Internet DRAFT - draft-mizrahi-intarea-packet-timestamps
draft-mizrahi-intarea-packet-timestamps
Network Working Group T. Mizrahi
Internet-Draft Marvell
Intended status: Informational J. Fabini
Expires: March 28, 2018 Vienna University of Technology
A. Morton
AT&T Labs
September 24, 2017
Guidelines for Defining Packet Timestamps
draft-mizrahi-intarea-packet-timestamps-01
Abstract
This document specifies guidelines for defining binary packet
timestamp formats in networking protocols at various layers. It also
presents three recommended timestamp formats. The target audience of
this memo includes network protocol designers. It is expected that a
new network protocol that requires a packet timestamp will, in most
cases, use one of the recommended timestamp formats. If none of the
recommended formats fits the protocol requirements, the new protocol
specification should specify the format of the packet timestamp
according to the guidelines in this document.
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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material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 28, 2018.
Copyright Notice
Copyright (c) 2017 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
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 3
3. Packet Timestamp Format Specification . . . . . . . . . . . . 3
4. Recommended Timestamp Formats . . . . . . . . . . . . . . . . 4
4.1. Using a Recommended Timestamp Format . . . . . . . . . . 5
4.2. NTP Timestamp Formats . . . . . . . . . . . . . . . . . . 5
4.2.1. NTP 64-bit Timestamp Format . . . . . . . . . . . . . 5
4.2.2. NTP 32-bit Timestamp Format . . . . . . . . . . . . . 6
4.3. The PTP Truncated Timestamp Format . . . . . . . . . . . 8
5. Timestamp Use Cases . . . . . . . . . . . . . . . . . . . . . 9
5.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . . . 9
5.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Packet Timestamp Control Field . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Security Considerations . . . . . . . . . . . . . . . . . . . 11
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . 12
10.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
Timestamps are widely used in network protocols for various purposes,
including delay measurement, clock synchronization, and logging or
reporting the time of an event.
Timestamps are represented in the RFC series in one of two forms:
text-based timestamps, and packet timestamps. Text-based timestamps
[RFC3339] are represented as user-friendly strings, and are widely
used in the RFC series, for example in information objects and data
models, e.g., [RFC5646], [RFC6991], and [RFC7493]. Packet
timestamps, on the other hand, are represented by a compact binary
field that has a fixed size, and are not intended to have a human-
friendly format. Packet timestamps are also very common in the RFC
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series, and are used for example for measuring delay and for
synchronizing clocks, e.g., [RFC5905], [RFC4656], and [RFC1323].
This memo presents guidelines for defining a packet timestamp format
in network protocols. Three recommended timestamp formats are
presented. It is expected that a new network protocol that requires
a packet timestamp will, in most cases, use one of the recommended
timestamp formats. If none of the recommended formats fits the
protocol requirements, the new protocol specification should specify
the format of the packet timestamp according to the guidelines in
this document.
2. Terminology
2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2.2. Abbreviations
NTP Network Time Protocol [RFC5905]
PTP Precision Time Protocol [IEEE1588]
3. Packet Timestamp Format Specification
This memo recommends to use the timestamp formats defined in
Section 4. In cases where these timestamp formats do not satisfy the
protocol requirements, the timestamp specification should clearly
state the reasons for defining a new format. Moreover, it is
recommended to derive the new timestamp format from an existing
timestamp format, either a timestamp format from this memo, or any
other previously defined timestamp format.
This section defines a template for specifying packet timestamp
formats. A timestamp format specification MUST include the following
aspects:
Timestamp field format:
The format of the timestamp field consists of:
+ Size: The number of bits (or octets) used to represent the
packet timestamp field.
+ Units: The units used to represent the timestamp.
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If the timestamp is comprised of more than one field, the format
of each field is specified.
Epoch:
The origin of the timescale used for the timestamp; the moment in
time used as a reference for the timestamp value.
Resolution:
The timestamp resolution; the resolution is equal to the timestamp
field unit. If the timestamp consists of two or more fields using
different time units, then the resolution is the smallest time
unit.
Wraparound:
The wraparound period of the timestamp; any further wraparound-
related considerations should be described here.
4. Recommended Timestamp Formats
This memo recommends to use one of the timestamp formats specified
below.
Clearly, different network protocols may have different requirements
and constraints, and consequently may use different timestamp
formats. The choice of the specific timestamp format for a given
protocol may depend on a various factors. A few examples of factors
that may affect the choice of the timestamp format:
o Timestamp size: while some network protocols may allow a large
timestamp fields, in other cases there may be constraints with
respect to the timestamp size, affecting the choice of the
timestamp format.
o Resolution: the time resolution is another factor that may
directly affect the selected timestamp format. Similarly, the
wraparound periodicity of the timestamp may also affect the
selected format.
o Wraparound period: the length of the time interval in which the
timestamp is unique may also be an important factor in choosing
the timestamp format. Along with the timestamp resolution, these
two factors determine the required number of bits in the
timestamp.
