3Com 2928 User Guide - Page 313

2 DHCP Relay Agent Configuration Introduction to DHCP Relay Agent Application Environment Since DHCP clients request IP addresses via broadcast messages, the DHCP server and clients must be on the same subnet. Therefore, a DHCP server must be available on each subnet, which is not practical. DHCP relay agent solves the problem. Via a relay agent, DHCP clients communicate with a DHCP server on another subnet to obtain configuration parameters. Thus, DHCP clients on different subnets can contact the same DHCP server, and centralized management and cost reduction are achieved. Fundamentals Figure 2-1 shows a typical application of the DHCP relay agent. Figure 2-1 DHCP relay agent application DHCP client DHCP client IP network DHCP relay agent DHCP client DHCP client DHCP server No matter whether a relay agent exists or not, the DHCP server and client interact with each other in a similar way (see section Dynamic IP Address Allocation Process). The following describes the forwarding process on the DHCP relay agent. 2-1