DHCPv4 Vendor-specific Message

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Abstract

This document requests a vendor-specific DHCPv4 message assignment. This message can be used for vendor specific and experimental purposes.

Table of Contents

1.  Introduction
2.  Terminology
3.  Vendor-specific Message
4.  Security Considerations
5.  IANA Considerations
6.  References
    6.1.  Normative References
    6.2.  Informative References
§  Author's Address

1.  Introduction

The DHCPv4 [RFC2131] (Droms, R., “Dynamic Host Configuration Protocol,” March 1997.) protocol specifies a mechanism for the assignment of addresses and configuration information to nodes. The protocol provides for 256 possible message codes, of which a small number are assigned ([DHCPv4Params] (IANA, “Dynamic Host Configuration Protocol (DHCP) and Bootstrap Protocol (BOOTP) Parameters. http://www.iana.org/assignments/bootp-dhcp-parameters,” .)). Each of the assigned message codes have specific purposes. New message codes are assigned through IETF Standards Action.

There may be a need for vendors of DHCPv4 clients, relay agents, or servers to experiment with new capabilities that require new messages to be exchanged between these elements. Thus, this document defines the format for and requests that a new message code be reserved for vendor-specific and experimental purposes.

2.  Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

3.  Vendor-specific Message

The vendor-specific message may be exchanged between clients, relay agents, and/or servers and allows multiple vendors to make use of the message for completely different and independent purposes.

Clients and servers MAY chose to support this message; those that do not, MUST discard the message. Relay agents SHOULD relay these messages as they would other DHCPv4 messages unless the relay agent understands the specific message and knows that the message was directed at it.

Applications using these messages MUST NOT assume that all DHCPv4 clients, relay agents, and servers support them and MUST use good networking practices when transmitting and retransmitting these messages. For some applications, it may be appropriate to use Vendor-Identifying Vendor Options [RFC3925] (Littlefield, J., “Vendor-Identifying Vendor Options for Dynamic Host Configuration Protocol version 4 (DHCPv4),” October 2004.) in a standard DHCPv4 exchange to negotiate whether the end-points support the vendor-specific message.

A vendor-specifc message is constructed by placing the Vendor-Specific Message number (254) into the DHCP Message Type option [RFC2132] (Alexander, S. and R. Droms, “DHCP Options and BOOTP Vendor Extensions,” March 1997.) and including the Vendor Message Option defined below. A Vendor-Specific Message that does not contain the Vendor Message Option MUST be ignored. A Vendor Message Option in a DHCPv4 message other than the Vendor-Specific Message MUST be ignored.

The format of the Vendor Message Option is shown below:

                        1 1 1 1 1 1
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  option-code  |  option-len   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |
   +       enterprise-number       +
   |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     vendor    |               |
   |    msg-type   |               |
   +-+-+-+-+-+-+-+-+               |
   /       vendor-option-data      /
   ~            ...                ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   option-code         OPTION_VENDOR_MESSAGE (TBD)

   option-len          5 plus the length of the vendor-option-data.

   enterprise-number   The vendor's 32-bit Enterprise Number as
                       registered with [EID], in network octet order.

   vendor-msg-type     The vendor's message-type. The values are
                       defined by the vendor identified in the
                       enterprise-number field and are not managed by
                       IANA.

   vendor-option-data  Vendor specific data (of length option-len
                       minus 5 octets). This is optional.

The vendor-option-data field MUST be encoded as a sequence of code/length/value fields of identical format to the DHCP options field. The option codes are defined by the vendor identified in the enterprise-number field and are not managed by IANA. Option codes 0 and 255 have no pre-defined interpretation or format. Each of the encapsulated options is formatted as follows:

                        1 1 1 1 1 1
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  subopt-code  |  subopt-len   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /        sub-option-data        /
   ~            ...                ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   subopt-code        The code for the encapsulated option.

   subopt-len         An unsigned integer giving the length of the
                      option-data field in this encapsulated option in
                      octets.

   sub-option-data    Data area for the encapsulated option.

Clients, relay agents, and/or servers supporting the Vendor Message Option MUST support [RFC3396] (Lemon, T. and S. Cheshire, “Encoding Long Options in the Dynamic Host Configuration Protocol (DHCPv4),” November 2002.).

Note: Vendor-Identifying Vendor Options [RFC3925] (Littlefield, J., “Vendor-Identifying Vendor Options for Dynamic Host Configuration Protocol version 4 (DHCPv4),” October 2004.) are not used to convey the vendor identification (enterprise-number) for the vendor-specific message as the message may contain instances of those options for other reasons.

4.  Security Considerations

The Security Considerations of [RFC2131] (Droms, R., “Dynamic Host Configuration Protocol,” March 1997.) apply.

This new message does potentially open up new avenues of attacking clients, relay agents, or servers. The exact nature of these attacks will depend on what functions and capabilities the message exposes and are thus not possible to describe in this document. Clients and servers that have no use for these messages SHOULD discard them and thus the threat is no different than before this message was assigned.

Vendors using this new message should use the DHCPv4 security mechanisms (such as [RFC3118] (Droms, R. and W. Arbaugh, “Authentication for DHCP Messages,” June 2001.) as appropriate) and carefully consider the security implications of the functions and capabilities exposed.

5.  IANA Considerations

IANA is requested to assign DHCPv4 Message type 254 to the Vendor-specific Message in the registry maintained in [DHCPv4Params] (IANA, “Dynamic Host Configuration Protocol (DHCP) and Bootstrap Protocol (BOOTP) Parameters. http://www.iana.org/assignments/bootp-dhcp-parameters,” .):

254 VENDOR-SPECIFIC

IANA is requested to assign a DHCPv4 option number to the Vendor Message Option in the registry maintained in [DHCPv4Params] (IANA, “Dynamic Host Configuration Protocol (DHCP) and Bootstrap Protocol (BOOTP) Parameters. http://www.iana.org/assignments/bootp-dhcp-parameters,” .):

TBD OPTION_VENDOR_MESSAGE

6.  References

6.1. Normative References

6.2. Informative References

Author's Address