Network Working Group T. Mizrahi
Internet-Draft Huawei
Intended status: Informational I. Yerushalmi
Expires: December 19, 2021 D. Melman
Marvell
R. Browne
Intel
June 17, 2021
Network Service Header (NSH) Context Header Allocation: Timestamp
draft-mymb-sfc-nsh-allocation-timestamp-09
Abstract
The Network Service Header (NSH) specification defines two possible
methods of including metadata (MD): MD Type 0x1 and MD Type 0x2. MD
Type 0x1 uses a fixed-length Context Header. The allocation of this
Context Header, i.e., its structure and semantics, has not been
standardized. This memo presents an allocation for the fixed Context
Headers of NSH, which incorporates the packet's timestamp, a sequence
number, and a source interface identifier.
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 December 19, 2021.
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 4
3. NSH Timestamp Context Header Allocation . . . . . . . . . . . 4
4. Timestamping Use Cases . . . . . . . . . . . . . . . . . . . 6
4.1. Network Analytics . . . . . . . . . . . . . . . . . . . . 6
4.2. Alternate Marking . . . . . . . . . . . . . . . . . . . . 6
4.3. Consistent Updates . . . . . . . . . . . . . . . . . . . 7
5. Synchronization Considerations . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The Network Service Header (NSH), defined in [RFC8300], is an
encapsulation header that is used as the service encapsulation in the
Service Function Chains (SFC) architecture [RFC7665].
In order to share metadata along a service path, the NSH
specification [RFC8300] supports two methods: a fixed-length Context
Header (MD Type 0x1) and a variable-length Context Header (MD Type
0x2). When using MD Type 0x1 the NSH includes 16 octets of Context
Header fields.
The NSH specification [RFC8300] has not defined the semantics of the
16-octet Context Header, nor how it is used by NSH-aware service
functions, SFFs and proxies. Some allocation schemes were proposed
in the past to acoommodate specific use cases, e.g.,
[I-D.ietf-sfc-nsh-dc-allocation] and
[I-D.ietf-sfc-nsh-broadband-allocation].
This memo defines an allocation for the MD Type 0x1 Context Header,
which incorporates the timestamp of the packet, a sequence number,
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and a source interface identifier. It is noted that other MD Type
0x1 allocations might be specified in the future. Although MD Type
0x1 allocations are currently not being standardized by the SFC
working group, a consistent format (allocation) should be used in an
SFC-enabled domain in order to allow interoperability.
In a nutshell, packets that enter the SFC-enabled domain are
timestamped by a Classifier [RFC7665]. Thus, the timestamp, sequence
number and source interface are incorporated in the NSH Context
Header. As defined in [RFC8300], if reclassification is used, it may
result in an update to the NSH metadata. Specifically, when the
Timestamp Context Header is used, a reclassifier may either leave it
unchanged, or update the three fields: timestamp, sequence number and
source interface.
The Timestamp Context Header includes three fields that may be used
for various purposes. The timestamp field may be used for logging,
troubleshooting, delay measurement, packet marking for performance
monitoring, and timestamp-based policies. The source interface
identifier indicates the interface through which the packet was
received at the classifier. This identifier may specify a physical
or a virtual interface. The sequence numbers can be used by Service
Functions (SFs) to detect out-of-order delivery or duplicate
transmissions. Note that duplicate packet detection is possible when
multiple copies are received by the same SF, but is not necessarily
possible when there are multiple instances of the same SF and
duplicate copies of a packet are spread across different instances of
the SF. The sequence number is maintained on a per-source-interface
basis.
This document presents the Timestamp Context Header, but does not
specify the functionality of the SFs that receive the Context Header.
Although a few possible use cases are described in the document, the
SF behavior and application are outside the scope of this document.
KPI-stamping [RFC8592] defines an NSH timestamping mechanism that
uses the MD Type 0x2 format. The current memo defines a compact MD
Type 0x1 Context Header that does not require the packet to be
extended beyond the NSH header. Furthermore, the two timestamping
mechanisms can be used in concert, as further discussed in
Section 4.1.
2. Terminology
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2.1. Requirements Language
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.
2.2. Abbreviations
The following abbreviations are used in this document:
KPI Key Performance Indicators [RFC8592]
NSH Network Service Header [RFC8300]
MD Metadata [RFC8300]
SF Service Function [RFC7665]
SFC Service Function Chaining [RFC7665]
3. NSH Timestamp Context Header Allocation
This memo defines the following fixed-length Context Header
allocation, as presented in Figure 1.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Interface |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: NSH Timestamp Allocation.
