DHCP Option 82 (Information Option)

Option 82, also known as the 'DHCP relay agent information option' is one of many DHCP options.

It provides additional information about which DHCP relay agent received the client's message, on which interface, in which VLAN, etc.

DHCP relay agents can add Option 82 to messages they forward to the remote DHCP server.

With DHCP snooping enabled, by default Cisco switches will add Option 82 to DHCP messages they receive from clients, even if they switch isn't acting as a DHCP relay agent.

By default, Cisco switches will drop DHCP messages with Option 82 that are received on an untrusted port.