D-Link xStack DES-3800 Series User Manual page 182

DHCP Agent
Information Option 82
Check
DHCP Agent
Information Option 82
Policy
Click Apply to implement any changes that have been made.
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.
The Implementation of DHCP Information Option 82 in DES-3828P/DES-3828DC
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.
1
1 byte 1 byte 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.
xStack DES-3800 Series Layer 3 Stackable Fast Ethernet Managed Switch
check and policy settings will have no effect.
This field can be toggled between Enabled and Disabled using the pull-down menu. This is
used to enable or disable the Switches ability to check the validity of the packet's option 82
field.
Enabled– When the field is toggled to Enable, the relay agent will check the validity of the
packet's option 82 field. If the switch receives a packet that contains the option-82 field from
a DHCP client, the switch drops the packet because it is invalid. In packets received from
DHCP servers, the relay agent will drop invalid messages.
Disabled- When the field is toggled to Disabled, the relay agent will not check the validity of
the packet's option 82 field.
This field can be toggled between Replace, Drop, and Keep by using the pull-down menu.
It is used to set the Switches policy for handling packets when the DHCP Agent
Information Option 82 Check is set to Disabled. The default is Replace.
Replace - The option 82 field will be replaced if the option 82 field already exists in the
packet received from the DHCP client.
Drop - The packet will be dropped if the option 82 field already exists in the packet received
from the DHCP client.
Keep - The option 82 field will be retained if the option 82 field already exists in the packet
received from the DHCP client.
3. 4. 5.
6 0 4
2 bytes
6. 7.
VLAN Module
1 byte 1 byte
166
Port