SRv6 In-situ Active Measurement
draft-song-spring-siam-05
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| Authors | Haoyu Song , Gyan Mishra , Tian Pan | ||
| Last updated | 2023-03-09 | ||
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draft-song-spring-siam-05
SPRING H. Song
Internet-Draft Futurewei Technologies
Intended status: Standards Track G. Mishra
Expires: 10 September 2023 Verizon Inc.
T. Pan
BUPT
9 March 2023
SRv6 In-situ Active Measurement
draft-song-spring-siam-05
Abstract
This draft describes an active measurement method for SRv6 which can
support segment-by-segment and end-to-end measurement on any SRv6
path using existing protocols such as IOAM. A packet containing an
SRH uses a flag bit to indicate the packet is an active probing
packet and requires segment-by-segment processing. The measurement
information, such as the IOAM header and data, is encapsulated in UDP
payload, indicated by a dedicated port number. The probing packet
originates from a segment source node, traverses an arbitrary segment
path, and terminates at a segment endpoint node, as configured by the
segment list in SRH. Each segment node on the path, when detecting
the flag, shall parse the UDP header and the payload. In the case of
IOAM, the node shall process the IOAM option conforming to the
standard procedures defined in the IOAM documents. The method is
compatible with some other SRv6 active measurement proposals and
support multiple applications.
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.
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
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 10 September 2023.
Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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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. An Active Measurement Framework for SRv6 . . . . . . . . . . 3
3. SRv6 In-Situ Active Measurement with IOAM . . . . . . . . . . 4
4. Network Operation . . . . . . . . . . . . . . . . . . . . . . 5
5. Applications . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Probing Packet Type Extension . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
SRv6 network OAM needs various means to collect data, detect issues,
and measure its performance. [RFC9259] provides some mechanisms for
SRv6 OAM. Some other general methods for performance measurement
such as [RFC8762] can also be applied for SRv6. However, these
methods have limited data coverage and measurement capability. More
mechanisms should be provided to enrich the OAM coverage.
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IOAM [RFC9197] can support extensible hop-by-hop data collection for
user traffic. It is beneficial for SRv6 network monitor and
measurement. Since it is designed for user-packet measurement,
[I-D.ali-spring-ioam-srv6] proposes to encapsulate IOAM in SRH TLV
options.
However, with its well-defined structure and functions, IOAM can also
be used for active measurement (i.e., in dedicated probing packets
without user payload) to fulfill many measurement tasks that are
inconvenient or infeasible to be applied on user traffic. For active
measurement, we can directly encapsulate the IOAM header and data in
the UDP-based probing packet payload. The similar method has been
proposed in [I-D.ietf-spring-stamp-srpm] to support STAMP for SRv6
measurement. IOAM is complement to STAMP by providing Segment-by-
Segment (SbS) measurement capability. The high-level method can be
generalized and extended to support other performance measurement
protocols under the same framework.
Fully built on exiting protocol components, the SR-based active
measurement method using IOAM can support some useful applications.
For example, it can be used to support network-wide telemetry
coverage by using pre-planned paths
[I-D.tian-bupt-inwt-mechanism-policy]; it can be used to actively
measure the backup paths for SRv6 traffic engineering; and by setting
the path end as the path head in SRH, it can naturally support two-
way or round-trip measurement.
2. An Active Measurement Framework for SRv6
As specified by [RFC8754], the Segment Routing Header (SRH) contains
an 8-bit "Flags" field. This document defines the following flag bit
'T' to designate the packet as a dedicated probing packet for
Segment-by Segment (SbS) active measurement.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| |T| |
+-+-+-+-+-+-+-+-+
Figure 1: A Hierarchical Edge Network
The O-bit defined in [I-D.ietf-6man-spring-srv6-oam] servers for user
traffic OAM, so the T-bit and O-bit are mutual exclusive. When T-bit
is set, O-bit must be cleared, and vice versa.
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Note that when applied for SRv6, the Edge-to-Edge (E2E) active
measurements, such as STAMP [I-D.ietf-spring-stamp-srpm] and IOAM E2E
option, do not need to set the T bit. The last segment endpoint node
will be required to parse and process the UDP payload of a probing
packet while the intermediate segment endpoint nodes simply forward
the packet.
