Encoding Long Options in the Dynamic Host Configuration Protocol (DHCPv4)
RFC 3396
Document | Type |
RFC - Proposed Standard
(November 2002; No errata)
Updates RFC 2131
Was draft-ietf-dhc-concat (dhc WG)
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Last updated | 2013-03-02 | ||
Stream | IETF | ||
Formats | plain text pdf html bibtex | ||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 3396 (Proposed Standard) | |
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Thomas Narten | ||
Send notices to | <rdroms@cisco.com> |
Network Working Group T. Lemon Request for Comments: 3396 Nominum, Inc. Updates: 2131 S. Cheshire Category: Standards Track Apple Computer, Inc. November 2002 Encoding Long Options in the Dynamic Host Configuration Protocol (DHCPv4) Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This document specifies the processing rules for Dynamic Host Configuration Protocol (DHCPv4) options that appear multiple times in the same message. Multiple instances of the same option are generated when an option exceeds 255 octets in size (the maximum size of a single option) or when an option needs to be split apart in order to take advantage of DHCP option overloading. When multiple instances of the same option appear in the options, file and/or sname fields in a DHCP packet, the contents of these options are concatenated together to form a single option prior to processing. 1. Introduction This document updates RFC 2131 [3] by clarifying the rules for option concatenation specified in section 4.1. It is expected that the reader will be familiar with this portion of RFC 2131. The text in section 4.1 that reads "Options may appear only once, unless otherwise specified in the options document." should be considered as deleted. The DHCP protocol [3] specifies objects called "options" that are encoded in the DHCPv4 packet to pass information between DHCP protocol agents. These options are encoded as a one-byte type code, a one-byte length, and a buffer consisting of the number of bytes specified in the length, from zero to 255. Lemon & Cheshire Standards Track [Page 1] RFC 3396 Encoding Long Options in DHCPv4 November 2002 However, in some cases it may be useful to send options that are longer than 255 bytes. RFC 2131 [3] specifies that when more than one option with a given type code appears in the DHCP packet, all such options should be concatenated together. It does not, however, specify the order in which this concatenation should occur. We specify here the ordering that MUST be used by DHCP protocol agents when sending options with more than 255 bytes. This method also MUST be used for splitting options that are shorter than 255 bytes, if for some reason the encoding agent needs to do so. DHCP protocol agents MUST use this method whenever they receive a DHCP packet containing more than one occurrence of a certain type of option. 2. Terminology DHCP Throughout this document, the acronym "DHCP" is used to refer to the Dynamic Host Configuration Protocol as specified in RFC 2131 [3] and RFC 2132 [4]. DHCPv4 We have used the term "DHCPv4" in the abstract for this document to distinguish between the DHCP protocol for IPv4 as defined in RFC 2131 and RFC 2132 and the DHCP protocol for IPv6, which, at the time that this document was written, was still under development. DHCP protocol agents This refers to any device on the network that sends or receives DHCP packets - any DHCP client, server or relay agent. The nature of these devices is not important to this specification. Encoding agent The DHCP protocol agent that is composing a DHCP packet to send. Decoding agent The DHCP protocol agent that is processing a DHCP packet it has received. Options DHCP options are collections of data with type codes that indicate how the options should be used. Options can specify information that is required for the DHCP protocol, IP stack configuration parameters for the client, information allowing the client to rendezvous with DHCP servers, and so on. Lemon & Cheshire Standards Track [Page 2] RFC 3396 Encoding Long Options in DHCPv4 November 2002 Option overload The DHCP packet format is based on the BOOTP packet format defined in RFC 951 [1]. When used by DHCP protocol agents, BOOTP packets have three fields that can contain options. These are the optional parameters field, the sname field, and the filename field. The DHCP options specification [4] defines the DHCP Overload option, which specifies which of these three fields isShow full document text