Internet-Draft Encap for MPLS PM with AMM September 2024
Cheng, et al. Expires 16 March 2025 [Page]
Workgroup:
MPLS Working Group
Internet-Draft:
draft-ietf-mpls-inband-pm-encapsulation-18
Published:
Intended Status:
Standards Track
Expires:
Authors:
W. Cheng, Ed.
China Mobile
X. Min, Ed.
ZTE Corp.
T. Zhou
Huawei
J. Dai
FiberHome
Y. Peleg
Broadcom

Encapsulation For MPLS Performance Measurement with 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 the MPLS traffic.

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 working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 16 March 2025.

Table of Contents

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, when published as an RFC and it is agreed that this document will be made Historic at that time.

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

ECMP: Equal-Cost Multipath

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 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 (TBA1)    |  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 TBA1.

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 Flow-ID Label 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 Flow-ID Label 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 achieve the purpose of coloring 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:

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 Flow-ID label (4 octets) are illustrated as follows. Note that more examples may exist.

(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". Since Section 4 of the present document, final bullet, requires that "The processing node MUST pop the XL, FLI and FL from the MPLS label stack when it needs to pop the preceding forwarding label", this 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 would be 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 Flow-ID label can be placed between SID labels, as specified in Section 6.

(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) 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 Flow-ID Label values appearing in a label stack must be different. In other words, the Flow-ID label applied to the MPLS transport and the Flow-ID label applied to the MPLS service must be different. Also, note that the two Flow-ID label 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 Flow-ID label encapsulation, look-up and decapsulation are summarized as follows:

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:

The policy pre-configured at the NMS/controller decides whether one Flow-ID or two Flow-IDs would be generated. If the performance measurement on the MPLS service is enabled, then one Flow-ID applied to the MPLS service would be generated. If the performance measurement on the MPLS transport is enabled, then one Flow-ID applied to the MPLS transport would be generated. If both of them are enabled, then two Flow-IDs are respectively applied to the MPLS service and the MPLS transport would be generated. In this case, a transit node needs to look up both of the two Flow-IDs by default. However, this behaviour 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 (ECMP), the introduction of the FL may lead to the same problem as caused by the Synonymous Flow Label (SFL) [RFC8957]. The two solutions proposed for SFL would 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". That 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 Flow-ID label MUST be unique within the administrative domain. In other words, the administrative domain is the scope of a Flow-ID label. The method for achieving multi-domain performance measurement with the same Flow-ID label is outside the scope of this document. The Flow-ID label MUST NOT be signaled and distributed outside the administrative domain. Improper configuration that allows the Flow-ID label to be passed from one administrative domain to another would result in Flow-ID conflicts.

To prevent packets carrying Flow-ID labels 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 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 and are from other domains. Note that packet leakage is neither breaching privacy nor can be a source of DoS.

9. Implementation Status

[Note to the RFC Editor - remove this section before publication, as well as remove the reference to [RFC7942].

This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in [RFC7942]. The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist.

According to [RFC7942], "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. It is up to the individual working groups to use this information as they see fit".

9.1. Fiberhome

9.2. Huawei Technologies

9.3. ZTE Corp

9.4. China Mobile

China Mobile reported that they have conducted interconnection tests with multiple vendors according to this draft. The tests result have proven that the solutions from multiple vendors are mature and ready for large-scale deployment. This report was last updated on January 10, 2024.

10. IANA Considerations

From the "Extended Special-Purpose MPLS Label Values" registry in the "Special-Purpose Multiprotocol Label Switching (MPLS) Label Values" namespace, a new value for the Flow-ID Label Indicator is requested from IANA as follows:

Table 1: New Extended Special-Purpose MPLS Label Value for Flow-ID Label Indicator
Value Description Reference
TBA1 (value 18 is recommended) Flow-ID Label Indicator (FLI) This Document

11. Acknowledgements

The authors would like to 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 wish to acknowledge Italo Busi and Chandrasekar Ramachandran for their insightful MPLS-RT review and constructive comments.

Additionally, the authors would like to thank Dhruv Dhody for the English grammar review.

12. Contributors

Minxue Wang
China Mobile
Email: wangminxue@chinamobile.com

Wen Ye
China Mobile
Email: yewen@chinamobile.com

13. References

13.1. Normative References

[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <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, , <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, , <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, , <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, , <https://www.rfc-editor.org/info/rfc9017>.

13.2. Informative References

[I-D.ietf-ippm-alt-mark-deployment]
Fioccola, G., Keyi, Z., Graf, T., Nilo, M., and L. Zhang, "Alternate Marking Deployment Framework", Work in Progress, Internet-Draft, draft-ietf-ippm-alt-mark-deployment-01, , <https://datatracker.ietf.org/doc/html/draft-ietf-ippm-alt-mark-deployment-01>.
[RFC4026]
Andersson, L. and T. Madsen, "Provider Provisioned Virtual Private Network (VPN) Terminology", RFC 4026, DOI 10.17487/RFC4026, , <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, , <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, , <https://www.rfc-editor.org/info/rfc7011>.
[RFC7942]
Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: The Implementation Status Section", BCP 205, RFC 7942, DOI 10.17487/RFC7942, , <https://www.rfc-editor.org/info/rfc7942>.
[RFC8372]
Bryant, S., Pignataro, C., Chen, M., Li, Z., and G. Mirsky, "MPLS Flow Identification Considerations", RFC 8372, DOI 10.17487/RFC8372, , <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, , <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, , <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, , <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, , <https://www.rfc-editor.org/info/rfc9613>.

Authors' Addresses

Weiqiang Cheng (editor)
China Mobile
Beijing
China
Xiao Min (editor)
ZTE Corp.
Nanjing
China
Tianran Zhou
Huawei
Beijing
China
Jinyou Dai
FiberHome
Wuhan
China
Yoav Peleg
Broadcom
United States of America