Internet DRAFT - draft-ietf-opsawg-rfc7125-update
draft-ietf-opsawg-rfc7125-update
OPSAWG M. Boucadair
Internet-Draft Orange
Obsoletes: 7125 (if approved) 29 November 2023
Intended status: Standards Track
Expires: 1 June 2024
An Update to the tcpControlBits IP Flow Information Export (IPFIX)
Information Element
draft-ietf-opsawg-rfc7125-update-07
Abstract
RFC 7125 revised the tcpControlBits IP Flow Information Export
(IPFIX) Information Element that was originally defined in RFC 5102
to reflect changes to the TCP header control bits since RFC 793.
However, that update is still problematic for interoperability
because some flag values have subsequently been deprecated.
This document removes stale information from the IPFIX registry and
avoids future conflicts with the authoritative TCP Header Flags
registry.
This document obsoletes RFC 7125.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the Operations and
Management Area Working Group Working Group mailing list
(opsawg@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/opsawg/.
Source for this draft and an issue tracker can be found at
https://github.com/boucadair/-ipfix-rfc7125-update.
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 https://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on 1 June 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
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Revised tcpControlBits Information Element . . . . . . . . . 3
4. An Example . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Changes from RFC 7125 . . . . . . . . . . . . . . . 7
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 7
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
TCP defines a set of control bits (also known as "flags") for
managing connections (Section 3.1 of [RFC9293]). The "Transmission
Control Protocol (TCP) Header Flags" registry was initially set by
[RFC3168], but it was populated with only TCP control bits that were
defined in [RFC3168]. [RFC9293] fixed that by moving that registry
to be listed as a subregistry under the "Transmission Control
Protocol (TCP) Parameters" registry [TCP-FLAGS], adding bits that had
previously been specified in [RFC0793], and removing the NS (Nonce
Sum) bit as per [RFC8311]. Also, Section 6 of [RFC9293] introduces
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"Bit Offset" to ease referencing each header flag's offset within the
16-bit aligned view of the TCP header (Figure 1 of [RFC9293]).
[TCP-FLAGS] is thus settled as the authoritative reference for the
assigned TCP control bits.
Note: The bits in offsets 0 through 3 are not header flags, but
the TCP segment Data Offset field.
[RFC7125] revised the tcpControlBits IP Flow Information Export
(IPFIX) Information Element (IE) that was originally defined in
[RFC5102] to reflect changes to the TCP control bits since [RFC0793].
However, that update is still problematic for interoperability
because a value was deprecated since then (Section 7 of [RFC8311])
and, therefore, [RFC7125] risks deviating from the authoritative TCP
registry [TCP-FLAGS].
This document fixes that problem by removing stale information from
the IPFIX registry [IPFIX] and avoiding future conflicts with the
authoritative TCP registry [TCP-FLAGS]. The update in this document
is also useful to enhance observability. For example, network
operators can identify when packets are being observed with
unassigned TCP flags set and, therefore, identify which applications
in the network should be upgraded to reflect the changes to TCP flags
that were introduced, e.g., in [RFC8311].
The main changes to [RFC7125] are listed in Appendix A.
2. Terminology
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.
This document uses the terms defined in Section 2 of [RFC7011].
3. Revised tcpControlBits Information Element
ElementId: 6
Data Type: unsigned16
Data Type Semantics: flags
Description: TCP control bits observed for the packets of this Flow.
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This information is encoded as a bit field; each TCP control bit
has a corresponding bit in that field. A bit is set to 1 if any
observed packet of this Flow has the corresponding TCP control bit
set to 1. The bit is cleared to 0 otherwise.
As per [RFC9293], the assignment of the TCP control bits is
managed by IANA from the "TCP Header Flags" registry [TCP-FLAGS].
That registry is authoritative to retrieve the most recent TCP
control bits.
As the most significant 4 bits of octets 12 and 13 (counting from
zero) of the TCP header [RFC9293] are used to encode the TCP data
offset (header length), the corresponding bits in this Information
Element MUST be reported by the Exporter with a value of zero and
MUST be ignored by the Collector. Use the tcpHeaderLength
Information Element to encode this value.
All TCP control bits (including those unassigned) MUST be exported
as observed in the TCP headers of the packets of this Flow.
If exported as a single octet with reduced-size encoding
(Section 6.2 of [RFC7011]), this Information Element covers the
low-order octet of this field (i.e., bit offset positions 8 to 15)
[TCP-FLAGS]. A Collector receiving this Information Element with
reduced-size encoding must not assume anything about the content
of the four bits with bit offset positions 4 to 7.
Exporting Processes exporting this Information Element on behalf
of a Metering Process that is not capable of observing any of the
flags with bit offset positions 4 to 7 SHOULD use reduced-size
encoding, and only export the least significant 8 bits of this
Information Element.
Note that previous revisions of this Information Element's
definition specified that flags with bit offset positions 8 and 9
must be exported as zero, even if observed. Collectors should
therefore not assume that a value of zero for these bits in this
Information Element indicates the bits were never set in the
observed traffic, especially if these bits are zero in every Flow
Record sent by a given Exporter.