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o Common format for multiple protocols: if there are two or more
network protocols that use timestamps and are often used together
in typical systems, using a common timestamp format should be
preferred if possible. Specifically, if the network protocol that
is being defined typically runs on a PC, then an NTP-based
timestamp format may allow easier integration with an NTP-
synchronized timer. In contrast, a protocol that is typically
deployed on a hardware-based platform, may make better use of a
PTP-based timestamp, allowing more efficient integration with a
PTP-synchronized timer.
4.1. Using a Recommended Timestamp Format
A specification that uses one of the recommended timestamp formats
should specify explicitly that this is a recommended timestamp
format, and point to the relevant section in the current memo.
A specification that uses one of the recommended timestamp formats
should also include a section on Synchronization Aspects. Any
assumptions or requirements related to synchronization should be
specified in this section. For example, the synchronization aspects
may specify whether nodes populating the timestamps should be
synchronized among themselves, and whether the timestamp is measured
with respect to a central reference clock such as an NTP server. If
time is assumed to be synchronized to a time standard such as UTC or
TAI, it should be specified in this section. Further considerations
may be discussed in this section, such as required accuracy, or leap
second handling.
4.2. NTP Timestamp Formats
4.2.1. NTP 64-bit Timestamp Format
The Network Time Protocol (NTP) 64-bit timestamp format is defined in
[RFC5905]. This timestamp format is used in several network
protocols, including [RFC6374], [RFC4656], and [RFC5357]. Since this
timestamp format is used in NTP, this timestamp format should be
preferred in network protocols that are typically deployed in concert
with NTP.
The format is presented in this section according to the template
defined in Section 3.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Seconds |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Fraction |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: NTP [RFC5905] 64-bit Timestamp Format
Timestamp field format:
Seconds: specifies the integer portion of the number of seconds
since the epoch.
+ Size: 32 bits.
+ Units: seconds.
Fraction: specifies the fractional portion of the number of
seconds since the epoch.
+ Size: 32 bits.
+ Units: the unit is 2^(-32) seconds, which is roughly equal to
233 picoseconds.
Epoch:
The epoch is 1 January 1900 at 00:00 UTC.
Resolution:
The resolution is 2^(-32) seconds.
Wraparound:
This time format wraps around every 2^32 seconds, which is roughly
136 years. The next wraparound will occur in the year 2036.
4.2.2. NTP 32-bit Timestamp Format
The Network Time Protocol (NTP) 32-bit timestamp format is defined in
[RFC5905]. This timestamp format is used in
[I-D.morton-ippm-mbm-registry]. This timestamp format should be
preferred in network protocols that are typically deployed in concert
with NTP. The 32-bit format can be used either when space
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constraints do not allow the use of the 64-bit format, or when the
32-bit format satisfies the resolution and wraparound requirements.
The format is presented in this section according to the template
defined in Section 3.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Seconds | Fraction |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: NTP [RFC5905] 32-bit Timestamp Format
Timestamp field format:
Seconds: specifies the integer portion of the number of seconds
since the epoch.
+ Size: 16 bits.
+ Units: seconds.
Fraction: specifies the fractional portion of the number of
seconds since the epoch.
+ Size: 16 bits.
+ Units: the unit is 2^(-16) seconds, which is roughly equal to
15.3 microseconds.
Epoch:
The epoch is 1 January 1900 at 00:00 UTC.
Resolution:
The resolution is 2^(-16) seconds.
Wraparound:
This time format wraps around every 2^16 seconds, which is roughly
18 hours.
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4.3. The PTP Truncated Timestamp Format
The Precision Time Protocol (PTP) [IEEE1588] uses an 80-bit timestamp
format. The truncated timestamp format is a 64-bit field, which is
the 64 least significant bits of the 80-bit PTP timestamp. Since
this timestamp format is similar to the one used in PTP, this
timestamp format should be preferred in network protocols that are
typically deployed in PTP-capable devices.
The PTP truncated timestamp format is used in several protocols, such
as [RFC6374], [RFC7456], [RFC8186] and [ITU-T-Y.1731].
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Seconds |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nanoseconds |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: PTP [IEEE1588] Truncated Timestamp Format
Timestamp field format:
Seconds: specifies the integer portion of the number of seconds
since the epoch.
+ Size: 32 bits.
