Figure 21-1
VLAN 10 and VLAN 20 correspond to the 10.0.0.1/16 and 20.0.0.1/16 networks respectively,
while the DHCP Server is located on the 30.0.0.1/16 network. To have a dynamic IP
management on the 10.0.0.1/16 and 20.0.0.1/16 networks through the DHCP Server at
30.0.0.2, just enable the DHCP Relay Agent on the device that functions as the gateway,
and specify the DHCP Server IP as 30.0.0.2.
21.1.3 Understanding DHCP Relay Agent
Information(option 82)
According to the definitions in RFC3046, when a relay device performs DHCP relay, the
network information of DHCP client can be indicated in detail by adding an option, so that
the server can assign users with IP addresses for different privileges. RFC3046 specifies
that the option is numbered 82, so it is also called option82. This option can be divided into
several sub-options. Currently, the sub-options in frequent use are Circuit ID and Remote ID.
Relay agent information option82: This option can be used without running other protocol
modules. During DHCP relay, the device forms option82 information according to the entity
port that receives the DHCP request and the physical address information of the device itself,
and uploads the option82 information to the server. The option is in the following format:
Figure 21-1
Agent Circuit ID
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