Installing and Administering Internet Services

Chapter 6 201
DHCP
Configuration Overview
Devices Booting From Remote Servers
The third method of DHCP clients receiving IP addresses is through the
use of what is called a BOOTP Relay Agent. A BOOTP Relay Agent is a
machine on the local network which forwards boot requests from a
DHCP or BOOTP client to a configured DHCP or BOOTP server.
Figure 6-3 Relay Agent Scenario
In the drawing, suppose that Client2 broadcasts a boot request. The
server containing the booting information belongs to a remote network.
Therefore, the broadcast message is received by the local machine known
as the relay agent. The relay agent sends the message across the
gateway to the remote server, which in turns sends the boot information
for Client2 back to the relay agent. The relay agent then broadcasts a
message which is received by Client2. The message contains booting
information for Client2.
As for the gateway, the gateway could be configured to also serve as a
relay agent if the gateway is “DHCP-smart.” However, if the gateway
does not have knowledge of DHCP, then a relay agent must be used, as
shown in the drawing.
Client1 in the drawing does not need to use a relay agent because
Client1 is on the same network as the server.
Server
Client 1
Gateway
Client 2
Relay
Agent