Internet Engineering Task Force (IETF) W. Cheng, Ed.
Request for Comments: 9714 China Mobile
Category: Standards Track X. Min, Ed.
ISSN: 2070-1721 ZTE Corp.
T. Zhou
Huawei
J. Dai
FiberHome
Y. Peleg
Broadcom
January 2025
Encapsulation for MPLS Performance Measurement with the Alternate-
Marking Method
Abstract
This document defines the encapsulation for MPLS performance
measurement with the Alternate-Marking Method, which performs flow-
based packet loss, delay, and jitter measurements on MPLS traffic.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9714.
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. Conventions Used in This Document
2.1. Abbreviations
2.2. Requirements Language
3. Flow-Based PM Encapsulation in MPLS
3.1. Examples for Applying Flow-ID Label in a Label Stack
3.1.1. Layout of the Flow-ID Label when Applied to MPLS
Transport
3.1.2. Layout of the Flow-ID Label when Applied to MPLS
Service
3.1.3. Layout of the Flow-ID Label when Applied to both MPLS
Transport and MPLS Service
4. Procedures of Encapsulation, Look-Up, and Decapsulation
5. Procedures of Flow-ID Allocation
6. FLC and FRLD Considerations
7. Equal-Cost Multipath Considerations
8. Security Considerations
9. IANA Considerations
10. References
10.1. Normative References
10.2. Informative References
Acknowledgements
Contributors
Authors' Addresses
1. Introduction
[RFC9341] describes a performance measurement method, which can be
used to measure packet loss, delay, and jitter on data traffic.
Since this method is based on marking consecutive batches of packets,
it is referred to as the Alternate-Marking Method. [RFC8372]
outlines key considerations for developing a solution for MPLS flow
identification, intended for use in performance monitoring of MPLS
flows.
This document defines the encapsulation for MPLS performance
measurement with the Alternate-Marking Method, which performs flow-
based packet loss, delay, and jitter measurements on the MPLS
traffic. The encapsulation defined in this document supports
performance monitoring at the intermediate nodes and MPLS flow
identification at both transport and service layers.
Note that in parallel to the work of this document, there is ongoing
work on MPLS Network Actions (MNA) [RFC9613]. The MPLS performance
measurement with the Alternate-Marking Method can also be achieved by
MNA encapsulation. In addition, MNA will provide a broader use-case
applicability. That means the MNA encapsulation is expected to
provide a more advanced solution. Once published as an RFC, it is
agreed that this document will be made Historic.
2. Conventions Used in This Document
2.1. Abbreviations
ACL: Access Control List
BoS: Bottom of Stack
cSPL: Composite Special Purpose Label, the combination of the
Extension Label (value 15) and an Extended Special Purpose Label
DSCP: Differentiated Services Code Point
ELC: Entropy Label Capability
ERLD: Entropy Readable Label Depth
eSPL: Extended Special Purpose Label, a special-purpose label that
is placed in the label stack after the Extension Label (value 15)
FL: Flow-ID Label
FLC: Flow-ID Label Capability
FLI: Flow-ID Label Indicator
FRLD: Flow-ID Readable Label Depth
IPFIX: IP Flow Information Export [RFC7011]
LSP: Label Switched Path
LSR: Label Switching Router
MPLS: Multi-Protocol Label Switching
NMS: Network Management System
PHP: Penultimate Hop Popping
PM: Performance Measurement
PW: PseudoWire
SFL: Synonymous Flow Label
SID: Segment ID
SR: Segment Routing
TC: Traffic Class
TTL: Time to Live
VC: Virtual Channel
VPN: Virtual Private Network
XL: Extension Label
2.2. 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.
3. Flow-Based PM Encapsulation in MPLS
This document defines the Flow-based MPLS performance measurement
encapsulation with the Alternate-Marking Method, as shown in
Figure 1.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extension Label (15) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flow-ID Label Indicator (18) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flow-ID Label |L|D|T|S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Flow-based PM Encapsulation in MPLS
The Flow-ID Label Indicator (FLI) is an Extended Special Purpose
Label (eSPL), which is combined with the Extension Label (XL, value
15) to form a Composite Special Purpose Label (cSPL), as defined in
[RFC9017]. The FLI is defined in this document as value 18.
