Dynamic Host Conﬁguration Protocol
Dynamic Host Conﬁguration Protocol (DHCP) is a communications protocol enabling network administrators manage centrally and to automate the assignment of IP addresses in a network. In an IP network, each device connecting to the Internet needs a unique IP address. DHCP lets a network administrator supervise and distribute IP addresses from a central point and automatically sends a new IP address when a computer is plugged into a different place in the network.
DHCP uses the concept of a “lease” or amount of time that a given IP address will be valid for a computer. The lease time can vary depending on how long a user is likely to require the Internet connection at a particular location. It’s especially useful in education and other environments where users change frequently. Using very short leases, DHCP can dynamically reconﬁgure networks in which there are more computers than there are available IP addresses.
DHCP supports static addresses for computers containing Web servers that need a permanent IP address.
DHCP is an alternative to another network IP management protocol, Bootstrap Protocol (BOOTP). DHCP is a more advanced protocol but both conﬁguration management protocols are commonly used. Some operating systems, including Windows NT/2000, come with DHCP servers. A DHCP or BOOTP client is a program that is located in each computer so that it can be conﬁgured.
Op The message operation code. Messages can be either BOOTREQUEST or BOOTREPLY.
Htype The hardware address type.
Hlen The hardware address length.
Xid The transaction ID.
Secs The seconds elapsed since the client began the address acquisition or renewal process.
Flags The ﬂags.
Ciaddr The client IP address.
Yiaddr The “Your” (client) IP address.
Siaddr The IP address of the next server to use in bootstrap.
Giaddr The relay agent IP address used in booting via a relay agent.
Chaddr The client hardware address.
Sname Optional server host name, null terminated string.
File Boot ﬁle name, null terminated string; generic name or null in DHCPDISCOVER, fully qualiﬁed directory-path name in DHCPOFFER.
Options Optional parameters ﬁeld. See the options documents for a list of deﬁned options..!
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Sponsor Source DNS is deﬁned by IETF (http://www.ietf.org) RFC1034 and updated by 1035, 1101, 1183, 1348, 1876, 1982, 2181, 2308, 2535
Reference http://www.javvin.com/protocol/rfc1034.pdf Domain Names – Concept and Facilities