| Internet-Draft | IPFIX for PSID | August 2026 |
| Liu, et al. | Expires 3 March 2027 | [Page] |
This document introduces new IPFIX Information Elements to identify the Segment Routing (SR) Path Segment Identifier (PSID) for SR-MPLS and SRv6 paths identification.¶
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When monitoring a traffic flow in an SR network, a typical use case is to answer the following questions:¶
To answer these questions, when exporting IPFIX flow records, the SR path information needs to be included. However, there are still some shortcomings with the existing mechanisms.¶
In SR-MPLS [RFC8660], a segment is encoded as an MPLS label. For MPLS label stack information collection, IPFIX IE mplsLabelStackSection (elementID:316) [RFC5477] can carry a series of n octets from the MPLS label stack of a sampled packet, which can be leveraged to carry the whole or part of the MPLS label stack. And IEs from mplsTopLabelStackSection, mplsLabelStackSection2, mplsLabelStackSection3 to mplsLabelStackSection10 (elementID from 70 to 79) [RFC5102] provide mechanism to carry the individual MPLS label information in the IPFIX message.¶
But the above IEs are not sufficient for SR-MPLS path identification:¶
[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].¶
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:¶
Path Segment is a type of Segment Routing (SR) segment, and a Path Segment Identifier (PSID) is used to identify an SR path.¶
For SR-MPLS, as specified in [RFC9545], a PSID is a single label that is assigned from the Segment Routing Local Block (SRLB) of the egress node of an SR path, and it immediately follows the last label of the SR path.¶
PSID for SRv6 networks is defined in [I-D.ietf-spring-srv6-path-segment]. In SRH, the PSID appears in the last entry in the segment list.¶
This document introduces new IPFIX Information Elements to identify the PSIDs for SR-MPLS and SRv6 paths identification.¶
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], [RFC8754] and [RFC9545].¶
The following terms are used as defined in [RFC7011]:¶
The following terms are used as defined in [RFC8402]:¶
The following terms are used as defined in [RFC8754]:¶
The following terms are used as defined in [RFC9545] and [I-D.ietf-spring-srv6-path-segment]:¶
A new IE "psidMplsLabelStackSection" is defined in this document to identify the SR-MPLS PSID, it carries an MPLS label that represents an SR-MPLS PSID, as well as the Exp, and S fields from the label stack entry that containing a PSID.¶
psidMplsLabelStackSection¶
TBD1¶
The Label (i.e., the MPLS PSID), Exp, and S fields from the label stack entry that contains a PSID. The size of this Information Element is 3 octets.¶
0 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label(PSID) | Exp |S| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+¶
Label: the MPLS PSID, 20 bits¶
Exp: Experimental Use, 3 bits¶
S: Bottom of Stack, 1 bit¶
octetArray¶
default¶
This document.¶
A new IE "srhPsidIPv6" is defined in this document to identify the PSID in the SRH, it carries a 128-bit value that represents an SRv6 PSID.¶
srhPsidIPv6¶
TBD2¶
The 128-bit value that represents an SRv6 PSID.¶
octetArray¶
default¶
Specified in Section 3 of [I-D.ietf-spring-srv6-path-segment].¶
This document.¶
Although IE srhPsidIPv6 is used to identify an SRv6 path, this document doesn't limit using srhPsidIPv6 together with srhSegmentIPv6BasicList or srhSegmentIPv6ListSection in the same IPFIX message, see Section 4.2 for more information.¶
Network Observability, as described in [RFC9940], is the process of enabling network behavioral assessment through analysis of observed operational network data, and Network Telemetry (e.g., IPFIX) is the basis of Network Observability.¶
PSID benefits the SR IPFIX flow visibility for Network Observability. As described in Section 3 of [RFC9545] and Section 2 of [I-D.ietf-spring-srv6-path-segment], SR-MPLS and SRv6 PSID may be used to identify an SR Path in use cases such as performance measurement, bi-directional path association, end-to-end path protection, etc. By carrying PSID information in IPFIX messages, SR path of the traffic flow can be easily identified in the above use cases.¶
To achieve operational visibility into SR networks, operators can leverage PSID information exported in IPFIX records in conjunction with the mapping between the PSID and the SR path context. This enables operational use cases such as:¶
The detailed procedures for correlating PSID with network events and diagnosing forwarding failures are deployment-specific and outside the scope of this document.¶