The Traffic Class (TC) and Time To Live (TTL) fields of the XL and
FLI MUST use the same values of the label immediately preceding the
XL. The Bottom of the Stack (BoS) bit [RFC3032] for the XL and FLI
MUST be zero. If any XL or FLI processed by a node has the BoS bit
set, the node MUST discard the packet and MAY log an error.
The Flow-ID Label (FL) is used as an MPLS flow identification
[RFC8372]. Its value MUST be unique within the administrative
domain. The FL values MAY be allocated by an external NMS or
controller based on the measurement object instances (such as LSP or
PW). There is a one-to-one mapping between a Flow-ID and a flow.
The specific method on how to allocate the FL values is described in
Section 5.
The FL, preceded by a cSPL, can be placed either at the bottom or in
the middle, but not at the top, of the MPLS label stack, and it MAY
appear multiple times within a label stack. Section 3.1 of this
document provides several examples to illustrate the application of
FL in a label stack. The TTL for the FL MUST be zero to ensure that
it is not used inadvertently for forwarding. The BoS bit for the FL
depends on whether the FL is placed at the bottom of the MPLS label
stack, i.e., the BoS bit for the FL is set only when the FL is placed
at the bottom of the MPLS label stack.
Besides the flow identification, a color-marking field is also
necessary for the Alternate-Marking Method. To color the MPLS
traffic and to distinguish between hop-by-hop measurement and edge-
to-edge measurement, the TC for the FL is defined as follows:
* L(oss) bit is used for coloring the MPLS packets for loss
measurement. Setting the bit means color 1, and unsetting the bit
means color 0.
* D(elay) bit is used for coloring the MPLS packets for delay/jitter
measurement. Setting the bit means color for delay measurement.
* T(ype) bit is used to indicate the measurement type. When the T
bit is set to 1, that means edge-to-edge performance measurement.
When the T bit is set to 0, that means hop-by-hop performance
measurement.
Considering the FL is not used as a forwarding label, the repurposing
of the TC for the FL is feasible and viable.
3.1. Examples for Applying Flow-ID Label in a Label Stack
Three examples of different layouts of the FL (4 octets) are
illustrated as follows. Note that more examples may exist.
3.1.1. Layout of the Flow-ID Label when Applied to MPLS Transport
+----------------------+
| LSP |
| Label |
+----------------------+ <--+
| Extension | |
| Label | |
+----------------------+ |--- cSPL
| Flow-ID Label | |
| Indicator | |
+----------------------+ <--+
| Flow-ID |
| Label |
+----------------------+
| Application |
| Label |
+----------------------+ <= Bottom of stack
| |
| Payload |
| |
+----------------------+
Figure 2: Applying Flow-ID to MPLS Transport
With penultimate hop popping (PHP Section 3.16 of [RFC3031]), the top
label is "popped at the penultimate LSR of the LSP, rather than at
the LSP Egress". The final bullet of Section 4 of the present
document requires that "[t]he processing node MUST pop the XL, FLI,
and FL from the MPLS label stack when it needs to pop the preceding
forwarding label", which implies that the penultimate Label Switching
Router (LSR) needs to follow the requirement of Section 4 in order to
support this specification. If this is done, the egress LSR is
excluded from the performance measurement. Therefore, when this
specification is in use, PHP should be disabled, unless the
penultimate LSR is known to have the necessary support and unless
it's acceptable to exclude the egress LSR.
Also note that in other examples of applying Flow-ID to MPLS
transport, one LSP label can be substituted by multiple SID labels in
the case of using SR Policy, and the combination of cSPL and FL can
be placed between SID labels, as specified in Section 6.
3.1.2. Layout of the Flow-ID Label when Applied to MPLS Service
+----------------------+
| LSP |
| Label |
+----------------------+
| Application |
| Label |
+----------------------+ <--+
| Extension | |
| Label | |
+----------------------+ |--- cSPL
| Flow-ID Label | |
| Indicator | |
+----------------------+ <--+
| Flow-ID |
| Label |
+----------------------+ <= Bottom of stack
| |
| Payload |
| |
+----------------------+
Figure 3: Applying Flow-ID to MPLS Service
Note that in this case, the application label can be an MPLS PW
label, MPLS Ethernet VPN label, or MPLS IP VPN label, and it is also
called a VC label as defined in [RFC4026].
