HP A5120 EI Series Configuration Manual page 35

 Figure 19
PXE server type can only be 0. The server number field indicates the number of PXE servers
contained in the sub-option. The server IP addresses field contains the IP addresses of the PXE
servers.
Figure 19 Format of the value field of the PXE server address sub-option
0
PXE server type (0x0000)
Server number
Server IP addresses (variable)
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 of 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. The DHCP relay
agent 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.
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.

If you choose the second method, you can specify the code type for the sub-options as ASCII or HEX.
Normal padding format
1.
Sub-option 1: Padded with 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
0
Sub-option type (0x01)
 Sub-option 2: Padded with 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.
shows the format of the value field of the PXE server address sub-option. The value of the
7
7
Length (0x06)
VLAN ID
15
15 23
Circuit ID type (0x00)
Interface number
27
31
Length (0x04)