D-Link DGS-3600 Series User Manual page 208

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, it is possible to 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 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
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
xStack DGS-3600 Series Layer 3 Gigabit Ethernet Managed Switch
option 82 information has been added to the packet it is sent on to the DHCP server. 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 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.
2. 3. 4.
6 0 4
5. 6.
VLAN Module
192
7.
Port