Principles of the DHCP option 82 feature


When a Dynamic Host Configuration Protocol (DHCP) client sends a request packet to the DHCP server through the DHCP relay, the DHCP relay adds option 82 to this packet. After receiving the DHCP request packet forwarded by the DHCP relay agent, the DHCP server records the information carried by option 82 of the packet, and then sends the packet that carries the DHCP configuration and option 82 back to the DHCP relay agent. After receiving the packet returned from the DHCP server, the DHCP relay forwards the processed packet to the client.
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Other related questions:
DHCP option 60 support
S series switches (except S1700 switches) support the Option 60 field of DHCP Request packets only when they function as DHCP clients.

Reasons why the Option 82 field in packets sent by other devices is replaced after the function of forcibly appending the Option 82 field is configured on S9700
S series switches support the Option 82 insertion function. The switch adds the configured Option 82 to received DHCP packets that do not contain the Option 82 field. If the packets received from other devices contain Option 82 fields, the switch deletes their original Option 82 fields and adds the configured Option 82 field to the packets.

Inner VLAN ID setting for user packets on S series switch when the DHCP Option 82 field contains only one VLAN ID
If the DHCP Option 82 field defined on an S series switch contains only one VLAN ID and specifies the inner VLAN ID value, the switch sets the inner VLAN ID of user packets to 4096. Different carriers process invalid VLAN IDs in the DHCP Option 82 field in different ways. On a network, if the BRAS connected to the switch has specific requirements for invalid inner VLAN IDs in the DHCP Option 82 field, configure the Option 82 format that does not contain the inner VLAN ID. To configure the Option 82 format, run the dhcp option82 format user-defined text command in the system view or interface view.

What cautions should be taken when configuring DHCP Option 60 and Option 43 on a Layer 2/Layer 3 network?
DHCP Option 43 and Option 60 must be configured on a Layer 3 network, while they are optional on a Layer 2 network.

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