TP-Link T1600G-28PS Jetstream Smart Switches User Guide - Page 457

Configuring DHCP Service DHCP ■■ 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 *Format Circuit ID Customization *Type (Hex) *Length (Hex) *Value Normal (TLV) Disabled Enabled 00 04 Default circuit ID 01 Length of the customized circuit ID Customized circuit ID Private (Only the value) Disabled Enabled - - - - Default circuit ID Customized circuit ID Table 1-2 Packet Formats of the Agent Remote ID with Different Option 82 Settings Option 82 Settings *Format Remote ID Customization *Type (Hex) *Length (Hex) *Value Normal (TLV) Disabled Enabled 00 06 Default remote ID 01 Length of the customized remote ID Customized remote ID Private (Only the value) Disabled Enabled - - - - Default remote ID Customized remote ID User Guide 432