3.1.3. Layout of the Flow-ID Label when Applied to both MPLS Transport
and MPLS Service
+----------------------+
| LSP |
| Label |
+----------------------+ <--+
| Extension | |
| Label | |
+----------------------+ |--- cSPL
| Flow-ID Label | |
| Indicator | |
+----------------------+ <--+
| Flow-ID |
| Label |
+----------------------+
| Application |
| Label |
+----------------------+ <--+
| Extension | |
| Label | |
+----------------------+ |--- cSPL
| Flow-ID Label | |
| Indicator | |
+----------------------+ <--+
| Flow-ID |
| Label |
+----------------------+ <= Bottom of stack
| |
| Payload |
| |
+----------------------+
Figure 4: Applying Flow-ID to both MPLS Transport and MPLS Service
Note that for this example, the two FL values appearing in a label
stack must be different. In other words, the FL applied to the MPLS
transport and the FL applied to the MPLS service must be different.
Also, note that the two FL values are independent of each other. For
example, two packets can belong to the same VPN flow but different
LSP flows, or two packets can belong to different VPN flows but the
same LSP flow.
4. Procedures of Encapsulation, Look-Up, and Decapsulation
The procedures for FL encapsulation, look-up, and decapsulation are
summarized as follows:
* The MPLS ingress node [RFC3031] inserts the XL, FLI, and FL into
the MPLS label stack. At the same time, the ingress node sets the
FL value, the two color-marking bits, and the T bit, as defined in
Section 3.
* If edge-to-edge measurement is applied, i.e., the T bit is set to
1, then only the MPLS ingress/egress node [RFC3031] is the
processing node; otherwise, all the MPLS nodes along the LSP are
the processing nodes. The processing node looks up the FL with
the help of the XL and FLI, and exports the collected data (such
as the Flow-ID, block counters, and timestamps) to an external
NMS/controller, referring to the Alternate-Marking Method.
Section 6 of [ALT-MARK] describes protocols for collected data
export; the details on how to export the collected data are
outside the scope of this document. Note that while looking up
the FL, the transit node needs to inspect beyond the label at the
top of the label stack used to make forwarding decisions.
* The processing node MUST pop the XL, FLI, and FL from the MPLS
label stack when it needs to pop the preceding forwarding label.
The egress node MUST pop the whole MPLS label stack. This
document doesn't introduce any new process to the decapsulated
packet.
5. Procedures of Flow-ID Allocation
There are at least two ways of allocating Flow-ID. One way is to
allocate Flow-ID by a manual trigger from the network operator, and
the other way is to allocate Flow-ID by an automatic trigger from the
ingress node. Details are as follows:
* In the case of a manual trigger, the network operator manually
inputs the characteristics (e.g., IP five tuples and IP DSCP) of
the measured flow; then the NMS/controller generates one or two
Flow-IDs based on the input from the network operator and
provisions the ingress node with the characteristics of the
measured flow and the corresponding allocated Flow-ID(s).
* In the case of an automatic trigger, the ingress node identifies
the flow entering the measured path and exports the
characteristics of the identified flow to the NMS/controller by
IPFIX [RFC7011]; then the NMS/controller generates one or two
Flow-IDs based on the characteristics exported from the ingress
node and provisions the ingress node with the characteristics of
the identified flow and the corresponding allocated Flow-ID(s).
The policy preconfigured at the NMS/controller decides whether one
Flow-ID or two Flow-IDs are generated. If the performance
measurement on the MPLS service is enabled, then one Flow-ID applied
to the MPLS service is generated. If the performance measurement on
the MPLS transport is enabled, then one Flow-ID applied to the MPLS
transport is generated. If both of them are enabled, then two Flow-
IDs are respectively applied to the MPLS service and the MPLS
transport are generated. In this case, a transit node needs to look
up both of the two Flow-IDs by default. However, this behavior can
be changed through configuration, such as by setting it to look up
only the Flow-ID applied to the MPLS transport.
