3Com 3032 Configuration Manual page 349

Configure DHCP Relay
Figure 127 Schematic diagram of DHCP relay
DHCP client
DHCP client
The above figure is the schematic diagram of DHCP relay. Its working principle is as
follows:
After starting DHCP client, a configuration request message is broadcast and the
DHCP relay router will send the message to the designated DHCP server on the
other network after processing it properly. According to the information provided
by the client, the server sends configuration information to the client via DHCP
relay and completes the dynamic configuration of host.
DHCP relay actually realizes transparent transmission of broadcast messages, i.e.
transmitting broadcast messages of DHCP clients to DHCP servers on other
network segments. Besides, the user can also configure transparent transmission
for broadcast messages of designated protocols as required, to enable specific
protocol broadcast messages of this network segment to arrive at other network
segments. Similarly, the destinations are specified by IP auxiliary addresses. For
example, transmit TFTP and DNS protocol messages transparently to
corresponding servers.
To implement the DHCP relay, users have to configure IP auxiliary addresses to
specify the DHCP server addresses.
DHCP configuration includes:
Configure interface relay address
Configure transparent transmission forwarding protocol.
1 Configure interface relay address
To implement DHCP relay function, you need to configure IP relay address to
specify DHCP server address. For DHCP relay, IP relay address specifies DHCP
server. After configuration the broadcast messages received by this interface will
be sent to the relay address. The interface configured with IP helper address
should support broadcast mode. An interface can be configured with up to 20
relay addresses.
Perform the following task in Ethernet interface view.
Table 380 Configure interface relay address
Operation
Configure interface relay address
Delete interface relay address
By default, an interface has no IP address.
2 Configure transparent transmission forwarding protocol
Network
DHCP trunk router
Command
ip relay-address
undo ip relay-address [
ip-address ]
Configure DHCP Relay 345
DHCP server
ip-address