Vendor-Specific Information Suboption for the Dynamic Host Configuration Protocol (DHCP) Relay Agent Option
Extracted elements (10)
Existing Remote-ID and Circuit-ID suboptions (RFC 3046) carry values tied to physical network resources such as IP addresses, ATM VCs, or DOCSIS cable-modem identifiers. The Vendor-Specific suboption was introduced to let administrators associate arbitrary additional data with relayed DHCP messages, independent of physical network configuration.
The Vendor-Specific suboption takes a form similar to the Vendor-Identifying Vendor-Specific Option (RFC 3925), using the same IANA Enterprise Number registry. Vendors using this suboption are encouraged to document their usage to enable interoperability.
A deeper defense using authentication for relay agent options via the Authentication Suboption SHOULD be deployed, in addition to perimeter defenses that block relay agent options from untrusted sources.
DHCP relay agents MAY be configured to include Vendor-Specific suboptions when they include a relay agent information option in relayed DHCP messages. The suboption types and data are assigned through mechanisms outside the scope of this memo.
Depending on the data included, the Vendor-Specific suboption may convey information identifying a specific host or user on the network. If DHCP messages travel outside the service provider's own network or suboption values become visible to other users, this may raise privacy concerns for the access or service provider.
The DHCP server, if configured to support this suboption, may use the vendor-specific information—along with other relay agent option data and client options—to assign an IP address and/or configuration parameters to the client. No special additional processing is required beyond standard relay agent option handling.
The Vendor-Specific Information Suboption (code 9) carries vendor-defined data within the DHCP relay agent information option. It contains one or more Enterprise Number / DataLen / SuboptionData tuples, allowing a single suboption instance to carry data from multiple vendors.
IANA assigned suboption number 9 to the Vendor-Specific Information Suboption from the DHCP Relay Agent Information Option suboption number space defined in RFC 3046.
Fraudulent relay agent option data could lead to theft-of-service or exhaustion of IP addresses by unauthorized clients. A host tampering with relay agent data could deny service to another host or cause the DHCP server to assign it inappropriate configuration parameters. The relay agent option depends on a trusted relationship between relay agent and server.
The suboption format is: 1-byte Code (value 9), 1-byte Length (minimum 4), followed by one or more repetitions of: 4-byte Enterprise Number (network byte order), 1-byte DataLenN, and opaque SuboptionData of DataLenN bytes. The Length field includes the first Enterprise Number.