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 live traffic.¶

1. Introduction

[RFC8321] describes a passive 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, the method is often referred to as Alternate Marking Method. [RFC8372] discusses the desired capabilities for MPLS flow identification, in order to perform a better in-band performance monitoring of user data packets.¶

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

This document employs a method, other than Synonymous Flow Label (SFL), to accomplish 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 performance measurement, and the latter mainly aims at end-to-end performance measurement. Different sets of flows may use different methods.¶

The method described in this document is also complementary to the In-situ OAM method [I-D.ietf-ippm-ioam-data] [I-D.ietf-ippm-ioam-direct-export], the former doesn't introduce any new header whereas the latter introduces a new In-situ OAM header, furthermore, the former requests the network nodes to report the data used for performance measurement, and the latter requests the network nodes to report the data used for operational and telemetry information collection. One set of flows may use 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             |  TC |S|      TTL      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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]. Flow-ID Label Indicator is defined in this document as value TBA1.¶

Analogous to Entropy Label Indicator [RFC6790], the TC and TTL for the Extension Label and the Flow-ID Label Indicator SHOULD follow the same field values of that label immediately preceding the Extension Label, otherwise, the TC and TTL for the Extension Label and the Flow-ID Label Indicator MAY be different values if it is known that the Extension Label will not be exposed as the top label at any point along the LSP. The S bit for the Extension Label and the Flow-ID Label Indicator MUST be zero.¶

Flow-ID label is used as MPLS flow identification [RFC8372], its value should be unique within the administrative domain. Flow-ID values can be allocated by an external NMS or a 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.¶

Analogous to Entropy Label [RFC6790], the Flow-ID label can be placed at either the bottom or the middle of the MPLS label stack, and the Flow-ID label MAY appear multiple times in a label stack. Section 2.1 of this document provides several examples to illustrate how to apply Flow-ID label in a label stack. Again analogous to Entropy Label, the TTL for the Flow-ID label MUST be zero to ensure that it is not used inadvertently for forwarding, the TC for the Flow-ID label may be any value, the S bit for the Flow-ID Label depends on whether or not there are more labels in the label stack.¶

Besides flow identification, a color-marking field is also necessary for alternate marking method. To achieve the purpose of coloring the MPLS traffic, the current practice when writing this document is to reuse the Flow-ID label's TC, i.e., using TC's highest order two bits (called double-marking methodology [RFC8321]) as color-marking bits. Alternatively, allocating multiple Flow-ID labels to the same flow may be used for the purpose of alternate marking.¶

+----------------------+
|          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 Extension Label, the Flow-ID Label Indicator, alongside with the Flow-ID label, into the MPLS label stack. At the same time, the ingress node sets the color-marking field, as needed by alternate-marking technique, and sets the Flow-ID value, as defined in this document.¶
• The transit nodes lookup the Flow-ID label with the help of the Extension Label and the Flow-ID Label Indicator, and transmit the collected information to an external NMS or a controller, which includes the values of the block counters and the timestamps of the marked packets, along with the value of the Flow-ID, referring to the procedures of alternate marking method. Note that in order to lookup the Flow-ID label, the transit nodes need to perform some deep packet inspection beyond the label at the top of the label stack used to take forwarding decisions.¶
• The egress node pops the Extension Label and the Flow-ID Label Indicator, alongside with the Flow-ID label, from the MPLS label stack. This document doesn't introduce any new procedure regarding to the process of 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 or the 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 or the controller by IPFIX [RFC7011], then the NMS or the controller would generate one or two Flow-IDs based on the export 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 or the 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 nodes need to lookup both of the two Flow-IDs by default, and that can be changed to e.g. lookup only the Flow-ID applied to MPLS transport by configuration.¶

Whether using manual trigger or using automatic trigger, the NMS or the controller MUST guarantee every generated Flow-ID is unique within the administrative domain.¶

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 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 Flow-ID label at an appropriate depth, which ensures the node that needs to process the Flow-ID label has the FLC. The ingress node SHOULD insert each Flow-ID label within an appropriate FRLD, which is the minimum FRLD of all on-path nodes that needs to read and use the Flow-ID label in question. How the ingress node knows the Flow-ID label processing node has the FLC and the appropriate FRLD for each Flow-ID label are outside the scope of this document, whereas [I-D.xzc-lsr-mpls-flc-flrd] provides a method to achieve that.¶

When SR paths are used as 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 Flow-ID label 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 Flow-ID label between SID labels, i.e., multiple identical Flow-ID labels 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 a Flow-ID label may cause the same problem as the introduction of an SFL, and the two solutions proposed for the problem caused by the introduction of 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 end, 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 end, 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 defined in [SPL], a new Extended Special-Purpose MPLS Label Value for 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 and Ming Ke 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. References