Relay agent option (option 82), Figure 19 – H3C Technologies H3C S12500 Series Switches User Manual
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contained in the sub-option. The server IP addresses filed contains the IP addresses of the PXE
servers.
Figure 19 PXE server address sub-option value field
Relay agent option (Option 82)
Option 82 is the relay agent option in the option field of the DHCP message. It records the location
information about the DHCP client. When a DHCP relay agent or DHCP snooping switch receives a
client's request, it adds Option 82 to the request message and sends it to the server.
The administrator can locate the DHCP client to further implement security control and accounting. The
Option 82 supporting server can also use such information to define individual assignment policies of IP
address and other parameters for the clients.
Option 82 involves at most 255 sub-options. At least one sub-option must be defined. DHCP relay agent
supports two sub-options: sub-option 1 (Circuit ID) and sub-option 2 (Remote ID). A DHCP snooping
device supports three sub-options: sub-option 1 (Circuit ID), sub-option 2 (Remote ID), and sub-option 9.
Option 82 has no unified definition. Its padding formats vary with vendors.
There are two methods for configuring Option 82:
•
User-defined method—Manually specify the content of Option 82.
•
Non-user-defined method—Pad Option 82 in the default normal or verbose format, private format,
or standard format.
If you choose the second method, you can specify the code type for the sub-options as ASCII or HEX.
1.
Normal padding format
The padding contents for sub-options in the normal padding format are as follows:
{
Sub-option 1—Contains the VLAN ID and interface number of the interface that received the
client's request. The value of the sub-option type is 1, and that of the circuit ID type is 0.
Figure 20 Sub-option 1 in normal padding format
{
Sub-option 2—Contains the MAC address of the DHCP relay agent interface or the MAC
address of the DHCP snooping switch that received the client's request. The value of the
sub-option type is 2, and that of the remote ID type is 0.