This article explains the scenario where the DHCP relay sends the INFORM packets to the server without adding its information to the packet.

By default, when the Relay agent receives the INFORM packet from the client, it unicasts the packet to the server, however it doesn't add its IP address into the relay agent information field. Due to this the server broadcasts the ACK packet in response to the INFORM packet. However, for other DHCP packets like DORA packets, the server's response is a unicast packet as the packets received from the relay has its IP address in the relay agent info field. However, this is not the case for INFORM packet.

In order for the relay agent to insert its IP address in the relay agent information field of INFORM packet, please include the below knob:

[edit forwarding-options dhcp-relay overrides]

user@host# set always-write-giaddr

With the help of this knob, relay agent will overwrite the giaddr of every DHCP packet with the giaddr of the DHCP relay agent before forwarding the packet to the DHCP server.

Post this the server's response to the INFORM packets will be a unicast to the relay agent.

2024-10-28 : Article Created

2024-10-28 : Article Validated