails.

DHCP services are used for [[Internet Protocol version 4]] (IPv4) and [[IPv6]]. The details of the protocol for IPv4 and IPv6 differ sufficiently that they may be considered separate protocols.<ref>{{cite book |title = The DHCP Handbook |year = 2003 |isbn = 978-0-672-32327-0 |first1= Ralph |last1=Droms |first2= Ted |last2=Lemon |publisher = [[SAMS Publishing]] |page = 436 }}</ref> For the IPv6 operation, devices may alternatively use [[stateless address autoconfiguration]]. IPv6 hosts may also use [[link-local addressing]] to achieve operations restricted to the local network link.

==Operation==

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===Discovery===

The DHCP client [[Broadcasting (networking)|broadcasts]] a DHCPDISCOVER message on the network subnet using the destination address {{IPaddr|255.255.255.255}} (limited broadcast) or the specific subnet [[broadcast address]] (directed broadcast). A DHCP client may also request an IP address in the DHCPDISCOVER, which the server may take into account when selecting an address to offer.

For example, if HTYPE is set to 1, to specify that the medium used is [[Ethernet]], HLEN is set to 6 because an Ethernet address (MAC address) is 6 octets long. The CHADDR is set to the MAC address used by the client. Some options are set as well.