| Option Code | Option Name | Option Description | Data Type | Supported | Is predefined? | Grammar |
| 1 | agent.circuit-id | The circuit-id suboption encodes an agent-local identifier of the circuit from which a DHCP client-to-server packet was received. It is intended for use by agents in relaying DHCP responses back to the proper circuit. The format of this option is currently defined to be vendor-dependent, and will probably remain that way, although the current draft allows for the possibility of standardizing the format in the future. | string | 1 | 1 | string |
| 2 | remote-id | The remote-id suboption encodes information about the remote host end of a circuit. Examples of what it might contain include caller ID information, username information, remote ATM address, cable modem ID, and similar things. In principal, the meaning is not well-specified, and it should generally be assumed to be an opaque object that is administratively guaranteed to be unique to a particular remote end of a circuit. | quoted_string | 1 | 1 | string |
| 3 | agent-id | The "Agent ID" sub-option is used to convey information about the relay agent that forwarded the DHCP message. It helps in identifying the relay agent and its characteristics in the DHCP communication. Here's a basic structure for the "Agent ID" sub-option within the "Relay Agent Information" option: Code: Specific code assigned to the "Agent ID" sub-option (e.g., 1). Length: Length of the sub-option data field. Agent ID Data: Information about the relay agent. The "Agent ID" can contain various details about the relay agent, such as its hardware type, hardware address, or other identifying information. | string | 1 | 1 | string |
| 19 | relay-port | The "relay-port" suboption is particularly useful for the DHCP server to identify the specific UDP port number used by the relay agent when forwarding DHCP messages. | string | 1 | 1 | port |
| 4 | DOCSIS-device-class | The DOCSIS-device-class suboption is intended to convey information about the host endpoint, hardware, and software, that either the host operating system or the DHCP server may not otherwise be aware of (but the relay is able to distinguish). This is implemented as a 32-bit field (4 octets), each bit representing a flag describing the host in one of these ways. So far, only bit zero (being the least significant bit) is defined in RFC3256. If this bit is set to one, the host is considered a CPE Controlled Cable Modem (CCCM). All other bits are reserved. | uint32 | 1 | 1 | uint32 |
| 5 | link-selection | The link-selection suboption is provided by relay agents to inform servers what subnet the client is actually attached to. This is useful in those cases where the giaddr (where responses must be sent to the relay agent) is not on the same subnet as the client. When this option is present in a packet from a relay agent, the DHCP server will use its contents to find a subnet declared in configuration, and from here take one step further backwards to any shared-network the subnet may be defined within; the client may be given any address within that shared network, as normally appropriate. | ipv4address | 1 | 1 | ip-address |