The association between the exported PSID value and the corresponding SR path context (SR Policy, Candidate Path, or Segment List) can be established by the controller and signaled via BGP [I-D.ietf-idr-sr-policy-path-segment] or PCEP [I-D.ietf-pce-sr-path-segment]. Alternatively, the association can be instantiated on the ingress/egress node of the path and reported to the controller via PCEP [I-D.ietf-pce-sr-path-segment] or BGP-LS [I-D.ietf-idr-bgp-ls-sr-policy-path-segment].¶
After decoding the IPFIX messages at the Collector, to get the flow record with the PSID, the Collector might process the flow record locally or send it to a data processing or analytics component. To recognize which SR path a PSID identifies, the analysis node needs to be aware of the association between the exported PSID value and the corresponding SR path context. This association can be obtained via the following methods:¶
The detailed procedures for obtaining and maintaining this mapping are outside the scope of this document.¶
The following clarifications apply to the behavior of PSID when the network path changes:¶
As specified in [RFC9545] and [I-D.ietf-spring-srv6-path-segment], the same PSID value may be used to identify a single segment list, multiple segment lists, some or all segment lists under a Candidate Path, or some or all Candidate Paths within an SR Policy, depending on the use case. This flexibility allows operators to aggregate traffic statistics at different granularities.¶
To avoid ambiguity in the exported PSID value, the entity (e.g., the controller, the ingress node, or the egress node of the path) that generates the association between the PSID and the SR path is responsible for ensuring that the exported PSID values are distinguishable within the intended scope (e.g., within a node, or the SR network domain). Reuse of the same PSID value outside its intended scope is undefined for correlation purposes.¶
The Collector can resolve the association between an exported PSID value and the corresponding SR path by consulting the mapping information obtained from the entity responsible for the mapping, as described in Section 4.1.1. The detailed procedures for obtaining and maintaining this mapping are outside the scope of this document.¶
To generate Flow Records with psidMplsLabelStackSection, the Metering Process needs to acquire the information of the corresponding PSID, i.e., which label is the PSID. This may be achieved by configuration or signaling. How to get this information is out of the scope of this document.¶
As specified in [I-D.ietf-spring-srv6-path-segment], the G-Flag in the SRH is set to indicate that the last entry of the Segment List contains a 128-bit metadata object as an opaque identifier or data payload defined by the specific application (e.g., a Path Segment Identifier). To generate Flow Records with PSID included, the Metering Process MUST understand the G-Flag. Only when the G-Flag is set and the last entry carries an SRv6 PSID SHOULD the Metering Process capture the last entry in the SRH to get the PSID. If the G-Flag in the packet is unset or the last entry does not carry an SRv6 PSID, the srhPsidIPv6 SHOULD NOT be used in the template. When the srhPsidIPv6 appears in a Data Record with G-Flag unset, it SHOULD be ignored.¶
As in [I-D.ietf-spring-srv6-path-segment] Section 3, the PSID allocation depends on the use cases, including:¶
If srhPsidIPv6 and srhSegmentIPv6BasicList/srhSegmentIPv6ListSection appear together, the srhPsidIPv6 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 srhPsidIPv6 and the detail is out of scope.¶
The export of PSID values in IPFIX records may reveal information about the SR path topology that is not exposed by standard 5-tuple flow records, including which SR paths exist and how traffic is distributed across them. An observer with access to the IPFIX data stream could potentially use this information to infer the SR network topology. Deployments should consider appropriate access controls for IPFIX data, as discussed in [RFC7011], to limit exposure of this information to authorized entities only. The security considerations of the underlying SR-MPLS PSID [RFC9545] and SRv6 PSID [I-D.ietf-spring-srv6-path-segment] also apply.¶
This document requests IANA to create new IEs under the "IPFIX Information Elements" registry [RFC7012] available at [IANA-IPFIX].¶
| Element ID | Name | Reference |
| TBD1 | psidMplsLabelStackSection | Section 3.1 |
| TBD2 | srhPsidIPv6 | Section 3.2 |
Thanks to Thomas Graf, Paul Aitken and Saumya Dikshit for their detailed review and comments. Thanks to Cheng Li and Chongfeng Xie for their helpful comments and suggestions.¶