Installing and Administering Internet Services

Chapter 6 265
Dynamic Host Configuration Protocol (DHCP)
Configuration Overview
Figure 6-5 Relay Agent Scenario
In Figure 6-5, 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 dedicated relay agent must be
used.
Client1 in the drawing does not need to use a relay agent because
Client1 is on the same network as the server.
NOTE Most modern routers are DHCP-smart. The relay capability is built into
the router, so you will not need the machine dedicated as a relay agent.
For specific details on configuring DHCP to distribute IP addresses
Server
Client 1
Gateway
Client 2
Relay
Agent