The administrator can use Option 82 to locate the DHCP client and further implement security control and accounting. The DHCP server can use Option 82 to provide individual configuration policies for the clients.
Option 82 can include up to 255 sub-options and must have one sub-option at least. Option 82 supports two sub-options: sub-option 1 (Circuit ID) and sub-option 2 (Remote ID).
Option 82 has no unified definition. Its padding formats vary with vendors.
By default, the normal padding format is used on the device. You can specify the code type for the sub-options as ASCII or HEX. The padding contents for sub-options in the normal padding format are as follows:
•Sub-option 1—Padded with the VLAN ID and interface number of the interface that received the client's request. The following figure gives its format. The value of the sub-option type is 1, and that of the circuit ID type is 0.
Figure 270 Sub-option 1 in normal padding format
•Sub-option 2—Padded with the MAC address of the DHCP relay agent interface or the MAC address of the DHCP snooping device that received the client's request. The following figure gives its format. The value of the sub-option type is 2, and that of the remote ID type is 0.
Figure 271 Sub-option 2 in normal padding format
Protocols and standards
•RFC 2131, Dynamic Host Configuration Protocol
•RFC 2132, DHCP Options and BOOTP Vendor Extensions
•RFC 1542, Clarifications and Extensions for the Bootstrap Protocol
•RFC 3046, DHCP Relay Agent Information Option
•RFC 3442, The Classless Static Route Option for Dynamic Host Configuration Protocol (DHCP) version 4.
296
