H3C S3610-28P Operation Manual page 983

Operation Manual – DHCP
H3C S3610&S5510 Series Ethernet Switches
I. 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 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.
Now 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. Currently the
device supports two padding formats: normal and verbose.
1) Normal padding format
The padding contents for sub-options in the normal padding format are:
sub-option 1: Padded with the VLAN ID and number of the port 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 1-5 Sub-option 1 in normal padding format
sub-option 2: Padded with the MAC address of the interface 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 1-6 Sub-option 2 in normal padding format
2) Verbose padding format:
The padding contents for sub-options in the verbose padding format are:
sub-option 1: Padded with the user-specified access node identifier (ID of the
device that adds Option 82 in DHCP messages), and type, number, and VLAN ID
of the port that received the client's request. Its format is shown in the following
figure.
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Chapter 1 DHCP Overview