The NSH Timestamp Allocation that is defined in this memo MUST
include the following fields:
o Sequence Number - a 32-bit sequence number. The sequence number
is maintained on a per-source-interface basis. Sequence numbers
can be used by SFs to detect out-of-order delivery, or duplicate
transmissions. The Classifier increments the sequence number by 1
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for each packet received through the source interface. This
requires the classifier to maintain a per-source-interface
counter. The sequence number is initialized to a random number on
startup. After it reaches its maximal value (2^32-1) the sequence
number wraps around back to zero.
o Source Interface - a 32-bit source interface identifier that is
assigned by the Classifier. The source interface is unique in the
context of the given classifier.
o Timestamp - this field is 8 octets long, and specifies the time at
which the packet was received by the Classifier. Two possible
timestamp formats can be used for this field: the two 64-bit
recommended formats specified in [RFC8877]. One of the formats is
based on the [IEEE1588] timestamp format, and the other is based
on the [RFC5905] format.
The NSH specification [RFC8300] does not specify the possible
coexistence of multiple MD Type 0x1 Context Header formats in a
single SFC-enabled domain. It is assumed that the Timestamp Context
Header will be deployed in an SFC-enabled domain that uniquely uses
this Context Header format. Thus, operators SHOULD ensure that
either a consistent Context Header format is used in the SFC-enabled
domain, or that there is a clear policy that allows SFs to know the
Context Header format of each packet. Specifically, operators are
expected to ensure the consistent use of a timestamp format across
the whole SFC-enabled domain.
The two timestamp formats that can be used in the timestamp field
are:
o IEEE 1588 Truncated Timestamp Format: this format is specified in
Section 4.3 of [RFC8877]. For the reader's convenience this
format is illustrated in Figure 2.
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 2: IEEE 1588 Truncated Timestamp Format [IEEE1588].
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o NTP [RFC5905] 64-bit Timestamp Format: this format is specified in
Section 4.4 of [RFC8877]. For the reader's convenience this
format is illustrated in Figure 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 3: NTP [RFC5905] 64-bit Timestamp Format
Synchronization aspects of the timestamp format in the context of the
NSH timestamp allocation are discussed in Section 5.
4. Timestamping Use Cases
4.1. Network Analytics
Per-packet timestamping enables coarse-grained monitoring of the
network delay along the Service Function Chain. Once a potential
problem or bottleneck is detected, for example when the delay exceeds
a certain policy, a highly-granular hop-by-hop monitoring mechanism,
such as [RFC8592] or [I-D.ietf-ippm-ioam-data], can be triggered,
allowing to analyze and localize the problem.
Timestamping is also useful for logging, troubleshooting and for flow
analytics. It is often useful to maintain the timestamp of the first
and last packet of the flow. Furthermore, traffic mirroring and
sampling often requires a timestamp to be attached to analyzed
packets. Attaching the timestamp to the NSH provides an in-band
common time reference that can be used for various network analytics
applications.
4.2. Alternate Marking
A possible approach for passive performance monitoring is to use an
alternate marking method [RFC8321]. This method requires data
packets to carry a field that marks (colors) the traffic, and enables
passive measurement of packet loss, delay, and delay variation. The
value of this marking field is periodically toggled between two
values.
When the timestamp is incorporated in the NSH, it can natively be
used for alternate marking. For example, the least significant bit
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of the timestamp Seconds field can be used for this purpose, since
the value of this bit is inherently toggled every second.
4.3. Consistent Updates
The timestamp can be used for taking policy decisions such as
'Perform action A if timestamp>=T_0'. This can be used for enforcing
time-of-day policies or periodic policies in service functions.
Furthermore, timestamp-based policies can be used for enforcing
consistent network updates, as discussed in [DPT]. It should be
noted that, as in the case of Alternate Marking, this use case alone
does not require a full 64-bit timestamp, but could be implemented
with a significantly smaller number of bits.
5. Synchronization Considerations
Some of the applications that make use of the timestamp require the
Classifier and SFs to be synchronized to a common time reference, for
example using the Network Time Protocol [RFC5905] or the Precision
Time Protocol [IEEE1588]. Although it is not a requirement to use a
clock synchronization mechanism, it is expected that depending on the
applications that use the timestamp, such synchronization mechanisms
will be used in most deployments that use the timestamp allocation.
