Cisco 32369 User Manual

Cisco ios dhcp server, Feature overview

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Cisco IOS DHCP Server 1

Cisco IOS DHCP Server

Feature Overview

Dynamic Host Control Protocol (DHCP) enables you to automatically assign reusable IP addresses
to DHCP clients. The Cisco IOS DHCP Server feature is a full DHCP server implementation that
assigns and manages IP addresses from specified address pools within the router to DHCP clients.
If the Cisco IOS DHCP Server cannot satisfy a DHCP request from its own database, it can forward
the request to one or more secondary DHCP servers defined by the network administrator.

Figure 1 shows the basic steps that occur when a DHCP client requests an IP address from a DHCP
server. The client, Host A, sends a DHCPDISCOVER broadcast message to locate a Cisco IOS
DHCP Server. A DHCP server offers configuration parameters (such as an IP address, a MAC
address, a domain name, and a lease for the IP address) to the client in a DHSCPOFFER unicast

Figure 1

DHCP Request for an IP Address from a DHCP Server


A DHCP client may receive offers from multiple DHCP servers and can accept any one of the

offers; however, the client usually accepts the first offer it receives. Additionally, the offer from the
DHCP server is not a guarantee that the IP address will be allocated to the client; however, the server
usually reserves the address until the client has had a chance to formally request the address.

The client returns a formal request for the offered IP address to the DHCP server in a
DHCPREQUEST broadcast message. The DHCP server confirms that the IP address has been
allocated to the client by returning a DHCPACK unicast message to the client.

Host A

DHCPACK (unicast)

DHCPREQUEST (broadcast)

DHCPOFFER (unicast)

DHCPDISCOVER (broadcast)

Cisco IOS

DHCP server


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