Note also that [TCP-FLAGS] indexes the bit offset from the most-
significant bit of octet 12 to the least-significant bit of octet
13 in the TCP header, but the tcpControlBits is encoded as a
regular unsigned 16 bit integer.
Units:
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Range:
References: [RFC9293][This-Document]
Additional Information: See the assigned TCP control bits in
[TCP-FLAGS].
Revision: 2
4. An Example
Figure 1 shows an example of a tcpControlBits Information Element set
to 146. This Information Element is used to report TCP control bits
for a Flow that has CWR (Congestion Window Reduced), ACK, and SYN
flag bits set (that is, bit offset positions 8, 11, and 14).
MSB LSB
1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0|0|0|0|0|0|0|1|0|0|1|0|0|1|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: An Example of tcpControlBits Information Element
5. IANA Considerations
IANA is requested to update the "tcpControlBits" entry of the [IPFIX]
to echo the details provided in Section 3.
6. Security Considerations
Because the setting of TCP control bits may be misused in some flows
(e.g., Distributed Denial-of-Service (DDoS) attacks), an Exporter has
to report all observed control bits even if no meaning is associated
with a given TCP flag. This document uses a stronger requirements
language compared to [RFC7125].
This document does not add new security considerations to those
already discussed for IPFIX in [RFC7011].
7. References
7.1. Normative References
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[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/rfc/rfc2119>.
[RFC7011] Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
"Specification of the IP Flow Information Export (IPFIX)
Protocol for the Exchange of Flow Information", STD 77,
RFC 7011, DOI 10.17487/RFC7011, September 2013,
<https://www.rfc-editor.org/rfc/rfc7011>.
[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/rfc/rfc8174>.
[RFC9293] Eddy, W., Ed., "Transmission Control Protocol (TCP)",
STD 7, RFC 9293, DOI 10.17487/RFC9293, August 2022,
<https://www.rfc-editor.org/rfc/rfc9293>.
[TCP-FLAGS]
IANA, "TCP Header Flags", n.d.,
<https://www.iana.org/assignments/tcp-parameters/tcp-
parameters.xhtml#tcp-header-flags>.
7.2. Informative References
[IPFIX] IANA, "IP Flow Information Export (IPFIX) Entities", n.d.,
<https://www.iana.org/assignments/ipfix/ipfix.xhtml>.
[RFC0793] Postel, J., "Transmission Control Protocol", RFC 793,
DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/rfc/rfc793>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/rfc/rfc3168>.
[RFC5102] Quittek, J., Bryant, S., Claise, B., Aitken, P., and J.
Meyer, "Information Model for IP Flow Information Export",
RFC 5102, DOI 10.17487/RFC5102, January 2008,
<https://www.rfc-editor.org/rfc/rfc5102>.
[RFC7125] Trammell, B. and P. Aitken, "Revision of the
tcpControlBits IP Flow Information Export (IPFIX)
Information Element", RFC 7125, DOI 10.17487/RFC7125,
February 2014, <https://www.rfc-editor.org/rfc/rfc7125>.
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[RFC8311] Black, D., "Relaxing Restrictions on Explicit Congestion
Notification (ECN) Experimentation", RFC 8311,
DOI 10.17487/RFC8311, January 2018,
<https://www.rfc-editor.org/rfc/rfc8311>.
[RFC9487] Graf, T., Claise, B., and P. Francois, "Export of Segment
Routing over IPv6 Information in IP Flow Information
Export (IPFIX)", RFC 9487, DOI 10.17487/RFC9487, November
2023, <https://www.rfc-editor.org/rfc/rfc9487>.
Appendix A. Changes from RFC 7125
* Clean-up the description by removing mentions of stale flag bits,
referring to the flag bits by their bit offset position, and
relying upon the IANA TCP registry.
* Remove the table of TCP flag bits from the description of the
tcpControlBits Information Element.
* Add [TCP-FLAGS] to the Additional Information field of the
tcpControlBits Information Element.
* Use strong normative language for exporting observed flags.
* Update the references of the tcpControlBits Information Element.
* Bump the revision of the tcpControlBits Information Element.
* Replace obsolete RFCs (e.g., [RFC0793]).
* Add an Example Section
Acknowledgments
This document was triggered by a discussion of the author in opsawg
with the authors of [RFC9487].
Thanks to Christian Jacquenet, Thomas Graf, and Benoît Claise for the
review and comments.
Thanks to Michael Scharf for the tsvart review, Ketan Talaulikar for
the rtgdir review, and Elwyn Davies for the genart review.
Thanks to Rob Wilton for the AD review.
Thanks for Tim Bray for the artart review and Shawn Emery for the
secdir review.
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Thanks to Éric Vyncke and Paul Wouters for the comments in the IESG
review.
Acknowledgments from [RFC7125]: Thanks to Andrew Feren, Lothar
Braun, Michael Scharf, and Simon Josefsson for comments on the
revised definition. This work is partially supported by the
European Commission under grant agreement FP7-ICT-318627 mPlane;
this does not imply endorsement by the Commission.
Contributors
The authors of [RFC7125] are as follows:
* Brian Trammell
* Paul Aitken
Author's Address
Mohamed Boucadair
Orange
35000 Rennes
France
Email: mohamed.boucadair@orange.com
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