The suboptions are Agent Circuit ID and Agent Remote ID.
The DHCP relay agents can add the Agent Circuit ID to terminate switched or permanent circuits. The Agent Circuit ID encodes an agent-local identifier of the circuit from which a DHCP client-to-server packet was received. Agents can use the Circuit ID to relay DHCP responses back to the proper circuit. In the switch, the Agent Circuit ID field contains the ifIndex of the interface on which the packet is received.
DHCP relay agents can add the Agent Remote ID to terminate switched or permanent circuits, and can identify the remote host end of the circuit. The switch uses the Agent Remote ID field to encode the MAC address of the interface on which the packet is received. The Agent Remote ID must be globally unique.