The Next Header of SRH is set to UDP. A destination UDP port is
reserved to encode the type of the payload. For example, a port
number has been proposed to be reserved for STAMP in
[I-D.ietf-spring-stamp-srpm]. Similarly, another port number should
be reserved for IOAM trace option. If the destination port number
matches the reserved values, the UDP payload would encapsulate the
corresponding protocol header. The source UDP port can be used or
ignored depending on each use case. The UDP checksum processing
procedure conforms to [RFC6936].
3. SRv6 In-Situ Active Measurement with IOAM
We focus on a specific use case of the framework: using IOAM trace
option for segment-by-segment measurement. The IOAM header and data
format are specified in [RFC9197]. The complete active probing
packet format for IOAM is shown in Figure 2. The source UDP port can
be used as sequence number to track the probing packets on a specific
SR path.
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
|Ver (6)| Traffic Class | Flow Label | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Payload Length | NH : SRH | Hop Limit | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Source Address (128 bits) | RFC
| + 8200
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Destination Address (128 bits) | |
| | V
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| NH : UDP | Hdr Ext Len | Routing Type | Segments Left | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Last Entry | |1| Flags | Tag | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ RFC
| | 8754
| Segment List (m * 128 bits) | |
| | |
| | V
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| Source Port (TBD) | Destination Port (TBD) | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+RFC768
| Length | Checksum | V
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| Namespace-ID |NodeLen | Flags | RemainingLen| ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| IOAM-Trace-Type | Reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IOAM
| | |
| Node Data List (n * 32 bits) | |
| | |
| | V
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
Figure 2: The active probing packet format for IOAM trace option
4. Network Operation
To initiate an IOAM active measurement on a path, the probing packets
are generated at the SR source node. The source address is the
address of the SR source node and the destination address is the
address of first SR segment endpoint node. The SRH lists all the SR
segment endpoint nodes for which IOAM data will be collected.
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Each SR node on the path including the source node, when detecting
the T-flag, in addition to normal SRH processing, will further parse
the UDP header and IOAM header, and as directed by the IOAM header,
add data to the IOAM node data list.
The last SR segment endpoint node will terminate the probing packet.
The collected data can be exported according to the specifications
for IOAM data export.
If an SR segment endpoint node on the path is incapable of processing
the probing packet, it should ignore the T-flag and continue
forwarding the packet. The last SR segment endpoint node MUST be
able to process and terminate the probing packets.
5. Applications
This section summarizes a list of applications of the SRv6 In-situ
Active Measurement (SIAM) approach.
* The method can be used as an alternative way for applying IOAM on
user traffic in SRv6, because the forwarding behavior in SRv6
networks is determined by the SRH. As long as a probing packet
has the same SRH as the user packet, the data collected can
faithfully reflect the user packet's forwarding experience along
the same path. In this case, in order to collect the on-path data
for a specific flow, all we need is to copy the SRH from the flow
packet and construct the probing packets. The probing packet rate
can match the original flow or arbitrarily configured. The edge
of the SR domain must terminate the probing packets to avoid
leakage.
* To support SRv6 traffic engineering, some alternative paths may be
pre-computed. It is desirable to constantly measure the
performance of these paths so the best path can be picked when a
flow is swapped. Since each path can be represented by an SRH, we
can construct the probing packets with these SRHs to actively
measure their status and performance.
* In an SRv6 network, it is easy to conduct round trip measurement
by setting the starting node and the end node of a path to the
same segment source node, and setting the destination node as an
intermediate node on the path.
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* In order to detect or prevent gray network failures for SLA
guarantee, it is necessary to collect network-wide telemetry data
to gain full visibility within a SRv6 domain. We can apply the
algorithm described in [I-D.tian-bupt-inwt-mechanism-policy] to
calculate the minimum number of optimal SR paths to achieve the
full coverage, and construct probing packets on these paths.
6. Probing Packet Type Extension
The same framework can support other OAM protocols. In addition to
STAMP [I-D.ietf-spring-stamp-srpm], the active probing packets can
carry IOAM E2E option header and data [RFC9197], IOAM DEX option
header [RFC9326], and other OAM options. It is easy to use different
reserved UDP port numbers to differentiate the payload types.
