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Configuring DHCP Service DHCP
User Guide 547
â– Option 82
Option 82 is called the DHCP Relay Agent Information Option. It provides additional security
and a more flexible way to allocate network addresses compared with the traditional DHCP.
When enabled, the DHCP relay agent can inform the DHCP server of some specified
information of clients by inserting an Option 82 payload to DHCP request packets before
forwarding them to the DHCP server, so that the DHCP server can distribute the IP
addresses or other parameters to clients based on the payload. In this way, Option 82
prevents DHCP client requests from untrusted sources. Besides, it allows the DHCP server
to assign IP addresses of different address pools to clients in different groups.
An Option 82 has two sub-options, namely, the Agent Circuit ID and Agent Remote ID.
The information that the two sub-options carry depends on the settings of the DHCP
relay agent, and are different among devices from different vendors. To allocate network
addresses using Option 82, you need to define the two sub-options on the DHCP relay
agent, and create a DHCP class on the DHCP server to identify the Option 82 payload.
TP-Link switches preset a default circuit ID and remote ID in TLV (Type, Length, and Value)
format. You can also configure the format to include Value only and customize the Value.
Table 1-1 and Table 1-2 show the packet formats of the Agent Circuit ID and Agent Remote
ID, respectively.
Table 1-1 Packet Formats of the Agent Circuit ID with Different Option 82 Settings
Option 82 Settings
*Type
(Hex)
*Length (Hex) *Value
*Format
Circuit ID
Customization
Normal
(TLV)
Disabled 00 04 Default circuit ID
Enabled 01 Length of the customized circuit ID Customized circuit ID
Private
(Only the
value)
Disabled - - Default circuit ID
Enabled - - Customized circuit ID
Table 1-2 Packet Formats of the Agent Remote ID with Different Option 82 Settings
Option 82 Settings
*Type
(Hex)
*Length (Hex) *Value
*Format
Remote ID
Customization
Normal
(TLV)
Disabled 00 06 Default remote ID
Enabled 01 Length of the customized remote ID Customized remote ID
Private
(Only the
value)
Disabled - - Default remote ID
Enabled - - Customized remote ID
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