An IPv4 Flowlabel Option
draft-dreibholz-ipv4-flowlabel-38
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Author | Thomas Dreibholz | ||
| Last updated | 2023-09-27 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
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| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
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draft-dreibholz-ipv4-flowlabel-38
Network Working Group T. Dreibholz
Internet-Draft SimulaMet
Intended status: Standards Track 26 September 2023
Expires: 29 March 2024
An IPv4 Flowlabel Option
draft-dreibholz-ipv4-flowlabel-38
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.
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
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This Internet-Draft will expire on 29 March 2024.
Copyright Notice
Copyright (c) 2023 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
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
1.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 2
1.3. Conventions . . . . . . . . . . . . . . . . . . . . . . . 3
2. A Flow Label Option for IPv4 . . . . . . . . . . . . . . . . 3
2.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.1. The Flow Label Field of IPv6 . . . . . . . . . . . . 3
2.1.2. The Limitations of IntServ via IPv4 . . . . . . . . . 4
2.2. Definition of the Flow Label Option . . . . . . . . . . . 5
3. Translation between IPv6 and IPv4 . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
1.1. Terminology
This document uses the following terms:
* IntServ (Integrated Services): Reservation of network resources
(bandwidth) on a per-flow basis. See [RFC1633], [RFC2205],
[RFC2208], [RFC2209], [RFC2210], [RFC2211] and [RFC2212] for
details.
* Flow: An IntServ reservation between two endpoints.
* 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 [RFC6437],
[RFC6436] for detailed descriptions.
1.2. Abbreviations
* RSVP: ReSource Reservation Protocol
* SCTP: Stream Control Transmission Protocol
* TCP: Transmission Control Protocol
* QoS: Quality of Service
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* UDP: User Datagram Protocol
1.3. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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 (see [RFC6436] and [RFC6437]) of the IPv6 header
(see [RFC2460]) is a 20-bit 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:
* 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.
* Support for Network Layer Encryption: The mapping is independent
of payload encryption (e.g. by IPsec).
* 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.
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* 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.
* 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 [Dre2001],
[IJMUE2009] 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:
* 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!
* 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.
* 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
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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.
* 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.
* 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 [RFC0791]) 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* Type: 143
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* Length: 8 octets
* Flow Label: The 20-bit flow label. All definitions of [RFC6437]
and [RFC6436] 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 MUST 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.
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 MUST 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.
4. Security Considerations
Security considerations are similar to the IPv6 flow label, see
[RFC6437].
5. IANA Considerations
This document introduces no additional considerations for IANA.
6. Acknowledgments
The author would like to thank Brian E. Carpenter, Wes George, Perry
Lorier, Christoph Reichert and Michael Tuexen for their comments.
7. References
7.1. Normative References
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[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2205] Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
September 1997, <https://www.rfc-editor.org/info/rfc2205>.
[RFC2210] Wroclawski, J., "The Use of RSVP with IETF Integrated
Services", RFC 2210, DOI 10.17487/RFC2210, September 1997,
<https://www.rfc-editor.org/info/rfc2210>.
[RFC2211] Wroclawski, J., "Specification of the Controlled-Load
Network Element Service", RFC 2211, DOI 10.17487/RFC2211,
September 1997, <https://www.rfc-editor.org/info/rfc2211>.
[RFC2212] Shenker, S., Partridge, C., and R. Guerin, "Specification
of Guaranteed Quality of Service", RFC 2212,
DOI 10.17487/RFC2212, September 1997,
<https://www.rfc-editor.org/info/rfc2212>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <https://www.rfc-editor.org/info/rfc2460>.
[RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
"IPv6 Flow Label Specification", RFC 6437,
DOI 10.17487/RFC6437, November 2011,
<https://www.rfc-editor.org/info/rfc6437>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
7.2. Informative References
[RFC1633] Braden, R., Clark, D., and S. Shenker, "Integrated
Services in the Internet Architecture: an Overview",
RFC 1633, DOI 10.17487/RFC1633, June 1994,
<https://www.rfc-editor.org/info/rfc1633>.
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[RFC2208] Mankin, A., Ed., 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, DOI 10.17487/RFC2208, September 1997,
<https://www.rfc-editor.org/info/rfc2208>.
[RFC2209] Braden, R. and L. Zhang, "Resource ReSerVation Protocol
(RSVP) -- Version 1 Message Processing Rules", RFC 2209,
DOI 10.17487/RFC2209, September 1997,
<https://www.rfc-editor.org/info/rfc2209>.
[RFC6436] Amante, S., Carpenter, B., and S. Jiang, "Rationale for
Update to the IPv6 Flow Label Specification", RFC 6436,
DOI 10.17487/RFC6436, November 2011,
<https://www.rfc-editor.org/info/rfc6436>.
[Dre2001] Dreibholz, T., "Management of Layered Variable Bitrate
Multimedia Streams over DiffServ with Apriori
Knowledge", Masters Thesis, 20 February 2001,
<https://duepublico.uni-duisburg-
essen.de/servlets/DerivateServlet/Derivate-29936/
Dre2001.pdf>.
[IJMUE2009]
Zhu, W., Dreibholz, T., Rathgeb, E. P., and X. Zhou, "A
Scalable QoS Device for Broadband Access to Multimedia
Services", SERSC International Journal of Multimedia and
Ubiquitous Engineering (IJMUE) Number 2, Volume 4, Pages
157-172, ISSN 1975-0080, May 2009,
<http://www.sersc.org/journals/IJMUE/
vol4_no2_2009/14.pdf>.
Author's Address
Thomas Dreibholz
Simula Metropolitan Centre for Digital Engineering
Pilestredet 52
0167 Oslo
Norway
Email: dreibh@simula.no
URI: https://www.simula.no/people/dreibh
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