+ Units: seconds.
Nanoseconds: specifies the fractional portion of the number of
seconds since the epoch.
+ Size: 32 bits.
+ Units: nanoseconds. The value of this field is in the range 0
to (10^9)-1.
Epoch:
The PTP [IEEE1588] epoch is 1 January 1970 00:00:00 TAI, which is
31 December 1969 23:59:51.999918 UTC.
Resolution:
The resolution is 1 nanosecond.
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Wraparound:
This time format wraps around every 2^32 seconds, which is roughly
136 years. The next wraparound will occur in the year 2106.
5. Timestamp Use Cases
Packet timestamps are used in various network protocols. Typical
applications of packet timestamps include delay measurement, clock
synchronization, and others. The following table presents a (non-
exhaustive) list of protocols that use packet timestamps, and the
timestamp formats used in each of these protocols.
+------------------+-----------------------------------+-----------+
| | Recommended formats | Other |
+------------------+-----------+-----------+-----------+ format |
| Protocol |NTP 64-bit |NTP 32-bit |PTP Trunc. | |
+------------------+-----------+-----------+-----------+-----------+
| NTP [RFC5905] | + | | | |
+------------------+-----------+-----------+-----------+-----------+
| OWAMP [RFC4656] | + | | | |
+------------------+-----------+-----------+-----------+-----------+
| TWAMP [RFC5357] | + | | | |
| TWAMP [RFC8186] | | | + | |
+------------------+-----------+-----------+-----------+-----------+
| TRILL [RFC7456] | | | + | |
+------------------+-----------+-----------+-----------+-----------+
| MPLS [RFC6374] | | | + | |
+------------------+-----------+-----------+-----------+-----------+
| TCP [RFC1323] | | | | + |
+------------------+-----------+-----------+-----------+-----------+
| RTP [RFC3550] | + | | | + |
+------------------+-----------+-----------+-----------+-----------+
Figure 4: Protocols that use Packet Timestamps
The rest of this section presents two hypothetic examples of network
protocol specifications that use one of the recommended timestamp
formats. The examples include the text that specifies the
information related to the timestamp format.
5.1. Example 1
Timestamp:
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The timestamp format used in this specification is the NTP
[RFC5905] 64-bit format, as specified in Section 4.2.1 of
[I-D.mizrahi-intarea-packet-timestamps].
Synchronization aspects:
It is assumed that nodes that run this protocol are synchronized
to UTC using a synchronization mechanism that is outside the scope
of this document. In typical deployments this protocol will be
run on a machine that uses NTP [RFC5905] for synchronization.
Thus, the timestamp may be derived from the NTP-synchronized
clock, allowing the timestamp to be measured with respect to the
clock of an NTP server.
5.2. Example 2
Timestamp:
The timestamp format used in this specification is the PTP
[IEEE1588] Truncated format, as specified in Section 4.2.3 of
[I-D.mizrahi-intarea-packet-timestamps].
Synchronization aspects:
It is assumed that nodes that run this protocol are synchronized
among themselves. Nodes may be synchronized to a global reference
time. Note that if PTP [IEEE1588] is used for synchronization,
the timestamp may be derived from the PTP-synchronized clock,
allowing the timestamp to be measured with respect to the clock of
an PTP Grandmaster clock.
6. Packet Timestamp Control Field
In some cases it is desirable to have a control field that includes
information about the timestamp format. This section defines a
recommended format of a timestamp-related control field that is
intended for network protocols that require such timestamp-related
control information.
The recommended control field includes the following sub-fields:
o Timestamp format.
o Precision - the resolution or granularity of the system clock.
o Epoch.
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o Era - the number of times the time has wrapped around since the
epoch.
7. IANA Considerations
This memo includes no request to IANA.
8. Security Considerations
A network protocol that uses a packet timestamp MUST specify the
security considerations that result from using the timestamp. This
section provides an overview of some of the common security
considerations of using timestamps.
Any metadata that is attached to control or data packets, and
specifically packet timestamps, can facilitate network
reconnaissance; by passively eavesdropping to timestamped packets an
attacker can gather information about the network performance, and
about the level of synchronization between nodes.
Timestamps can be spoofed or modified by on-path attackers, thus
attacking the application that uses the timestamps. For example, if
timestamps are used in a delay measurement protocol, an attacker can
modify en route timestamps in a way that manipulates the measurement
results. Integrity protection mechanisms, such as Hashed Message
Authentication Codes (HMAC), can mitigate such attacks. The
specification of an integrity protection mechanism is outside the
scope of this document, as typically integrity protection will be
defined on a per-network-protocol basis, and not specifically for the
timestamp field.