6. IANA Considerations
This memo includes no request to IANA.
7. Security Considerations
The security considerations of NSH in general are discussed in
[RFC8300]. NSH is typically run within a confined trust domain.
However, if a trust domain is not enough to provide the operator with
the protection against the timestamp threats described below, then
the operator SHOULD use transport-level protection between SFC
processing nodes as described in [RFC8300].
The security considerations of in-band timestamping in the context of
NSH is discussed in [RFC8592], and the current section is based on
that discussion.
The use of in-band timestamping, as defined in this document, can be
used as a means for network reconnaissance. By passively
eavesdropping to timestamped traffic, an attacker can gather
information about network delays and performance bottlenecks. A man-
in-the-middle attacker can maliciously modify timestamps in order to
attack applications that use the timestamp values, such as
performance monitoring applications.
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Since the timestamping mechanism relies on an underlying time
synchronization protocol, by attacking the time protocol an attack
can potentially compromise the integrity of the NSH timestamp. A
detailed discussion about the threats against time protocols and how
to mitigate them is presented in [RFC7384].
8. Acknowledgments
The authors thank Mohamed Boucadair and Greg Mirsky for their
thorough reviews and detailed comments.
9. References
9.1. 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>.
[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665,
DOI 10.17487/RFC7665, October 2015,
<https://www.rfc-editor.org/info/rfc7665>.
[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/info/rfc8174>.
[RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
"Network Service Header (NSH)", RFC 8300,
DOI 10.17487/RFC8300, January 2018,
<https://www.rfc-editor.org/info/rfc8300>.
[RFC8877] Mizrahi, T., Fabini, J., and A. Morton, "Guidelines for
Defining Packet Timestamps", RFC 8877,
DOI 10.17487/RFC8877, September 2020,
<https://www.rfc-editor.org/info/rfc8877>.
9.2. Informative References
[DPT] Mizrahi, T., Moses, Y., "The Case for Data Plane
Timestamping in SDN", IEEE INFOCOM Workshop on Software-
Driven Flexible and Agile Networking (SWFAN), 2016.
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[I-D.ietf-ippm-ioam-data]
Brockners, F., Bhandari, S., and T. Mizrahi, "Data Fields
for In-situ OAM", draft-ietf-ippm-ioam-data-12 (work in
progress), February 2021.
[I-D.ietf-sfc-nsh-broadband-allocation]
Napper, J., Kumar, S., Muley, P., Hendericks, W., and M.
Boucadair, "NSH Context Header Allocation for Broadband",
draft-ietf-sfc-nsh-broadband-allocation-01 (work in
progress), June 2018.
[I-D.ietf-sfc-nsh-dc-allocation]
Guichard, J., Smith, M., Kumar, S., Majee, S., and T.
Mizrahi, "Network Service Header (NSH) MD Type 1: Context
Header Allocation (Data Center)", draft-ietf-sfc-nsh-dc-
allocation-02 (work in progress), September 2018.
[IEEE1588]
IEEE, "IEEE 1588 Standard for a Precision Clock
Synchronization Protocol for Networked Measurement and
Control Systems Version 2", 2008.
[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>.
[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>.
[RFC8321] Fioccola, G., Ed., Capello, A., Cociglio, M., Castaldelli,
L., Chen, M., Zheng, L., Mirsky, G., and T. Mizrahi,
"Alternate-Marking Method for Passive and Hybrid
Performance Monitoring", RFC 8321, DOI 10.17487/RFC8321,
January 2018, <https://www.rfc-editor.org/info/rfc8321>.
[RFC8592] Browne, R., Chilikin, A., and T. Mizrahi, "Key Performance
Indicator (KPI) Stamping for the Network Service Header
(NSH)", RFC 8592, DOI 10.17487/RFC8592, May 2019,
<https://www.rfc-editor.org/info/rfc8592>.
Authors' Addresses
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Tal Mizrahi
Huawei
Israel
Email: tal.mizrahi.phd@gmail.com
Ilan Yerushalmi
Marvell
6 Hamada
Yokneam 2066721
Israel
Email: yilan@marvell.com
David Melman
Marvell
6 Hamada
Yokneam 2066721
Israel
Email: davidme@marvell.com
Rory Browne
Intel
Dromore House
Shannon, Co.Clare
Ireland
Email: rory.browne@intel.com
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