OPSAWG M. Boucadair
Internet-Draft Orange
Updates: 7125 (if approved) 24 February 2023
Intended status: Standards Track
Expires: 28 August 2023
An Update to the tcpControlBits IP Flow Information Export (IPFIX)
Information Element
draft-ietf-opsawg-rfc7125-update-01
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 updates RFC 7125 by removing stale information from the
IPFIX registry and avoiding future conflicts with the authoritative
TCP Header Flags registry.
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 28 August 2023.
Copyright Notice
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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. An Update to tcpControlBits IP Flow Information Export (IPFIX)
Information Element . . . . . . . . . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1. Normative References . . . . . . . . . . . . . . . . . . 5
6.2. Informative References . . . . . . . . . . . . . . . . . 6
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 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
aligned view of the TCP header (Figure 1 of [RFC9293]). [TCP-FLAGS]
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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. An Update to tcpControlBits IP Flow Information Export (IPFIX)
Information Element
This document updates Section 3 of [RFC7125] as follows:
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OLD:
The values of each bit are shown below, per the definition of the
bits in the TCP header [RFC0793][RFC3168][RFC3540]:
MSb LSb
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| | | N | C | E | U | A | P | R | S | F |
| Zero | Future | S | W | C | R | C | S | S | Y | I |
| (Data Offset) | Use | | R | E | G | K | H | T | N | N |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
bit flag
value name description
------+-----+-------------------------------------
0x8000 Zero (see tcpHeaderLength)
0x4000 Zero (see tcpHeaderLength)
0x2000 Zero (see tcpHeaderLength)
0x1000 Zero (see tcpHeaderLength)
0x0800 Future Use
0x0400 Future Use
0x0200 Future Use
0x0100 NS ECN Nonce Sum
0x0080 CWR Congestion Window Reduced
0x0040 ECE ECN Echo
0x0020 URG Urgent Pointer field significant
0x0010 ACK Acknowledgment field significant
0x0008 PSH Push Function
0x0004 RST Reset the connection
0x0002 SYN Synchronize sequence numbers
0x0001 FIN No more data from sender
As the most significant 4 bits of octets 12 and 13 (counting from
zero) of the TCP header [RFC0793] are used to encode the TCP data
offset (header length), the corresponding bits in this Information
Element MUST be exported as zero and MUST be ignored by the
collector. Use the tcpHeaderLength Information Element to encode
this value.
Each of the 3 bits (0x800, 0x400, and 0x200), which are reserved
for future use in [RFC0793], SHOULD be exported as observed in the
TCP headers of the packets of this Flow.
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NEW:
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.
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.
* Add this document to the references.
5. Security Considerations
This document does not add any new security considerations to those
already discussed in Section 5 of [RFC7125].
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>.
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[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>.
[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
[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-06, 5 January 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-opsawg-
ipfix-srv6-srh-06>.
[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>.
[RFC3540] Spring, N., Wetherall, D., and D. Ely, "Robust Explicit
Congestion Notification (ECN) Signaling with Nonces",
RFC 3540, DOI 10.17487/RFC3540, June 2003,
<https://www.rfc-editor.org/rfc/rfc3540>.
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[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>.
[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>.
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.
Author's Address
Mohamed Boucadair
Orange
35000 Rennes
France
Email: mohamed.boucadair@orange.com
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