H3C MSR 2600 Configuration Manual page 46

Through Option 43, the DHCP client can obtain the PXE server address, which is used to obtain the boot
file or other control information from the PXE server.
1. Format of Option 43:
Figure 14 Option 43 format
Network configuration parameters are carried in different sub-options of Option 43 as shown
in Figure
Sub-option type—The field value can be 0x02 (service provider identifier sub-option) or 0x80
(PXE server address sub-option).
Sub-option length—Excludes the sub-option type and sub-option length fields.
Sub-option value—The value format varies with sub-options.
2. Sub-option value field formats:
Service provider identifier sub-option value field—Contains the service provider identifier.
PXE server address sub-option value field—Contains the PXE server type that can only be 0, the
server number that indicates the number of PXE servers contained in the sub-option and server
IP addresses, as shown in
Figure 15 PXE server address sub-option value field
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
message 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 contain 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 standard definition. Its padding formats vary with vendors.
Circuit ID has the following padding formats:
String padding format—Contains a character string specified by the user.
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14.
Figure 15.
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