Encapsulation For MPLS Performance Measurement with Alternate Marking Method

Abstract

This document defines the encapsulation for MPLS performance measurement with alternate marking method, which performs flow-based packet loss, delay, and jitter measurements on MPLS live traffic.¶

1. Introduction

[RFC9341] describes a performance measurement method, which can be used to measure packet loss, delay, and jitter on live traffic. Since this method is based on marking consecutive batches of packets, it's referred to as Alternate-Marking Method. [RFC8372] describes the desired capabilities for MPLS flow identification, intended for in-band performance monitoring of MPLS flows.¶

This document defines the encapsulation for MPLS performance measurement with alternate marking method, which performs flow-based packet loss, delay, and jitter measurements on MPLS live traffic. The encapsulation defined in this document supports performance monitoring at the intermediate nodes, as well as MPLS flow identification at both transport and service layers.¶

This document employs an encapsulation method, other than Synonymous Flow Label (SFL), to achieve MPLS flow identification. The method described in this document is complementary to the SFL method [RFC8957] [I-D.ietf-mpls-sfl-control], the former mainly aims at hop-by-hop processing and the latter mainly aims at edge-to-edge processing. Different sets of MPLS flows may use different methods.¶

The method described in this document is also complementary to the In-situ OAM method [RFC9197] [RFC9326], the former doesn't introduce any new header whereas the latter introduces a new In-situ OAM header. Furthermore, the former requires the network nodes to collect the data used for performance measurement, while the latter requires the network nodes to collect the data used for operational and telemetry information collection. An MPLS flow may apply both of the two methods concurrently.¶

2. Flow-based PM Encapsulation in MPLS

Flow-based MPLS performance measurement encapsulation with alternate marking method has the following format:¶

 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      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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) [RFC3032] for the XL and FLI SHOULD follow the same field values of that label immediately preceding the XL. Otherwise, the TC and TTL for the XL and FLI MAY be different values if it is known that the XL will not be exposed as the top label at any point along the LSP. The Bottom of Stack (BoS) bit [RFC3032] for the XL and FLI MUST be zero.¶

The Flow-ID Label (FL) is used as an MPLS flow identification [RFC8372], its value MUST be unique within the administrative domain. Flow-ID values can be allocated by an external NMS/controller, based on measurement object instance such as LSP or PW. There is a one-to-one mapping between Flow-ID and flow. The specific method on how to allocate the Flow-ID values is described in Section 4.¶

The FL can be placed at either the bottom or the middle of the MPLS label stack, and the FL MAY appear multiple times in a label stack. Section 2.1 of this document provides several examples to illustrate how to apply 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.¶

Besides the flow identification, a color-marking field is also necessary for alternate marking method. To achieve the purpose of coloring the MPLS traffic, as well as the distinction 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.¶
• D(elay) bit is used for coloring the MPLS packets for delay/jitter measurement.¶
• T(ype) bit is used to indicate the measurement type. When T bit is set to 1, that means edge-to-edge performance measurement. When T bit is set to 0, that means hop-by-hop performance measurement.¶

+----------------------+
|          LSP         |
|         Label        |
+----------------------+ <--+
|       Extension      |    |
|         Label        |    |
+----------------------+    |--- cSPL
|     Flow-ID Label    |    |
|       Indicator      |    |
+----------------------+ <--+
|        Flow-ID       |
|         Label        |
+----------------------+
|      Application     |
|         Label        |
+----------------------+ <= Bottom of stack
|                      |
|        Payload       |
|                      |
+----------------------+

+----------------------+
|          LSP         |
|         Label        |
+----------------------+
|      Application     |
|         Label        |
+----------------------+ <--+
|       Extension      |    |
|         Label        |    |
+----------------------+    |--- cSPL
|     Flow-ID Label    |    |
|       Indicator      |    |
+----------------------+ <--+
|        Flow-ID       |
|         Label        |
+----------------------+ <= Bottom of stack
|                      |
|        Payload       |
|                      |
+----------------------+

+----------------------+
|          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       |
|                      |
+----------------------+

