Internet DRAFT - draft-song-6man-srv6-pbt
draft-song-6man-srv6-pbt
6man H. Song, Ed.
Internet-Draft Futurewei Technologies
Intended status: Standards Track October 14, 2019
Expires: April 16, 2020
Support Postcard-Based Telemetry for SRv6 OAM
draft-song-6man-srv6-pbt-01
Abstract
Applications such as SRv6 TE may require to collect detailed
performance data on SR paths. Existing in-situ OAM techniques incur
encapsulation and header overhead issues. This document describes a
method based on Postcard-based Telemetry with Packet Marking for SRv6
on-path OAM, which avoids the extra overhead for encapsulating
telemetry-related instruction and metadata in SRv6 packets.
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
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This Internet-Draft will expire on April 16, 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. PBT Triggered by Marking for SRv6 . . . . . . . . . . . . . . 3
2.1. Data Template . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Postcard Correlation . . . . . . . . . . . . . . . . . . 4
2.3. Operational Considerations . . . . . . . . . . . . . . . 4
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
The ability to collect the on-path data about SRv6 packets at each
segment is important for SRv6 OAM, especially for monitoring the
application-aware services. Some SR-TE algorithms need to acquire
realtime flow forwarding performance on each path. The In-situ OAM
(IOAM) [I-D.ietf-ippm-ioam-data] trace option can be used for such
purpose. However, SRv6's SRH can be large due to the long segment
list. The IOAM trace option introduces significant additional
overhead to the SRv6 packets with its instruction and data trace.
The large header overhead complicates the packet processing and may
exceed the forwarding hardware's header processing capability.
The extra IOAM trace option header also brings encapsulation
challenges as documented in [I-D.li-6man-ipv6-sfc-ifit]. Here we
only restate a subtle issue about the IOAM scope: if IOAM header is
encapsulated as another IPv6 extension header, the juxtaposition of
IOAM and SRH makes it ambiguous to determine the scope and coverage
of IOAM: it is unclear if the IOAM is applied to the entire
forwarding path or just to the segment nodes. In reality, either
case can find its application.
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The Direct EXport (DEX) option of IOAM described in
[I-D.ioamteam-ippm-ioam-direct-export] partially relieves the packet
overhead pressure by avoiding including trace data in SRv6 packet,
but the encapsulation issue remains, so does the aforementioned
ambiguirty. In this document, we propose to apply the PBT-M scheme
from [I-D.song-ippm-postcard-based-telemetry] for on-path SRv6
telemetry, which can help to solve the encapsulation and overhead
issues.
2. PBT Triggered by Marking for SRv6
PBT-M requires marking a packet as a trigger to collect on-path data
about the packet. The collected data are exported by an independent
"postcard" packet. Therefore, there is no new header encapsulation
requirement.
Eight flag bits are currently reserved in SRH. One of those bits can
be used as the marking flag, as shown in the following figure. If
the "T"-bit is set to 1, the segment node which process the SRH needs
to export the on-path data about this packet as pre-configured
through management interface.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Routing Type | Segments Left |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Entry |T| Flags | Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
~ Segment List[] & TLV ~
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: SRH with PBT Mark Flag
2.1. Data Template
It is possible to have the same configuration for all the segment
nodes on the data set to collect. However, different flows may
require different data collection profiles. It would be more
flexible to have multiple different data templates supported by the
segment nodes and each packet can designate one template that best
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suits its interests to use. The template ID can be carried as a TLV
in SRH.
2.2. Postcard Correlation
As discussed in [I-D.song-ippm-postcard-based-telemetry], PBT-M has
some issues to correlate the postcards from the different segment
nodes for the same user packet. While several solutions are given to
mitigate the problem, it is ideal to be able to correlate the
postcards without any constraint and precondition.
A flow ID and a sequence number can be included as TLVs in SRH. The
format and usage of the flow ID and the sequence number are the same
as those in IOAM DEX option in
[I-D.ioamteam-ippm-ioam-direct-export]. Further, the exported
postcard may include the SRH or the current SID which provides a
trace to order the postcards.
2.3. Operational Considerations
The SR source node is responsible to determine the policy for setting
or resetting the "T"-bit.
A segment node can decide independently whether or not to react on
the "T"-bit.
3. Use Cases
TBD.
4. Security Considerations
Since PBT incurs some extra packet processing and transport cost, "T"
flag is usually selectively set on a subset of packets by the source
node. A potential DoS attack may set the "T" flag for all the packet
with the intention to overwhelm the segment nodes. Therefore, the
postcards should be generated on the basis of the best effort.
5. IANA Considerations
[I-D.ietf-6man-segment-routing-header] defines a new registry named
"Segment Routing Header Flags". This document requests the
allocation of a new flag bit "T" for the telemetry trigger mark.
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6. Contributors
TBD.
7. Acknowledgments
TBD.
8. References
8.1. 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>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[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>.
8.2. Informative References
[I-D.ietf-6man-segment-routing-header]
Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
Matsushima, S., and d. daniel.voyer@bell.ca, "IPv6 Segment
Routing Header (SRH)", draft-ietf-6man-segment-routing-
header-24 (work in progress), October 2019.
[I-D.ietf-ippm-ioam-data]
Brockners, F., Bhandari, S., Pignataro, C., Gredler, H.,
Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov,
P., Chang, R., daniel.bernier@bell.ca, d., and J. Lemon,
"Data Fields for In-situ OAM", draft-ietf-ippm-ioam-
data-07 (work in progress), September 2019.
[I-D.ioamteam-ippm-ioam-direct-export]
Song, H., Gafni, B., Zhou, T., Li, Z., Brockners, F.,
Bhandari, S., Sivakolundu, R., and T. Mizrahi, "In-situ
OAM Direct Exporting", draft-ioamteam-ippm-ioam-direct-
export-00 (work in progress), October 2019.
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[I-D.li-6man-ipv6-sfc-ifit]
Li, Z., Peng, S., and K. LEE, "IPv6 Encapsulation for SFC
and IFIT", draft-li-6man-ipv6-sfc-ifit-02 (work in
progress), September 2019.
[I-D.song-ippm-postcard-based-telemetry]
Song, H., Zhou, T., Li, Z., Shin, J., and K. Lee,
"Postcard-based On-Path Flow Data Telemetry", draft-song-
ippm-postcard-based-telemetry-05 (work in progress),
September 2019.
Author's Address
Haoyu Song (editor)
Futurewei Technologies
2330 Central Expressway
Santa Clara
USA
Email: hsong@futurewei.com
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