Internet DRAFT - draft-trammell-ipfix-tcpcontrolbits-revision
draft-trammell-ipfix-tcpcontrolbits-revision
IPFIX Working Group B. Trammell
Internet-Draft ETH Zurich
Intended status: Informational P. Aitken
Expires: June 7, 2014 Cisco Systems, Inc
December 4, 2013
Revision of the tcpControlBits IPFIX Information Element
draft-trammell-ipfix-tcpcontrolbits-revision-05.txt
Abstract
This document revises the tcpControlBits IPFIX Information Element as
originally defined in [RFC5102] to reflect changes to the TCP Flags
header field since [RFC0793].
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on June 7, 2014.
Copyright Notice
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document authors. All rights reserved.
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1. Introduction
Octets 12 and 13 (counting from zero) of the TCP header encode the
data offset (header length) in four bits, as well as 12 bits of
flags. The least significant 6 bits of these were defined in
[RFC0793] as URG, ACK, PSH, RST, SYN, and FIN for TCP control.
Subsequently, [RFC3168] defined the CWR and ECE flags for Explicit
Congestion Notification (ECN) negotiation and signaling; [RFC3540]
additionally defined the NS flag for the ECN Nonce Sum.
As defined in the IANA IPFIX Information Element Registry
[IANA-IPFIX], taken from [RFC5102], the tcpControlBits Information
Element for IPFIX [RFC7011] only covers the original six bits from
[RFC0793]. To allow IPFIX to be used to measure the use of ECN, and
to bring the IPFIX Information Element definition in line with the
current definition of the TCP Flags header field, it is necessary to
revise this definition.
The revised definition of the Information Element in Section 3 was
developed and approved through the IE-DOCTORS process [RFC7013] in
August 2013. Section 5.1 of [RFC7013] states "This process should
not in any way be construed as allowing the IE-DOCTORS to overrule
IETF consensus. Specifically, Information Elements in the IANA
Information Element registry which were added with IETF consensus
require IETF consensus for revision or deprecation". Since the
tcpControlBits Information Element was orignally defined in
[RFC5102], an IETF Proposed Standard, any revision of this
Information Element definition requires IETF Consensus. The
publication of this document fulfills that requirement.
The following section defines the revised tcpControlBits Information
Element as in Section 9.1 of [RFC7013].
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
[RFC2119].
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. 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
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any observed packet of this Flow has the corresponding TCP control
bit set to 1. The bit is cleared to 0 otherwise.
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 four 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 three 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.
If exported as a single octet with reduced size encoding, this
Information Element covers the low-order octet of this field (i.e,
bits 0x80 to 0x01), omitting the ECN Nonce Sum and the three
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Future Use bits. A collector receiving this Information Element
with reduced size encoding must not assume anything about the
content of these four bits.
Exporting Processes exporting this Information Element on behalf
of a Metering Process that is not capable of observing any of the
ECN Nonce Sum or Future Use bits 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 the CWR and ECE bits 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.
References: [RFC0793][RFC3168][RFC3540]
Revision: 1
4. IANA Considerations
IANA has updated the definition of the tcpControlBits Information
Element in the the IANA IPFIX Information Element Registry
[IANA-IPFIX] to reflect the changes in Section 3 above, setting the
revision to 1 as noted, and the revision date to the date of
publication of this document.
5. Security and Privacy Considerations
This document changes the data type (and therefore the native size)
of the tcpControlBits Information Element, from unsigned8 (1 octet)
to unsigned16 (2 octets). As Exporting and Collecting Processes use
the Information Element Length field in Templates and Options
Templates and specifications for reduced size encoding where
appropriate, as opposed to abstract data type sizes, for encoding and
decoding Data Records, it is not expected that this will have any
impact on buffer sizing during encoding and decoding. Otherwise,
note that the security considerations for IPFIX [RFC7011] apply.
6. Acknowledgments
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.
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7. References
7.1. Normative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, September 1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP", RFC
3168, September 2001.
[RFC3540] Spring, N., Wetherall, D., and D. Ely, "Robust Explicit
Congestion Notification (ECN) Signaling with Nonces", RFC
3540, June 2003.
[RFC7011] Claise, B., Trammell, B., and P. Aitken, "Specification of
the IP Flow Information Export (IPFIX) Protocol for the
Exchange of Flow Information", STD 77, RFC 7011, September
2013.
[RFC7013] Trammell, B. and B. Claise, "Guidelines for Authors and
Reviewers of IP Flow Information Export (IPFIX)
Information Elements", BCP 184, RFC 7013, September 2013.
7.2. Informative References
[RFC5102] Quittek, J., Bryant, S., Claise, B., Aitken, P., and J.
Meyer, "Information Model for IP Flow Information Export",
RFC 5102, January 2008.
[IANA-IPFIX]
Internet Assigned Numbers Authority, , "IP Flow
Information Export Information Elements
(http://www.iana.org/assignments/ipfix)", .
Authors' Addresses
Brian Trammell
Swiss Federal Institute of Technology Zurich
Gloriastrasse 35
8092 Zurich
Switzerland
Phone: +41 44 632 70 13
Email: trammell@tik.ee.ethz.ch
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Paul Aitken
Cisco Systems, Inc.
96 Commercial Quay
Commercial Street, Edinburgh EH6 6LX
United Kingdom
Phone: +44 131 561 3616
Email: paitken@cisco.com
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