Dynamic Host Configuration Protocol (DHCP)

Dynamic Host Configuration Protocol (DHCP)
Introduction
Dynamic Host Configuration Protocol (DHCP) is a communications protocol that enables network officers to administer and automate the assignment of Internet Protocol (IP) addresses in a network. Every unit connected to the Internet needs a unique IP address. When an organization sets up its computer users with a connection to the Internet, an IP address is assigned to each computer. If you do not have DHCP, the IP address has to be entered at each computer. If you move the computers to another location in another part of the network, a new IP address must be entered. DHCP lets a network administrator supervise and distribute IP addresses from a central point. Administrators can automatically send a new IP address when a computer is plugged into a different place in the network.

Limitations
1) It is recommended that only one IP interface per port be configured to use DHCP in order to prevent a situation where two interfaces on the router obtain addresses that are on the same subnet.
2) Enabling DHCP and On Net Proxy on the same Ethernet port is not recommended.
3) The router must have a Global Address before DHCP can be operational. If the router does not have a global address configured, it cannot process DHCP replies from the server, and as a result the DHCP configuration process fails.
4) A DHCP address cannot be used as a BGP ID.
5) DHCP client is supported on ethernet ports only.

Componets
The Dynamic Host Configuration Protocol (DHCP) provides configuration parameters for Internet hosts. DHCP consists of two components:
1) A protocol for delivering host specific configuration parameters from a DHCP server to a host.
2) A mechanism for allocation of network addresses to hosts. DHCP is built on a client-server model, where designated DHCP server hosts allocate network addresses and deliver configuration parameters to dynamically configured hosts.
DHCP uses UDP as its transport protocol. DHCP messages from a client to a server are sent to the “DHCP server” (port 67), and DHCP messages from a server to a client are sent to the “DHCP client” (port 68). A server with multiple network address (such as a multi-homed host) may use any of its network addresses in
outgoing DHCP messages.

Although DHCP is not intended for use in configuring routers, routers can use DHCP to obtain some configuration parameters. Below are DHCP terms defined:

DHCP Terms Defined
BOOTP Bootstrap Protocol.
DHCP Server A host providing initialization parameters through DHCP.
DHCP Client A host requesting initialization parameters from a DHCP server.
Lease The period over which a network address is allocated to a client.


Benefits
Having DHCP client and server capability allows customers to reduce the amount of work necessary to administer any IP network. DHCP provides flexibility and allows for easy adds, moves and changes to networks that are divided into subnets on a geographical basis or on separate networks.