7. Security Considerations
TBD
8. IANA Considerations
An SRH Flag bit 'T'. The bit position TBD
Optional UDP destination port numbers indicating different IOAM
options (TBD)
9. Acknowledgments
We acknowledge the comments and suggestions from Greg Mirsky and
Tianran Zhou which help to improve this document.
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>.
[RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement
for the Use of IPv6 UDP Datagrams with Zero Checksums",
RFC 6936, DOI 10.17487/RFC6936, April 2013,
<https://www.rfc-editor.org/info/rfc6936>.
[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>.
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[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[RFC9197] Brockners, F., Ed., Bhandari, S., Ed., and T. Mizrahi,
Ed., "Data Fields for In Situ Operations, Administration,
and Maintenance (IOAM)", RFC 9197, DOI 10.17487/RFC9197,
May 2022, <https://www.rfc-editor.org/info/rfc9197>.
[RFC9326] Song, H., Gafni, B., Brockners, F., Bhandari, S., and T.
Mizrahi, "In Situ Operations, Administration, and
Maintenance (IOAM) Direct Exporting", RFC 9326,
DOI 10.17487/RFC9326, November 2022,
<https://www.rfc-editor.org/info/rfc9326>.
10.2. Informative References
[I-D.ali-spring-ioam-srv6]
Ali, Z., Gandhi, R., Filsfils, C., Brockners, F., Nainar,
N. K., Pignataro, C., Li, C., Chen, M., and G. Dawra,
"Segment Routing Header encapsulation for In-situ OAM
Data", Work in Progress, Internet-Draft, draft-ali-spring-
ioam-srv6-06, 10 July 2022,
<https://datatracker.ietf.org/doc/html/draft-ali-spring-
ioam-srv6-06>.
[I-D.ietf-6man-spring-srv6-oam]
Ali, Z., Filsfils, C., Matsushima, S., Voyer, D., and M.
Chen, "Operations, Administration, and Maintenance (OAM)
in Segment Routing over IPv6 (SRv6)", Work in Progress,
Internet-Draft, draft-ietf-6man-spring-srv6-oam-13, 23
January 2022, <https://datatracker.ietf.org/doc/html/
draft-ietf-6man-spring-srv6-oam-13>.
[I-D.ietf-spring-stamp-srpm]
Gandhi, R., Filsfils, C., Voyer, D., Chen, M., Janssens,
B., and R. F. Foote, "Performance Measurement Using Simple
TWAMP (STAMP) for Segment Routing Networks", Work in
Progress, Internet-Draft, draft-ietf-spring-stamp-srpm-06,
26 February 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-spring-stamp-srpm-06>.
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[I-D.tian-bupt-inwt-mechanism-policy]
Pan, T., Gao, M., Song, E., Bian, Z., and X. Lin, "In-band
Network-Wide Telemetry", Work in Progress, Internet-Draft,
draft-tian-bupt-inwt-mechanism-policy-01, 25 October 2020,
<https://datatracker.ietf.org/doc/html/draft-tian-bupt-
inwt-mechanism-policy-01>.
[RFC8762] Mirsky, G., Jun, G., Nydell, H., and R. Foote, "Simple
Two-Way Active Measurement Protocol", RFC 8762,
DOI 10.17487/RFC8762, March 2020,
<https://www.rfc-editor.org/info/rfc8762>.
[RFC9259] Ali, Z., Filsfils, C., Matsushima, S., Voyer, D., and M.
Chen, "Operations, Administration, and Maintenance (OAM)
in Segment Routing over IPv6 (SRv6)", RFC 9259,
DOI 10.17487/RFC9259, June 2022,
<https://www.rfc-editor.org/info/rfc9259>.
Authors' Addresses
Haoyu Song
Futurewei Technologies
Santa Clara,
United States of America
Email: haoyu.song@futurewei.com
Gyan Mishra
Verizon Inc.
Email: gyan.s.mishra@verizon.com
Tian Pan
BUPT
Email: pan@bupt.edu.cn
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