IPv6 Destination Option for Conex
draft-ietf-conex-destopt-01
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (conex WG) | |
|---|---|---|---|
| Authors | Suresh Krishnan , Mirja Kühlewind , Carlos Ucendo | ||
| Last updated | 2011-10-30 (Latest revision 2011-10-24) | ||
| Stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-conex-destopt-01
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.
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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
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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
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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].
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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.
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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
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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 <TBA1> 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
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Carlos Ralli Ucendo
Telefonica
Email: ralli@tid.es
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