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1.2.1 DHCP / Introducing DHCP


1.2.1 DHCP / Introducing DHCP

 Dynamic Host Configuration Protocol (DHCP) works in a client/server mode. DHCP enables DHCP clients on an IP network to obtain their configurations from a DHCP server. Less work is involved in managing an IP network when DHCP is used. The most significant configuration option the client receives from the server is its IP address. The DHCP protocol is described in RFC 2131.
A DHCP client is included in most modern operating systems including the various Windows operating systems, Novell Netware, Sun Solaris, Linux, and MAC OS. The client requests addressing values from the network DHCP server . This server manages the allocation of the IP addresses and will answer configuration requests from clients. The DHCP server can answer requests for many subnets. DHCP is not intended for configuring routers, switches, and servers. These type of hosts need to have static IP addresses.
DHCP works by providing a process for a server to allocate IP information to clients. Clients lease the information from the server for an administratively defined period. When the lease expires the client must ask for another address, although the client is typically reassigned the same address.
Administrators typically prefer a network server to offer DHCP services because these solutions are scalable and relatively easy to manage. Cisco routers can use a Cisco IOS feature set, Easy IP, to offer an optional, full-featured DHCP server. Easy IP leases configurations for 24 hours by default. This is useful in small offices and home offices where the home user can take advantage of DHCP and NAT without having an NT or UNIX server.
Administrators set up DHCP servers to assign addresses from predefined pools. DHCP servers can also offer other information, such as DNS server addresses, WINS server addresses, and domain names. Most DHCP servers also allow the administrator to define specifically what client MAC addresses can be serviced and automatically assign them the same IP address each time.
DHCP uses User Datagram Protocol (UDP) as its transport protocol. The client sends messages to the server on port 67. The server sends messages to the client on port 68.

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