DHCP relay agent information and option 82 insertion

DHCP relay agent information, also known as DHCP option 82, enables a DHCP relay agent to insert information about a client's identity into a DHCP client request being sent to a DHCP server. This option can be used to assist DHCP servers to implement dynamic address policy.

When DHCP snooping is enabled on the FastIron switch, DHCP option 82 is automatically enabled. DHCP packets are processed as follows:

  • Before relaying a DHCP discovery packet or DHCP request packet from a client to a DHCP server, the FastIron switch adds agent information to the packet.
  • Before relaying a DHCP reply packet from a DHCP server to a client, the FastIron switch removes relay agent information from the packet.

The DHCP relay agent (the FastIron switch) inserts DHCP option 82 attributes when relaying a DHCP request packet to a DHCP server.

Figure 13 DHCP option 82 attributes added to the DHCP packet

The FastIron switch deletes DHCP option 82 attributes before forwarding a server reply packet back to a DHCP client.

Figure 14 DHCP option 82 attributes removed from the DHCP packet

The DHCP option 82 insertion or deletion feature is available only when DHCP snooping is enabled on the client or server ports.