D-Link xStack DGS-3400 Series Reference Manual page 84

x Stack
DHCP Relay Agent
Information Option 82
Check
DHCP Relay 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.
®
DGS-3400 Series Layer 2 Gigabit Ethernet M anaged Sw itch
When the DHCP server receives the packet, if the server is capable of option 82, it can
implement policies like restricting the number of IP addresses that can be assigned to a
single remote ID or circuit ID. Then the DHCP server echoes the option 82 field in the
DHCP reply. The DHCP server unicasts the reply to the back to the relay agent if the
request was relayed to the server by the relay agent. The switch verifies that it originally
inserted the option 82 data. Finally, the relay agent removes the option 82 field and
forwards the packet to the switch port that connects to the DHCP client that sent the
DHCP request.
Disabled- If the field is toggled to Disabled the relay agent will not insert and remove
DHCP relay information (option 82 field) in messages between DHCP servers and clients,
and the check and policy settings will have no effect.
This field can be toggled between Enabled and Disabled using the pull-down menu. It 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 Relay
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.
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