Using Dhcp; Dhcp Relay Servers And Dhcp Servers; Figure 1: Dhcp Client/Server Model - Juniper EX3400 Features Manual

DHCP and Other System Services Feature Guide for EX2300, EX3400, and EX4300 Switches

Using DHCP

DHCP Relay Servers and DHCP Servers

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Figure 1: DHCP Client/Server Model

DHCP automates network-parameter assignment to network devices. Even in small
networks, DHCP is useful because it makes it easy to add new machines to the network.
DHCP access service minimizes the overhead required to add clients to the network by
providing a centralized, server-based setup, which means that you do not have to manually
create and maintain IP address assignments for clients. In addition, when you use DHCP
to manage a pool of IP addresses among hosts, you reduce the number of IP addresses
needed on the network. DHCP does this by leasing an IP address to a host for a limited
period of time, allowing the DHCP server to share a limited number of IP addresses. DHCP
also provides a central database of devices that are connected to the network and
eliminates duplicate resource assignments. In addition to IP addresses for clients, DHCP
provides other configuration information, particularly the IP addresses of local caching
Domain Name System (DNS) resolvers, network boot servers, or other service hosts.
Another valuable DHCP feature is automatic software download for installation of
software packages on switches. DHCP clients configured for automatic software
download receive messages as part of the DHCP message exchange process—when the
software package name in the DHCP server message is different from that of the software
package that booted the DHCP client switch, the new software is downloaded and
installed. See Upgrading Software by Using Automatic Software Download.
You can configure a switch either as a DHCP server or as a DHCP relay server, but not
both. Whereas a DHCP server replies to a client with an IP address, a DHCP relay server
relays DHCP messages to and from the configured DHCP server, even if the client and
server are on different IP networks.
Configure a switch to be a DHCP relay agent if you have locally attached hosts and a
remote DHCP server.
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