D-Link xStack Reference Manual page 246

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xStack DGS-3200 Series Layer 2 Managed Gigabit Ethernet Switch Web UI Reference Guide
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, users may configure a client with the
option 82 field. In this situation, disable the information check feature so that the Switch
does not remove the option 82 field from the packet. Users may 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.
Implementation of DHCP Relay Agent Information Option 82
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.
1
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 the DHCP client packet, the port number starts from 1.
Remote ID sub-option format:
1.
2
1 byte 1 byte
1. Sub-option type
2. Length
3. Remote ID type
4. Length
5. MAC address: The Switch's system MAC address.
2. 3. 4.
6 0 4
1 byte 1 byte
2. 3. 4.
8 0 6
1 byte 1 byte
Figure 8 - 2. Circuit ID and Remote ID Sub-option Format
5. 6.
VLAN Module
2 bytes 1 byte
5.
MAC address
6 bytes
232
7.
Port
1 byte