OPSAWG Y. Liu
Internet-Draft ZTE
Intended status: Standards Track Z. Li
Expires: 4 September 2025 Y. Liu
China Mobile
C. Lin
New H3C Technologies
3 March 2025
Export of Path Segment Identifier Information in IPFIX
draft-liu-opsawg-ipfix-path-segment-01
Abstract
This document introduces a new IPFIX Information Element to identify
the Path Segment Identifier(PSID) in the SRH for SRv6 path
identification purpose.
Status of This Memo
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This Internet-Draft will expire on 4 September 2025.
Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
4. Operational Considerations . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1. Normative References . . . . . . . . . . . . . . . . . . 5
6.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
[RFC9487] introduces new IP Flow Information Export (IPFIX)
Information Elements (IEs) to identify a set of information related
to Segment Routing over IPv6 (SRv6). For the SRv6 segment list, two
IPFIX IPv6 SRH IEs are defined in [RFC9487], srhSegmentIPv6BasicList
(elementID:496) and srhSegmentIPv6ListSection (elementID:497), both
encoding the Segment List in the SRH starting from Segment List[0].
When monitoring a traffic flow in an SR network, a typical use case
is to answer the following questions:
* How many packets are steered into an certain SR path ?
* Which SR Policy or candidate path or segment list this SR path
belongs to ?
To answer these questions, when exporting the flow record using IPFIX
messages, the SR path information needs to be included.
An SRv6 path could be identified by the content of a segment list in
IPFIX using IE496 or IE497, but the segment list is not always the
best key identifier due to the following reasons:
* When a segment list contains many SIDs, the size of IPFIX message
(especially the data record) would be large, making the collecting
and analyzing of flow records inefficient.
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* In the cases that different SRv6 policies use the same segment
list for traffic steering, it is difficult to distinguish the
traffic flow of different SRv6 policies.
* An SRv6 path may not be identified by the segment list carried by
the SRH in reduced mode [RFC8754] as the first SID is not present
in the SRH.
Path Segment is a type of Segment Routing (SR) segment, and a Path
Segment Identifier (PSID) is used to identify an SR path. PSID in
SRv6 networks is defined in [I-D.ietf-spring-srv6-path-segment]. In
SRH, the PSID appears as the last entry in the segment list.
This document introduces a new IPFIX Information Element to identify
the Path Segment Identifier(PSID) in the SRH for SRv6 path
identification purpose.
2. Terminology
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.
This document makes use of the terms defined in [RFC7011], [RFC8402],
and [RFC8754].
The following terms are used as defined in [RFC7011]:
* IPFIX
* IPFIX Information Elements
* Metering Process
* Template Record
* Data Record
* Collector
The following terms are used as defined in [RFC8402]:
* Segment Routing (SR)
* Segment List
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* SRv6
The following terms are used as defined in [RFC8754]:
* SRH
* Last Entry
3. IANA Considerations
This document requests IANA to create one new IE under the "IPFIX
Information Elements" registry [RFC7012] available at [IANA-IPFIX].
+-------+--------------------------------+
|Element| Name |
| ID | |
+-------+--------------------------------+
| TBD1 | srhPSID |
+-------+--------------------------------+
ElementID: TBD1
Name: srhPSID
Abstract Data Type: ipv6Address
Data Type Semantics: default
Description: The 128-bit IPv6 address that represents an SRv6 PSID.
Additional Information: Specified in Section 3 of
[I-D.ietf-spring-srv6-path-segment].
Reference: This document
4. Operational Considerations
As specified in [I-D.ietf-spring-srv6-path-segment], the P-flag in
the SRH is set to indicate the presence of PSID. In order to
generate Flow Records with PSID included, the metering process MUST
understand the P-flag. Only when the P-flag is set SHOULD the
metering process capture the last entry in the SRH to get the PSID.
If the P-flag in the packet is unset, when the srhPSID appears in the
template record, the corresponding field in the data record is
RECOMMENDED to set to all zero.
After decoding the IPFIX messages to get the flow record with PSID
included in it at the collector, the collector might process the flow
record locally or send it to an analyzer for further analysis
purpose. In order to recognize the SR path, the analysis node SHOULD
be aware of which SR path the PSID identifies. How to get this
information the is out of the scope of this document.
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The IE srhPSID can be used together with srhSegmentIPv6BasicList or
srhSegmentIPv6ListSection. As in [I-D.ietf-spring-srv6-path-segment]
section 3, the PSID allocate metering is depending on the use case,
including:
* each segment list may have its own PSID with different value;
* the same PSID may be used for some or all the segment list under a
Candidate path;
* the same PSID may be used for some or all Candidate Path within an
SRv6 policy.
So if srhPSID and srhSegmentIPv6BasicList/
srhSegmentIPv6ListSection appear together, the srhPSID MAY be used to
identify an SR Policy or candidate path, and the information carried
in srhSegmentIPv6BasicList/srhSegmentIPv6ListSection shows the
detailed segment list belonging to this SR Policy or candidate path.
This document does not limit how to use srhPSID and the detail is out
of scope.
5. Security Considerations
There are no additional security considerations regarding allocation
of these new IPFIX IEs compared to [RFC7012].
Other security considerations for SRv6 PSID described in
[I-D.ietf-spring-srv6-path-segment] apply to this document.
6. References
6.1. Normative References
[I-D.ietf-spring-srv6-path-segment]
Li, C., Cheng, W., Chen, M., Dhody, D., and Y. Zhu, "Path
Segment Identifier (PSID) in SRv6 (Segment Routing in
IPv6)", Work in Progress, Internet-Draft, draft-ietf-
spring-srv6-path-segment-11, 18 September 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
srv6-path-segment-11>.
[IANA-IPFIX]
IANA, "IP Flow Information Export (IPFIX) Entities",
<https://www.iana.org/assignments/ipfix>.
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[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>.
[RFC7011] Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
"Specification of the IP Flow Information Export (IPFIX)
Protocol for the Exchange of Flow Information", STD 77,
RFC 7011, DOI 10.17487/RFC7011, September 2013,
<https://www.rfc-editor.org/info/rfc7011>.
[RFC7012] Claise, B., Ed. and B. Trammell, Ed., "Information Model
for IP Flow Information Export (IPFIX)", RFC 7012,
DOI 10.17487/RFC7012, September 2013,
<https://www.rfc-editor.org/info/rfc7012>.
[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>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[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>.
6.2. Informative References
[RFC9487] Graf, T., Claise, B., and P. Francois, "Export of Segment
Routing over IPv6 Information in IP Flow Information
Export (IPFIX)", RFC 9487, DOI 10.17487/RFC9487, November
2023, <https://www.rfc-editor.org/info/rfc9487>.
Authors' Addresses
Yao Liu
ZTE
Nanjing
China
Email: liu.yao71@zte.com.cn
Zhenqiang Li
China Mobile
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Email: lizhenqiang@chinamobile.com
Yisong Liu
China Mobile
Email: liuyisong@chinamobile.com
Changwang Lin
New H3C Technologies
Email: linchangwang.04414@h3c.com
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