DGS-3700-12/DGS-3700-12G Series Layer 2 Gigabit Ethernet User Manual
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NOTE: If the Switch receives a packet that contains the option-82 field from a DHCP client and the
information-checking feature is enabled, the switch drops the packet because it is invalid. However, in
some instances, you might configure a client with the option-82 field. In this situation, you should
disable the information-check feature so that the switch does not remove the option-82 field from the
packet. You can configure the action that the switch takes when it receives a packet with existing
option-82 information by configuring the DHCP Agent Information Option 82 Policy.
The Implementation of DHCP Information Option 82 on the Switch
The config dhcp_relay option_82 command configures the DHCP relay agent information option 82 setting of the
switch. The formats for the circuit ID sub-option and the remote ID sub-option are as follows:
NOTE: For the circuit ID sub-option of a standalone switch, the module field is always
zero.
Circuit ID sub-option format:
1. 2. 3. 4. 5. 6. 7.
1 6 0 4 VLAN
Module
Port
1 byte 1 byte 1 byte 1 byte 2 bytes 1 byte 1 byte
1. Sub-option type
2. Length
3. Circuit ID type
4. Length
5. VLAN: the incoming VLAN ID of DHCP client packet.
6. Module: For a standalone switch, the Module is always 0; For a stackable switch, the Module is
the Unit ID.
7. Port: The incoming port number of DHCP client packet, port number starts from 1.
Remote ID sub-option format:
1. 2. 3. 4. 5.
2 8 0 6 MAC address
1 byte 1 byte 1 byte 1 byte 6 bytes
1. Sub-option type
2. Length
3. Remote ID type
4. Length
5. MAC address: The Switch’s system MAC address.
Figure 9- 2 Circuit ID and Remote ID Sub-option Format
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