Network Working Group T. Dreibholz
Internet-Draft University of Duisburg-Essen
Intended status: Standards Track January 10, 2008
Expires: July 13, 2008
An IPv4 Flowlabel Option
draft-dreibholz-ipv4-flowlabel-07.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on July 13, 2008.
Copyright Notice
Copyright (C) The IETF Trust (2008).
Dreibholz Expires July 13, 2008 [Page 1]
Internet-Draft An IPv4 Flowlabel Option January 2008
Abstract
This draft defines an IPv4 option containing a flowlabel that is
compatible to IPv6. It is required for simplified usage of IntServ
and interoperability with IPv6.
Dreibholz Expires July 13, 2008 [Page 2]
Internet-Draft An IPv4 Flowlabel Option January 2008
1. Introduction
1.1. Terminology
This document uses the following terms:
o IntServ (Integrated Services): Reservation of network resources
(bandwidth) on a per-flow basis. See [2], [4], [5], [6], [7], [8]
and [9] for details.
o Flow: An IntServ reservation between two endpoints.
o Flow Label: The Flow Label field of the IPv6 header and the IPv4
option header defined in this draft. It is used for marking a
packet to use a specific IntServ reservation. See [3] for a
detailed description.
1.2. Abbreviations
o RSVP: ReSource Reservation Protocol
o SCTP: Stream Control Transmission Protocol
o TCP: Transmission Control Protocol
o QoS: Quality of Service
o UDP: User Datagram Protocol
1.3. Conventions
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD.
SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when
they appear in this document, are to be interpreted as described in
[11].
Dreibholz Expires July 13, 2008 [Page 3]
Internet-Draft An IPv4 Flowlabel Option January 2008
2. A Flow Label Option for IPv4
2.1. Motivation
This section describes the motivation to add a flow label option to
the IPv4 protocol.
2.1.1. The Flow Label Field of IPv6
The Flow Label field of the IPv6 header (see [10] and [3]) is a 20-
bit pseudo-random number. All packets from the same source address
having the same flow label MUST contain the same destination address.
Therefore, the flow label combined with the source address is a
network- unique identification for a specific packet flow. The idea
behind the flow label is marking specific flows for IntServ. That
is, the routers on the path from source to destination keep e.g.
reservation states for the flows. The flow label provides easy
identification and utilizes efficient lookup, e.g. using a hash
function on the 3-tuple (source address, destination address, flow
label).
Using the IPv6 flow label, packets can be mapped easily to specific
flows, with the following features:
o Transport Layer Protocol Independence: Since the mapping is
directly specified in the IP header, all possible layer 4
protocols are supported, even protocols to be specified in a far
future.
o Support for Network Layer Encryption: The mapping is independent
of payload encryption (e.g. by IPsec).
o Support for Fragmentation: If fragmentation of a large IP packet
is necessary, all fragments contain the same flow label.
Therefore, fragmentation does not cause any flow-marking problem.
o Flow Sharing: By marking packets with a flow label, it is possible
to share a single flow (IntServ reservation) with several
communication associations from host A to host B. For example, a
video stream via UDP and a HTTP download via TCP could share a
single reservation. For the user, flow sharing has the advantage
that if one of its communication associations temporarily requires
lower bandwidth than expected, other associations sharing the same
flow may use the remaining bandwidth. That is, his possibly
expensive reservation is fully utilized. Flow sharing also helps
keeping the total number of reservations a router has to handle
small, reducing their CPU and memory requirements and therefore
cost.
Dreibholz Expires July 13, 2008 [Page 4]
Internet-Draft An IPv4 Flowlabel Option January 2008
o Multi-Flow Connections: One communication association can divide
up its packets to several flows, simply by marking packets with
different flow labels. This technique can be used for layered
transmission. That is, a stream (e.g. a video) is divided up into
several parts (called layers). For example, the first layer (base
layer) of a video contains a low-quality version, the second (1st
enhancement layer) the data to generate a higher-quality version,
etc.. Now, the first layer can be mapped to a high-quality
reservation (guaranteed bandwidth, low loss rate) at higher cost,
but the following layers can be mapped to lower-quality
reservations (e.g. higher loss rate) or even best effort at lower
cost. Research shows that the total transmission cost can be
highly reduced using layered transmission (see [12] for details).
2.1.2. The Limitations of IntServ via IPv4
Using IntServ with IPv4, there are several problems that can only be
solved with high management effort:
o No Transport Layer Protocol Independence: It is necessary to mark
the packets within the layer 4 protocol header. For example, the
TCP, UDP or SCTP port numbers can be used to mark flows (with
limitations, see below). But for new protocols (e.g.
experimental, new standards, proprietary), software updates for
*all* IntServ routers are necessary to recognize the packet flow!
o No Support for Network Layer Encryption: Since it is necessary to
read fields of the layer 4 protocol header, it may not be
encrypted. Therefore, e.g. the usage of IPsec is impossible.
o Support for Fragmentation: Only the first fragment of a large
packet contains the layer 4 header necessary to map the packet to
a flow. Mapping other fragments would require the hops to
remember packet identities and try to map fragments to packet
identities. Due to the management effort and memory requirements,
this is not realistic for high-bandwidth backbone routers;
especially when packet reordering must be considered.