3. Procedures of Encapsulation, Look-up and Decapsulation

The procedures for Flow-ID label encapsulation, look-up and decapsulation are summarized as follows:¶

• The ingress node inserts the XL, FLI and FL into the MPLS label stack. At the same time, the ingress node sets the Flow-ID value, the two color-marking bits and the T bit, as defined in Section 2.¶
• If the hop-by-hop measurement is applied, i.e., the T bit is set to 0, then whether the transit node or the egress node is the processing node. If the edge-to-edge measurement is applied, i.e., the T bit is set to 1, then only the egress node is the processing node. 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. Note that while looking up the Flow-ID label, the transit node needs to perform some deep packet inspection beyond the label (at the top of the label stack) used to take forwarding decisions.¶
• The processing node may also pop the XL, FLI and FL from the MPLS label stack. The egress node pops the whole MPLS label stack, and this document doesn't introduce any new process to the decapsulated packet.¶

4. Procedures of Flow-ID allocation

There are two ways of allocating Flow-ID, one way is to allocate Flow-ID by manual trigger from the network operator, and the other way is to allocate Flow-ID by automatic trigger from the ingress node. Details are as follows:¶

• In the case of manual trigger, the network operator would manually input the characteristics (e.g. IP five tuples and IP DSCP) of the measured flow, then the NMS/controller would generate one or two Flow-IDs based on the input from the network operator, and provision the ingress node with the characteristics of the measured flow and the corresponding allocated Flow-ID(s).¶
• In the case of automatic trigger, the ingress node would identify the flow entering the measured path, export the characteristics of the identified flow to the NMS/controller by IPFIX [RFC7011], then the NMS/controller would generate one or two Flow-IDs based on the characteristics exported from the ingress node, and provision the ingress node with the characteristics of the identified flow and the corresponding allocated Flow-ID(s).¶

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 MPLS service is enabled, then one Flow-ID applied to MPLS service would be generated; If the performance measurement on MPLS transport is enabled, then one Flow-ID applied to MPLS transport would be generated; If both of them are enabled, then two Flow-IDs respectively applied to MPLS service and MPLS transport would be generated, in this case, the transit node needs to look up both of the two Flow-IDs by default, and that can be changed by configuration to, e.g., look up only the Flow-ID applied to MPLS transport.¶

Whether using manual trigger or automatic trigger, the NMS/controller MUST guarantee every generated Flow-ID is unique within the administrative domain and MUST NOT have a value in the reserved label space (0-15) [RFC3032].¶

5. 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 the 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, whereas [I-D.xzc-lsr-mpls-flc-frld] provides a method to achieve that.¶

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. In order to overcome this potential challenge, an implementation MAY provide flexibility to the ingress node to place FL between SID labels, i.e., multiple identical FLs at different depths MAY be interleaved with SID labels, when that happens a sophisticated network planning may be needed and it's beyond the scope of this document.¶

6. 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 SFL, and the two solutions proposed for SFL would also apply here.¶

7. Security Considerations

This document introduces the performance measurement domain that is the scope of a Flow-ID label. The Flow-ID Label Indicator and Flow-ID label MUST NOT be signaled and distributed outside one performance measurement domain. Improper configuration so that the Flow-ID label being passed from one domain to another would likely result in potential Flow-ID conflicts.¶

To prevent packets carrying Flow-ID label from leaking from one domain to another, the domain boundary nodes SHOULD deploy some policies (e.g., ACL) to filter out the packets. Specifically, in the sending edge, the domain boundary node SHOULD filter out the packets that carry the Flow-ID Label Indicator and are sent to other domain; in the receiving edge, the domain boundary node SHOULD drop the packets that carry the Flow-ID Label Indicator and are from other domains.¶

8. IANA Considerations

In the Special-Purpose MPLS Label Values registry, a new Extended Special-Purpose MPLS Label Value for the Flow-ID Label Indicator is requested from IANA as follows:¶

9. 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, and Ximing Dong for their careful review and very helpful comments.¶

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

10. Contributors

Minxue Wang
China Mobile
Email: [email protected]¶

Wen Ye
China Mobile
Email: [email protected]¶

11. References