Users Guide

Dynamic Host Conguration Protocol (DHCP)

The Aggregator is auto-congured to operate as a dynamic host conguration protocol (DHCP) client. The DHCP server, DHCP relay

agent, and secure DHCP features are not supported. The DHCP is an application layer protocol that dynamically assigns IP addresses

and other conguration parameters to network end-stations (hosts) based on conguration policies determined by network

administrators.

DHCP relieves network administrators of manually conguring hosts, which can be a tedious and error-prone process when hosts

often join, leave, and change locations on the network and it reclaims IP addresses that are no longer in use to prevent address

exhaustion.

DHCP is based on a client-server model. A host discovers the DHCP server and requests an IP address, and the server either leases

or permanently assigns one. There are three types of devices that are involved in DHCP negotiation:

DHCP Server This is a network device oering conguration parameters to the client.

DHCP Client This is a network device requesting conguration parameters from the server.

Relay Agent This is an intermediary network device that passes DHCP messages between the client and server when the

server is not on the same subnet as the host.

NOTE: The DHCP server and relay agent features are not supported on an Aggregator.

Supported Modes

Stacking, PMUX, Standalone, VLT

Assigning an IP Address using DHCP

The following section describes DHCP and the client in a network.

When a client joins a network:

1. The client initially broadcasts a DHCPDISCOVER message on the subnet to discover available DHCP servers. This message

includes the parameters that the client requires and might include suggested values for those parameters.

2. Servers unicast or broadcast a DHCPOFFER message in response to the DHCPDISCOVER that oers to the client values for

the requested parameters. Multiple servers might respond to a single DHCPDISCOVER; the client might wait a period of time

and then act on the most preferred oer.

3. The client broadcasts a DHCPREQUEST message in response to the oer, requesting the oered values.

4. After receiving a DHCPREQUEST, the server binds the clients’ unique identier (the hardware address plus IP address) to the

accepted conguration parameters and stores the data in a database called a binding table. The server then broadcasts a

DHCPACK message, which signals to the client that it may begin using the assigned parameters.

There are additional messages that are used in case the DHCP negotiation deviates from the process previously described and

shown in the illustration below.

DHCPDECLINE

A client sends this message to the server in response to a DHCPACK if the conguration parameters are

unacceptable; for example, if the oered address is already in use. In this case, the client starts the

conguration process over by sending a DHCPDISCOVER.

Dynamic Host Conguration Protocol (DHCP)