SRv6 In-situ Active Measurement
draft-song-spring-siam-00
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| Authors | Haoyu Song , Tian Pan | ||
| Last updated | 2020-12-15 | ||
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draft-song-spring-siam-00
SPRING H. Song
Internet-Draft Futurewei Technologies
Intended status: Standards Track T. Pan
Expires: June 18, 2021 BUPT
December 15, 2020
SRv6 In-situ Active Measurement
draft-song-spring-siam-00
Abstract
This draft describes an in-band active measurement method for SRv6.
A probing packet contains an SRH with a flag bit set. The IOAM
header and data are encapsulated in UDP payload. The probing packet
originates from a segment source node and terminates at a configured
segment endpoint node. Each segment node on the path, when detecting
the flag, parses the UDP header and the IOAM header, and adds data to
the IOAM node data fields. Multiple applications can be supported by
the method.
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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 18, 2021.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. In-situ Active Measurement for SRv6 . . . . . . . . . . . . . 3
3. Network Operation . . . . . . . . . . . . . . . . . . . . . . 5
4. Applications . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Probing Packet Type Extension . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
To support SRv6 network operation, we need various means to collect
data and measure the performance of SRv6 network.
[I-D.ietf-6man-spring-srv6-oam] 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.
[I-D.ietf-ippm-ioam-data] supports extensible data collection for
user traffic. It is beneficial for SRv6 network monitor and
measurement. [I-D.ali-spring-ioam-srv6] proposes to encapsulate IOAM
in SRH TLV. However, IOAM's overhead may cause packet fragmentation
and its processing may affect the packet forwarding throughput.
Moreover, due to the extension header limitations asserted by
[RFC8200], it is not easy to come up with a scheme to encapsulate the
IOAM header and data in other locations in SRv6 user packets.
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Fortunately, the forwarding behavior in SRv6 networks is determined
by the SRH. The IOAM header and data do not need to be added to user
packets. Instead, they can be encapsulated in an independent packet.
As long as this packet has the same SRH as the user packet, the data
collected can faithfully reflect the user packet's forwarding
experience, so the result is similar to that by applying IOAM on SRv6
user packets. This approach retains the benefits of in-situ
measurement but avoids the aforementioned issues.
The IOAM header and data processing can be done in slow path, without
worrying about delaying the user traffic. Because of this, the
potential limitation of the forwarding hardware's header processing
capability (e.g., the hearder parsing depth) is no longer an issue.
This SR-based active measurement approach also supports some other
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.
The approach is built on existing protocol components with limited
extra requirements.
2. In-situ Active Measurement 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 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.
The Next Header of SRH is set to UDP. A destination UDP port is
reserved to further verify this packet is an active probing packet
and the UDP payload encapsulates the IOAM header and data as
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specified in [I-D.ietf-ippm-ioam-data]. The source UDP port can be
used as sequence number to track the probing packets on a specific SR
path.
The complete active probing packet format is shown in Figure 2.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
|Ver (6)| Traffic Class | Flow Label | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Payload Length | NH : SRH | Hop Limit | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Source Address (128 bits) | RFC8200
| + |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Destination Address (128 bits) | |
| | V
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| NH : UDP | Hdr Ext Len | Routing Type | Segments Left | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Last Entry | |1| Flags | Tag | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ RFC8754
| | |
| Segment List (m * 128 bits) | |
| | |
| | V
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| Source Port | 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
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3. Network Operation
The SR source node constructs the probing packets. 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.
Each SR node on the path, 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 and analyzed according to
configuration.
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.
4. Applications
This section summarizes a list of applications of the SRv6 In-situ
Active Measurement (SIAM) approach.
o As described in Section 1, this is an easy way to apply IOAM in
SRv6. 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.
o To support SRv6 traffic engineering, some alternative paths may be
pre-computed. It is desirable to 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.
o 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.
o To collect the network wide telemetry data and gain global
visibility within a SRv6 domain, we can apply the algorithm
described in [I-D.tian-bupt-inwt-mechanism-policy] to calculate
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the optimal SR paths, and construct probing packets on these
paths.
5. Probing Packet Type Extension
The same scheme is also suitable for other types of probing packets.
For example, The probing packets can carry IOAM E2E option header and
data, IOAM DEX option header, and other telemetry headers and data.
It is easy to use different reserved UDP port numbers to
differentiate the payload types.
6. Security Considerations
7. IANA Considerations
An SRH Flag bit 'T'. The bit position TBD
A optional UDP destination port number indicating IOAM payload (TBD)
8. Acknowledgments
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>.
[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>.
[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>.
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9.2. Informative References
[I-D.ali-spring-ioam-srv6]
Ali, Z., Gandhi, R., Filsfils, C., Brockners, F., Nainar,
N., Pignataro, C., Li, C., Chen, M., and G. Dawra,
"Segment Routing Header encapsulation for In-situ OAM
Data", draft-ali-spring-ioam-srv6-03 (work in progress),
November 2020.
[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 Networks with IPv6 Data plane (SRv6)",
draft-ietf-6man-spring-srv6-oam-08 (work in progress),
October 2020.
[I-D.ietf-ippm-ioam-data]
Brockners, F., Bhandari, S., and T. Mizrahi, "Data Fields
for In-situ OAM", draft-ietf-ippm-ioam-data-11 (work in
progress), November 2020.
[I-D.tian-bupt-inwt-mechanism-policy]
Pan, T., Gao, M., Song, E., Bian, Z., and X. Lin, "In-band
Network-Wide Telemetry", draft-tian-bupt-inwt-mechanism-
policy-01 (work in progress), October 2020.
[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>.
Authors' Addresses
Haoyu Song
Futurewei Technologies
Santa Clara
USA
Email: haoyu.song@futurewei.com
Tian Pan
BUPT
Beijing
China
Email: pan@bupt.edu.cn
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