Relay agent option (Option 82)
Option 82 is the relay agent option. It records the location information about the DHCP client. When a DHCP relay agent or DHCP snooping device receives a client's request, it adds Option 82 to the request and sends it to the server.
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 a maximum of 255 sub-options and must include a minimum of one sub-option. Option 82 supports the following sub-options: sub-option 1 (Circuit ID), sub-option 2 (Remote ID), and sub-option 5 (Link Selection). Option 82 has no standard definition. Its padding formats vary by vendor.
Circuit ID has the following padding modes:
String padding mode—Includes a character string specified by the user.
Normal padding mode—Includes the VLAN ID and interface number of the interface that receives the client's request.
Verbose padding mode—Includes the access node identifier specified by the user, and the VLAN ID, interface number and interface type of the interface that receives the client's request.
Remote ID has the following padding modes:
String padding mode—Includes a character string specified by the user.
Normal padding mode—Includes the MAC address of the DHCP relay agent interface or the MAC address of the DHCP snooping device that receives the client's request.
Sysname padding mode—Includes the name of the device. To set the device name, use the sysname command in system view.
The Link Selection sub-option carries the IP address in the giaddr field or the IP address of a relay interface. If you use the dhcp relay source-address { ip-address | interface interface-type interface-number } command, you must enable the DHCP relay agent to support Option 82. This sub-option will then be included in Option 82.