conex Working Group S. Krishnan Internet-Draft Ericsson Intended status: Standards Track M. Kuehlewind Expires: May 2, 2012 IKR University of Stuttgart C. Ucendo Telefonica October 30, 2011 IPv6 Destination Option for Conex draft-ietf-conex-destopt-01 Abstract Conex is a mechanism by which senders inform the network about the congestion encountered by packets earlier in the same flow. This document specifies an IPv6 destination option that is capable of carrying conex markings in IPv6 datagrams. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on May 2, 2012. Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of Krishnan, et al. Expires May 2, 2012 [Page 1] Internet-Draft Conex Destination Option October 2011 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions used in this document . . . . . . . . . . . . . . . 3 3. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Conex Destination Option (CDO) . . . . . . . . . . . . . . . . 4 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 8. Normative References . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6 Krishnan, et al. Expires May 2, 2012 [Page 2] Internet-Draft Conex Destination Option October 2011 1. Introduction Conex [CAM] is a mechanism by which senders inform the network about the congestion encountered by packets earlier in the same flow. This document specifies an IPv6 destination option [RFC2460] that can be used for performing conex markings in IPv6 datagrams. 2. Conventions used in this document 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]. 3. Background The Conex working group came up with a list of requirements that had to be met by any marking mechanism. It then considered several alternative mechanisms and evaluated their suitability for conex marking. There were no mechanisms found that were completely suitable, but the only mechanism that came close to meeting the requirements was IPv6 destination options. The analysis of the different alternatives can be found in [draft-krishnan-conex-ipv6]. Krishnan, et al. Expires May 2, 2012 [Page 3] Internet-Draft Conex Destination Option October 2011 4. Conex Destination Option (CDO) The Conex Destination Option (CDO) is a destination option that can be included in IPv6 datagrams that are sent by conex-aware senders in order to inform conex-aware nodes on the path about the CDO has an alignment requirement of (none). 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Type | Option Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |X|L|E|C| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Conex Destination Option Layout Option Type 8-bit identifier of the type of option. The option identifier for the conex destination option will be allocated by the IANA. Option Length 8-bit unsigned integer. The length of the option (excluding the Option Type and Option Length fields). This field MUST be set to the value 4. X Bit When this bit is set, the transport sender is using ConEx with this packet. If it is reset, the sender is not using ConEx. L Bit When this bit is set, the transport sender has experienced a loss. If it is reset, the sender has not experienced a loss. E Bit When this bit is set, the transport sender has experienced ECN-signaled congestion. If it is reset, the sender has not experienced ECN-signaled congestion. C Bit When this bit is set, the transport sender is building up congestion credit. Otherwise it is not. Krishnan, et al. Expires May 2, 2012 [Page 4] Internet-Draft Conex Destination Option October 2011 All packets of a ConEx-capable connection MUST carry the CDO. If the X bit is the zero all other three bits MUST be zero as well. If the X bit is zero that means that the connection is ConEx-capable but this packet SHOULD NOT be accounted to determine ConEx information in an audit function. This can be the case for e.g. pure control packets not carrying any user data. As an example in TCP pure ACKs are usually not ECN-capable and TCP does not have an mechanism to announce the lost of a pure ACK to the sender. Thus congestion information about the ACKs are not available at the sender. An audit function MUST be aware of this possibility and SHOULD ensure that not a large amount of data is sent as not-ConEx capable with a ConEx capable connection. If the X bit is set, all three other bit (L, E, C) MAY be set. When ever one if this bits is set, the number of bytes carried by this IP packet (incl. IP header) SHOULD be accounted when determining congestion or credit information. In IPv6 the length ca easily be calculated by the value given in the Payload Length header field (payload length + option space) plus a fixed value of 40 Bytes for the IP header itself. In principle all of these three bits (L, E, C) MAY be set in the same packet. In this case the packet size MUST be accounted more than once for each respective ConEx information counter. In practice loss and ECN marks can not occur at the same time, so there should usually be a way to signal the respective ConEx information in different packets. In many cases if congestion occurs the sender will not sent additional credit bit, but if e.g. a sender assumes losses because of an audit function or needs to maintain a certain sending rate to make an application layer service work, the occurrence of credit bits (c) in parallel to congestion exposure bit (L, E) is reasonable. If a network node extracts the ConEx information from a connection, this node is usually supposed to hold this information byte-wise, e.g. comparing the total number of bytes sent with the number of bytes sent with ConEx congestion mark (L, E) to determine the current whole path congestion level. When equally sized packets can be assumed accounting the number of packets (and comparing the total number to marked once) should deliver the same result. But a network node MUST be aware that this estimation can be quite wrong and thus is not reliable if e.g. different sized packed are send. 5. Acknowledgements The authors would like to thank Marcelo Bagnulo, Bob Briscoe, Ingemar Johansson, Joel Halpern and John Leslie for the discussions that led Krishnan, et al. Expires May 2, 2012 [Page 5] Internet-Draft Conex Destination Option October 2011 to this document. 6. Security Considerations This document does not bring up any new security issues. 7. IANA Considerations This document defines a new IPv6 destination option for carrying conex markings. IANA is requested to assign a new destination option type in the Destination Options registry maintained at http://www.iana.org/assignments/ipv6-parameters Conex Destination Option [RFCXXXX] The act bits for this option need to be 10 and the chg bit needs to be 0. 8. Normative References [CAM] Briscoe, B., "Congestion Exposure (ConEx) Concepts and Abstract Mechanism", draft-ietf-conex-abstract-mech-01 (work in progress), March 2011. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. Authors' Addresses Suresh Krishnan Ericsson 8400 Blvd Decarie Town of Mount Royal, Quebec Canada Email: suresh.krishnan@ericsson.com Mirja Kuehlewind IKR University of Stuttgart Email: mirja.kuehlewind@ikr.uni-stuttgart.de Krishnan, et al. Expires May 2, 2012 [Page 6] Internet-Draft Conex Destination Option October 2011 Carlos Ralli Ucendo Telefonica Email: ralli@tid.es Krishnan, et al. Expires May 2, 2012 [Page 7]