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Network Working Group H. Kennedy Request for Comments: 3252 Mimezine Category: Informational 1 April 2002 Binary Lexical Octet Ad-hoc Transport Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This document defines a reformulation of IP and two transport layer protocols (TCP and UDP) as XML applications. 1. Introduction 1.1. Overview This document describes the Binary Lexical Octet Ad-hoc Transport (BLOAT): a reformulation of a widely-deployed network-layer protocol (IP [RFC791]), and two associated transport layer protocols (TCP [RFC793] and UDP [RFC768]) as XML [XML] applications. It also describes methods for transporting BLOAT over Ethernet and IEEE 802 networks as well as encapsulating BLOAT in IP for gatewaying BLOAT across the public Internet. 1.2. Motivation The wild popularity of XML as a basis for application-level protocols such as the Blocks Extensible Exchange Protocol [RFC3080], the Simple Object Access Protocol [SOAP], and Jabber [JABBER] prompted investigation into the possibility of extending the use of XML in the protocol stack. Using XML at both the transport and network layer in addition to the application layer would provide for an amazing amount of power and flexibility while removing dependencies on proprietary and hard-to-understand binary protocols. This protocol unification would also allow applications to use a single XML parser for all aspects of their operation, eliminating developer time spent figuring out the intricacies of each new protocol, and moving the hard work of Kennedy Informational [Page 1]  RFC 3252 Binary Lexical Octet Ad-hoc Transport 1 April 2002 parsing to the XML toolset. The use of XML also mitigates concerns over "network vs. host" byte ordering which is at the root of many network application bugs. 1.3. Relation to Existing Protocols The reformulations specified in this RFC follow as closely as possible the spirit of the RFCs on which they are based, and so MAY contain elements or attributes that would not be needed in a pure reworking (e.g. length attributes, which are implicit in XML.) The layering of network and transport protocols are maintained in this RFC despite the optimizations that could be made if the line were somewhat blurred (i.e. merging TCP and IP into a single, larger element in the DTD) in order to foster future use of this protocol as a basis for reformulating other protocols (such as ICMP.) Other than the encoding, the behavioral aspects of each of the existing protocols remain unchanged. Routing, address spaces, TCP congestion control, etc. behave as specified in the extant standards. Adapting to new standards and experimental algorithm heuristics for improving performance will become much easier once the move to BLOAT has been completed. 1.4. Requirement Levels 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 BCP 14, RFC 2119 [RFC2119]. 2. IPoXML This protocol MUST be implemented to be compliant with this RFC. IPoXML is the root protocol REQUIRED for effective use of TCPoXML (section 3.) and higher-level application protocols. The DTD for this document type can be found in section 7.1. The routing of IPoXML can be easily implemented on hosts with an XML parser, as the regular structure lends itself handily to parsing and validation of the document/datagram and then processing the destination address, TTL, and checksum before sending it on to its next-hop. The reformulation of IPv4 was chosen over IPv6 [RFC2460] due to the wider deployment of IPv4 and the fact that implementing IPv6 as XML would have exceeded the 1500 byte Ethernet MTU. Kennedy Informational [Page 2]  RFC 3252 Binary Lexical Octet Ad-hoc Transport 1 April 2002 All BLOAT implementations MUST use - and specify - the UTF-8 encoding of RFC 2279 [RFC2279]. All BLOAT document/datagrams MUST be well- formed and include the XMLDecl. 2.1. IP Description A number of items have changed (for the better) from the original IP specification. Bit-masks, where present have been converted into human-readable values. IP addresses are listed in their dotted- decimal notation [RFC1123]. Length and checksum values are present as decimal integers. To calculate the length and checksum fields of the IP element, a canonicalized form of the element MUST be used. The canonical form SHALL have no whitespace (including newline characters) between elements and only one space character between attributes. There SHALL NOT be a space following the last attribute in an element. An iterative method SHOULD be used to calculate checksums, as the length field will vary based on the size of the checksum. The payload element bears special attention. Due to the character set restrictions of XML, the payload of IP datagrams (which MAY contain arbitrary data) MUST be encoded for transport. This RFC REQUIRES the contents of the payload to be encoded in the base-64 encoding of RFC 2045 [RFC2045], but removes the requirement that the encoded output MUST be wrapped on 76-character lines. Kennedy Informational [Page 3]  RFC 3252 Binary Lexical Octet Ad-hoc Transport 1 April 2002 2.2. Example Datagram The following is an example IPoXML datagram with an empty payload: <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE ip PUBLIC "-//IETF//DTD BLOAT 1.0 IP//EN" "bloat.dtd"> <ip> <header length="474"> <version value="4"/> <tos precedence="Routine" delay="Normal" throughput="Normal" relibility="Normal" reserved="0"/> <total.length value="461"/> <id value="1"/> <flags reserved="0" df="dont" mf="last"/> <offset value="0"/> <ttl value="255"/> <protocol value="6"/> <checksum value="8707"/> <source address="10.0.0.22"/> <destination address="10.0.0.1"/> <options> <end copied="0" class="0" number="0"/> </options> <padding pad="0"/> </header> <payload> </payload> </ip> 3. TCPoXML This protocol MUST be implemented to be compliant with this RFC. The DTD for this document type can be found in section 7.2. 3.1. TCP Description A number of items have changed from the original TCP specification. Bit-masks, where present have been converted into human-readable values. Length and checksum and port values are present as decimal integers. To calculate the length and checksum fields of the TCP element, a canonicalized form of the element MUST be used as in section 2.1. An iterative method SHOULD be used to calculate checksums as in section 2.1. The payload element MUST be encoded as in section 2.1. Kennedy Informational [Page 4]  RFC 3252 Binary Lexical Octet Ad-hoc Transport 1 April 2002 The TCP offset element was expanded to a maximum of 255 from 16 to allow for the increased size of the header in XML. TCPoXML datagrams encapsulated by IPoXML MAY omit the <?xml?> header as well as the <!DOCTYPE> declaration. 3.2. Example Datagram The following is an example TCPoXML datagram with an empty payload: <?xml version="1.0" encodin