Furthermore, load sharing or traffic distribution would be
impossible.
o No Flow Sharing: It is usually impossible for two different
communication associations to share the same flow, e.g. if TCP
flows are recognized using port numbers. This makes it necessary
to reserve an IntServ flow for each communication association.
This implies an increased number of flow states for routers to
keep and maintain. Furthermore, if one association temporarily
uses a lower bandwidth, the free bandwidth of its flow cannot
easily be borrowed to another association.
Dreibholz Expires July 13, 2008 [Page 5]
Internet-Draft An IPv4 Flowlabel Option January 2008
o No Multi-Flow Connections: To use layered transmission, e.g. a
video via UDP, the transmission of every layer would require own
port numbers. In the case of connection-oriented transmission
protocols (e.g. TCP, SCTP), every layer would even require its
own connection setup and management. Depending on the transport
protocol, the number of communication associations and the number
of flows, much more work is necessary compared to IPv6 using flow
labels.
All in all, using IntServ flows with IPv4 requires much more work
compared to IPv6, where simply the flow label can be used. It is
therefore useful to add such a field to IPv4, too. An appropriate
place to add such a field is an IPv4 option header.
2.2. Definition of the Flow Label Option
IPv4 (see [1]) already defines an option header for a 16-bit SATNET
stream identifier. Since this identifier would be incompatible to
the 20-bit IPv6 flow label, reuse of this existing option header is
inappropriate. Therefore, a new one is defined as follows.
Flow Label Option
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |0 0 0 0 0 0 0 0|0 0 0 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0|0 0 0 0| Flow Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Type: 143
o Length: 8 octets
o Flow Label: The 20-bit flow label. All definitions of [3] and
[10] for the IPv6 flow label are also valid for this field. A
value of zero denotes that no flow label is used. In this case,
the flow label option is in fact unnecessary.
The Flow Label option SHOULD be copied on fragmentation. It MUST be
the first option of the IP header and therefore MAY NOT appear more
than once per IPv4 packet. The Router Alert option SHOULD NOT be
used to mark the necessity for routers to examine the options.
Placing the Flow Label option as first option allows for easy
processing in hardware.
Dreibholz Expires July 13, 2008 [Page 6]
Internet-Draft An IPv4 Flowlabel Option January 2008
3. Translation between IPv6 and IPv4
Since the new IPv4 flow label is fully compatible to the IPv6 flow
label, the field MAY be translated in the other protocol's one during
protocol translation. That is, a router can translate an IPv6 packet
set from an IPv6-only host to an IPv4-mapped address of an IPv4-only
host and the flow label may simply be copied. The same may also be
applied in the backwards direction.
Note, that copying the flow label during protocol translation is not
mandatory. There may be IntServ reservation reasons for not copying
but setting the flow label to zero. But a router MAY NOT set the
flow label to another value than the copy or 0, since the source is
responsible to ensure that the source address combined with the flow
label is network-unique
Dreibholz Expires July 13, 2008 [Page 7]
Internet-Draft An IPv4 Flowlabel Option January 2008
4. References
4.1. References
[1] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[2] Braden, B., Clark, D., and S. Shenker, "Integrated Services in
the Internet Architecture: an Overview", RFC 1633, June 1994.
[3] Partridge, C., "Using the Flow Label Field in IPv6", RFC 1809,
June 1995.
[4] Braden, B., Zhang, L., Berson, S., Herzog, S., and S. Jamin,
"Resource ReSerVation Protocol (RSVP) -- Version 1 Functional
Specification", RFC 2205, September 1997.
[5] Mankin, A., Baker, F., Braden, B., Bradner, S., O'Dell, M.,
Romanow, A., Weinrib, A., and L. Zhang, "Resource ReSerVation
Protocol (RSVP) Version 1 Applicability Statement Some
Guidelines on Deployment", RFC 2208, September 1997.
[6] Braden, B. and L. Zhang, "Resource ReSerVation Protocol (RSVP)
-- Version 1 Message Processing Rules", RFC 2209,
September 1997.
[7] Wroclawski, J., "The Use of RSVP with IETF Integrated
Services", RFC 2210, September 1997.
[8] Wroclawski, J., "Specification of the Controlled-Load Network
Element Service", RFC 2211, September 1997.
[9] Shenker, S., Partridge, C., and R. Guerin, "Specification of
Guaranteed Quality of Service", RFC 2212, September 1997.
[10] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998.
[11] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
4.2. Informative References
[12] Dreibholz, T., "Management of Layered Variable Bitrate
Multimedia Streams Over DiffServ with A Priori Knowledge",
Masters Thesis University of Bonn, Institute for Computer
Science, February 2001.
Dreibholz Expires July 13, 2008 [Page 8]
Internet-Draft An IPv4 Flowlabel Option January 2008
Author's Address
Thomas Dreibholz
University of Duisburg-Essen, Institute for Experimental Mathematics
Ellernstrasse 29
45326 Essen, Nordrhein-Westfalen
Germany
Phone: +49-201-1837637
Fax: +49-201-1837673
Email: dreibh@exp-math.uni-essen.de
URI: http://www.exp-math.uni-essen.de/~dreibh/
Dreibholz Expires July 13, 2008 [Page 9]
Internet-Draft An IPv4 Flowlabel Option January 2008
Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
Dreibholz Expires July 13, 2008 [Page 10]