OPSAWG M. Boucadair
Internet-Draft Orange
Obsoletes: 7125 (if approved) 26 March 2023
Intended status: Standards Track
Expires: 27 September 2023
An Update to the tcpControlBits IP Flow Information Export (IPFIX)
Information Element
draft-ietf-opsawg-rfc7125-update-02
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 Flags header field since RFC 793.
However, that update is still problematic for interoperability
because some flag values were deprecated since then.
This document removes stale information from the IPFIX registry and
avoiding 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 27 September 2023.
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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. The tcpControlBits Information Element . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1. Normative References . . . . . . . . . . . . . . . . . . 5
6.2. Informative References . . . . . . . . . . . . . . . . . 5
Appendix A. Changes from RFC 7125 . . . . . . . . . . . . . . . 6
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 7
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
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, 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 "Bit Offset"
to ease referencing each header flag's offset within the 16-bit
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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.
[RFC7125] revised the tcpControlBits IP Flow Information Export
(IPFIX) Information Element (IE) that was originally defined in
[RFC5102] to reflect changes to the TCP Flags header field 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 to deviate from the
authoritative TCP registry [TCP-FLAGS]. This update 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].
This document fixes that problem by removing stale information from
the IPFIX registry and avoiding future conflicts with the
authoritative TCP registry [IPFIX].
Also, 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
requirement language compared to [RFC7125]. See Section 3 for more
details.
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. The 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; for each TCP control
bit, there is a bit in this set. The 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 exported 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, 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 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.
Units:
Range:
References: [RFC9293][This-Document]
Revision: 2
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4. IANA Considerations
IANA is requested to update the "tcpControlBits" entry of the [IPFIX]
as follows:
* Update the description of to reflect the change in Section 3.
* Add [TCP-FLAGS] to the Additional Information field.
* Set the revision to 2 and the revision date to the date of
publication of this document.
* Add this document to the references.
5. Security Considerations
This document does not add new security considerations to those
already discussed for IPFIX in [RFC7011].
6. References
6.1. Normative References
[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>.
6.2. Informative References
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[I-D.ietf-opsawg-ipfix-srv6-srh]
Graf, T., Claise, B., and P. Francois, "Export of Segment
Routing over IPv6 Information in IP Flow Information
Export (IPFIX)", Work in Progress, Internet-Draft, draft-
ietf-opsawg-ipfix-srv6-srh-07, 13 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-opsawg-
ipfix-srv6-srh-07>.
[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>.
[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>.
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.
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* Update the references of the tcpControlBits Information Element.
* Bump the revision of the tcpControlBits Information Element.
* Replace obsolete RFCs (e.g., RFC793).
Acknowledgments
This document was triggered by a discussion of the author in opsawg
with the authors of [I-D.ietf-opsawg-ipfix-srv6-srh].
Thanks to Christian Jacquenet, Thomas Graf, and Benoît Claise for the
review and comments.
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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