Whether using the two methods mentioned above or other methods to
allocate Flow-ID, the NMS/controller MUST ensure that every generated
Flow-ID is unique within the administrative domain and MUST NOT have
any value in the reserved label space (0-15) [RFC3032].
Specifically, the statement of "Flow-ID is unique" means that the
values of Flow-ID are distinct and non-redundant for any flow at any
given time within an administrative domain, such that no two flows
share the same Flow-ID. This uniqueness ensures that each flow can
be individually identified, tracked, and differentiated from others
for accurate performance monitoring and management.
6. FLC and FRLD Considerations
Analogous to the Entropy Label Capability (ELC) defined in Section 5
of [RFC6790] and the Entropy Readable Label Depth (ERLD) defined in
Section 4 of [RFC8662], the Flow-ID Label Capability (FLC) and the
Flow-ID Readable Label Depth (FRLD) are defined in this document.
Both FLC and FRLD have similar semantics with the ELC and ERLD to a
router, except that the Flow-ID is used in its flow identification
function while the Entropy is used in its load-balancing function.
The ingress node MUST insert each FL at an appropriate depth, which
ensures the node to which the FL is exposed has the FLC. The ingress
node SHOULD insert each FL within an appropriate FRLD, which is the
minimum FRLD of all the on-path nodes that need to read and use the
FL in question. How the ingress node knows the FLC and FRLD of all
the on-path nodes is outside the scope of this document.
When the SR paths are used for transport, the label stack grows as
the number of on-path segments increases. If the number of on-path
segments is high, that may become a challenge for the FL to be placed
within an appropriate FRLD. To overcome this potential challenge, an
implementation MAY allow the ingress node to place FL between SID
labels. This means that multiple identical FLs at different depths
MAY be interleaved with SID labels. When this occurs, sophisticated
network planning may be needed, which is beyond the scope of this
document.
7. Equal-Cost Multipath Considerations
Analogous to what's described in Section 5 of [RFC8957], under
conditions of equal-cost multipath, the introduction of the FL may
lead to the same problem that is caused by the Synonymous Flow Label
(SFL) [RFC8957]. The two solutions proposed for SFL also apply here.
Specifically, adding FL to an existing flow may cause that flow to
take a different path. If the operator expects to resolve this
problem, they can choose to apply entropy labels [RFC6790] or add FL
to all flows.
8. Security Considerations
As specified in Section 7.1 of [RFC9341], "for security reasons, the
Alternate-Marking Method MUST only be applied to controlled domains."
This requirement applies when the MPLS performance measurement with
Alternate-Marking Method is taken into account, which means the MPLS
encapsulation and related procedures defined in this document MUST
only be applied to controlled domains; otherwise, the potential
attacks discussed in Section 10 of [RFC9341] may be applied to the
deployed MPLS networks.
As specified in Section 3, the value of a an FL MUST be unique within
the administrative domain. In other words, the administrative domain
is the scope of an FL. The method for achieving multi-domain
performance measurement with the same FL is outside the scope of this
document. The FL MUST NOT be signaled and distributed outside the
administrative domain. Improper configuration that allows the FL to
be passed from one administrative domain to another would result in
Flow-ID conflicts.
To prevent packets carrying FLs from leaking from one domain to
another, domain boundary nodes MUST deploy policies (e.g., ACL) to
filter out these packets. Specifically, at the sending edge, the
domain boundary node MUST filter out the packets that carry the Flow-
ID Label Indicator FLI
and are sent to other domains. At the receiving edge, the domain
boundary node MUST drop the packets that carry the
Flow-ID Label Indicator FLI and are from
other domains. Note that packet leakage is neither breaching privacy
nor a source of DoS.
9. IANA Considerations
IANA has assigned the following value in the "Extended Special-
Purpose MPLS Label Values" registry within the "Special-Purpose
Multiprotocol Label Switching (MPLS) Label Values" registry group:
+=======+===============================+===========+
| Value | Description | Reference |
+=======+===============================+===========+
| 18 | Flow-ID Label Indicator (FLI) | RFC 9714 |
+-------+-------------------------------+-----------+
Table 1: New Extended Special-Purpose MPLS Label
Value for Flow-ID Label Indicator
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>.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001,
<https://www.rfc-editor.org/info/rfc3031>.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
[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>.
