H3C S7500E Series Ethernet Switches Operation Manual

Operation Manual – DHCP
H3C S7500E Series Ethernet Switches Chapter 3 DHCP Relay Agent Configuration
3-2
IP network
DHCP server
DHCP relay agent
DHCP client DHCP client
DHCP clientDHCP client
Figure 3-1 DHCP relay agent application
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.
Figure 3-2 DHCP relay agent work process
As shown in the figure above, the DHCP relay agent works as follows:
1) After receiving a DHCP-DISCOVER or DHCP-REQUEST broadcast message
from a DHCP client, the DHCP relay agent fills the giaddr field of the message with
its IP address and forwards the message to the designated DHCP server in
unicast mode.
2) Based on the giaddr field, the DHCP server returns an IP address and other
configuration parameters to the relay agent, which conveys them to the client.
3.1.3 DHCP Relay Agent Support for Option 82
Option 82 records the location information of the DHCP client. The administrator can
locate the DHCP client to further implement security control and accounting. For more
information, refer to
Relay agent option (Option 82).