Typical Application of the Option 82 Field
The DHCP Relay Agent Information Option (Option 82) field records the location of a DHCP client. A DHCP snooping-enabled device or a DHCP relay agent inserts the Option 82 field to a DHCP Request message to notify the DHCP server of the DHCP client location. Based on the Option 82 field, the DHCP server can properly assign an IP address and other configurations to the DHCP client, ensuring DHCP client security.
In Figure 13-5, the clients use the DHCP to obtain IP addresses. To improve network security, the administrator configures the device to control network access of clients connected to Interface1.
The DHCP server cannot detect the DHCP client location based only on the DHCP Request message. As a result, users in the same VLAN have the same rights to access network resources.
The Option 82 field records the location of a DHCP client and is encapsulated in a DHCP Request message that is sent to the DHCP server. To deploy different IP addresses or security policies for different clients, the DHCP server must support the Option 82 field and be configured with IP address assignment or security policies.