[RFC9017] Andersson, L., Kompella, K., and A. Farrel, "Special-
Purpose Label Terminology", RFC 9017,
DOI 10.17487/RFC9017, April 2021,
<https://www.rfc-editor.org/info/rfc9017>.
10.2. Informative References
[ALT-MARK] Fioccola, G., Zhu, K., Graf, T., Nilo, M., and L. Zhang,
"Alternate Marking Deployment Framework", Work in
Progress, Internet-Draft, draft-ietf-ippm-alt-mark-
deployment-02, 9 October 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-ippm-
alt-mark-deployment-02>.
[RFC4026] Andersson, L. and T. Madsen, "Provider Provisioned Virtual
Private Network (VPN) Terminology", RFC 4026,
DOI 10.17487/RFC4026, March 2005,
<https://www.rfc-editor.org/info/rfc4026>.
[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<https://www.rfc-editor.org/info/rfc6790>.
[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>.
[RFC8372] Bryant, S., Pignataro, C., Chen, M., Li, Z., and G.
Mirsky, "MPLS Flow Identification Considerations",
RFC 8372, DOI 10.17487/RFC8372, May 2018,
<https://www.rfc-editor.org/info/rfc8372>.
[RFC8662] Kini, S., Kompella, K., Sivabalan, S., Litkowski, S.,
Shakir, R., and J. Tantsura, "Entropy Label for Source
Packet Routing in Networking (SPRING) Tunnels", RFC 8662,
DOI 10.17487/RFC8662, December 2019,
<https://www.rfc-editor.org/info/rfc8662>.
[RFC8957] Bryant, S., Chen, M., Swallow, G., Sivabalan, S., and G.
Mirsky, "Synonymous Flow Label Framework", RFC 8957,
DOI 10.17487/RFC8957, January 2021,
<https://www.rfc-editor.org/info/rfc8957>.
[RFC9341] Fioccola, G., Ed., Cociglio, M., Mirsky, G., Mizrahi, T.,
and T. Zhou, "Alternate-Marking Method", RFC 9341,
DOI 10.17487/RFC9341, December 2022,
<https://www.rfc-editor.org/info/rfc9341>.
[RFC9613] Bocci, M., Ed., Bryant, S., and J. Drake, "Requirements
for Solutions that Support MPLS Network Actions (MNAs)",
RFC 9613, DOI 10.17487/RFC9613, August 2024,
<https://www.rfc-editor.org/info/rfc9613>.
Acknowledgements
The authors acknowledge Loa Andersson, Tarek Saad, Stewart Bryant,
Rakesh Gandhi, Greg Mirsky, Aihua Liu, Shuangping Zhan, Ming Ke, Wei
He, Ximing Dong, Darren Dukes, Tony Li, James Guichard, Daniele
Ceccarelli, Eric Vyncke, John Scudder, Gunter van de Velde, Roman
Danyliw, Warren Kumari, Murray Kucherawy, Deb Cooley, Zaheduzzaman
Sarker, and Deboraha Brungard for their careful review and very
helpful comments.
They also acknowledge Italo Busi and Chandrasekar Ramachandran for
their insightful MPLS-RT review and constructive comments.
Additionally, the authors thank Dhruv Dhody for the English grammar
review.
Contributors
Minxue Wang
China Mobile
Email: wangminxue@chinamobile.com
Wen Ye
China Mobile
Email: yewen@chinamobile.com
Authors' Addresses
Weiqiang Cheng (editor)
China Mobile
Beijing
China
Email: chengweiqiang@chinamobile.com
Xiao Min (editor)
ZTE Corp.
Nanjing
China
Email: xiao.min2@zte.com.cn
Tianran Zhou
Huawei
Beijing
China
Email: zhoutianran@huawei.com
Jinyou Dai
FiberHome
Wuhan
China
Email: djy@fiberhome.com
Yoav Peleg
Broadcom
United States of America
Email: yoav.peleg@broadcom.com