RFC 3396 (rfc3396) - Page 3 of 9
Encoding Long Options in the Dynamic Host Configuration Protocol (DHCPv4)
Alternative Format: Original Text Document
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 is actually being used in any given DHCP message to store DHCP options. 3. Requirements Language In this document, the key words "MAY", "MUST, "MUST NOT", "OPTIONAL", "RECOMMENDED", "SHOULD", and "SHOULD NOT", are to be interpreted as described in BCP 14, RFC 2119 [2]. 4. Applicability This specification applies when a DHCP agent is encoding a packet containing options, where some of those options must be broken into parts. This need can occur for two reasons. First, it can occur because the value of an option that needs to be sent is longer than 255 bytes. In this case, the encoding agent MUST follow the algorithm specified here. It can also occur because there is not sufficient space in the current output buffer to store the option, but there is space for part of the option, and there is space in another output buffer for the rest. In this case, the encoding agent MUST either use this algorithm or not send the option at all. This specification also applies in any case where a DHCP protocol agent has received a DHCP packet that contains more than one instance of an option of a given type. In this case, the agent MUST concatenate these separate instances of the same option in the way that we specify here. This option updates the Dynamic Host Configuration Protocol [3] and DHCP Options and BOOTP vendor extensions [4] documents. However, because many currently-deployed DHCP protocol agents do not implement option concatenation, DHCP protocol agents should be careful not to transmit split options unless either it will not matter if the recipient cannot correctly reassemble the options, or it is certain that the recipient implements concatenation. Let us divide all DHCP options into two categories - those that, by definition, require implementation of the mechanisms defined in this document, and those that do not. We will refer to the former as concatenation-requiring options, and the latter as non- concatenation-requiring options. In order for an option to be a Lemon & Cheshire Standards Track