Another potential threat that can have a similar impact is delay
attacks. An attacker can maliciously delay some or all of the en
route messages, with the same harmful implications as described in
the previous paragraph. Mitigating delay attacks is a significant
challenge; in contrast to spoofing and modification attacks, the
delay attack cannot be prevented by cryptographic integrity
protection mechanisms. In some cases delay attacks can be mitigated
by sending the timestamped information through multiple paths,
allowing to detect and to be resilient to an attacker that has access
to one of the paths.
In many cases timestamping relies on an underlying synchronization
mechanism. Thus, any attack that compromises the synchronization
mechanism can also compromise protocols that use timestamping.
Attacks on time protocols are discussed in detail in [RFC7384].
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9. Acknowledgments
The authors thank Yaakov Stein and other members of the TICTOC and
NTP working groups for many helpful comments.
10. References
10.1. 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/info/rfc2119>.
10.2. Informative References
[I-D.mizrahi-intarea-packet-timestamps]
Mizrahi, T., Fabini, J., and A. Morton, "Guidelines for
Defining Packet Timestamps", draft-mizrahi-intarea-packet-
timestamps-00 (work in progress), June 2017.
[I-D.morton-ippm-mbm-registry]
Morton, A. and M. Mathis, "Initial Performance Metric
Registry Entries Part 2: MBM", draft-morton-ippm-mbm-
registry-01 (work in progress), March 2017.
[IEEE1588]
IEEE, "IEEE 1588 Standard for a Precision Clock
Synchronization Protocol for Networked Measurement and
Control Systems Version 2", 2008.
[ITU-T-Y.1731]
ITU-T, "OAM functions and mechanisms for Ethernet based
Networks", 2013.
[RFC1323] Jacobson, V., Braden, R., and D. Borman, "TCP Extensions
for High Performance", RFC 1323, DOI 10.17487/RFC1323, May
1992, <https://www.rfc-editor.org/info/rfc1323>.
[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
<https://www.rfc-editor.org/info/rfc3339>.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
July 2003, <https://www.rfc-editor.org/info/rfc3550>.
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[RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
Zekauskas, "A One-way Active Measurement Protocol
(OWAMP)", RFC 4656, DOI 10.17487/RFC4656, September 2006,
<https://www.rfc-editor.org/info/rfc4656>.
[RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
RFC 5357, DOI 10.17487/RFC5357, October 2008,
<https://www.rfc-editor.org/info/rfc5357>.
[RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
September 2009, <https://www.rfc-editor.org/info/rfc5646>.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<https://www.rfc-editor.org/info/rfc5905>.
[RFC6374] Frost, D. and S. Bryant, "Packet Loss and Delay
Measurement for MPLS Networks", RFC 6374,
DOI 10.17487/RFC6374, September 2011,
<https://www.rfc-editor.org/info/rfc6374>.
[RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types",
RFC 6991, DOI 10.17487/RFC6991, July 2013,
<https://www.rfc-editor.org/info/rfc6991>.
[RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in
Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384,
October 2014, <https://www.rfc-editor.org/info/rfc7384>.
[RFC7456] Mizrahi, T., Senevirathne, T., Salam, S., Kumar, D., and
D. Eastlake 3rd, "Loss and Delay Measurement in
Transparent Interconnection of Lots of Links (TRILL)",
RFC 7456, DOI 10.17487/RFC7456, March 2015,
<https://www.rfc-editor.org/info/rfc7456>.
[RFC7493] Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
DOI 10.17487/RFC7493, March 2015,
<https://www.rfc-editor.org/info/rfc7493>.
[RFC8186] Mirsky, G. and I. Meilik, "Support of the IEEE 1588
Timestamp Format in a Two-Way Active Measurement Protocol
(TWAMP)", RFC 8186, DOI 10.17487/RFC8186, June 2017,
<https://www.rfc-editor.org/info/rfc8186>.
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Authors' Addresses
Tal Mizrahi
Marvell
6 Hamada st.
Yokneam
Israel
Email: talmi@marvell.com
Joachim Fabini
Vienna University of Technology
Gusshausstrasse 25/E389
Vienna 1040
Austria
Phone: +43 1 58801 38813
Fax: +43 1 58801 38898
Email: Joachim.Fabini@tuwien.ac.at
URI: http://www.tc.tuwien.ac.at/about-us/staff/joachim-fabini/
Al Morton
AT&T Labs
200 Laurel Avenue South
Middletown,, NJ 07748
USA
Phone: +1 732 420 1571
Fax: +1 732 368 1192
Email: acmorton@att.com
URI: http://home.comcast.net/~acmacm/
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