MPLS Data Plane Encapsulation for In-situ OAM Data
draft-gandhi-mpls-ioam-sr-02

Abstract

In-situ Operations, Administration, and Maintenance (IOAM) records operational and telemetry information in the data packet while the packet traverses a path between two nodes in the network. This document defines how IOAM data fields are transported using the MPLS data plane encapsulation, including Segment Routing (SR) with MPLS data plane (SR-MPLS).

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Table of Contents

• 1. Introduction
• 2. Conventions
• 2.1. Requirement Language
• 2.2. Abbreviations
• 3. IOAM Data Field Encapsulation in MPLS Header
• 3.1. Indicator Labels
• 4. Procedure for Edge-to-Edge IOAM
• 4.1. Edge-to-Edge IOAM Indicator Label Allocation
• 5. Procedure for Hop-by-Hop IOAM
• 5.1. Hop-by-Hop IOAM Indicator Label Allocation
• 6. Considerations for ECMP
• 7. Node Capability
• 8. Data Packets with SR-MPLS Header
• 9. Security Considerations
• 10. IANA Considerations
• 11. References
• 11.1. Normative References
• 11.2. Informative References
• Acknowledgements
• Contributors
• Authors' Addresses

1. Introduction

In-situ Operations, Administration, and Maintenance (IOAM) records operational and telemetry information within the packet while the packet traverses a particular network domain. The term "in-situ" refers to the fact that the IOAM data fields are added to the data packets rather than being sent within the probe packets specifically dedicated to OAM or Performance Measurement (PM). The IOAM data fields are defined in [I-D.ietf-ippm-ioam-data], and can be used for various use-cases for OAM and PM. The IOAM data fields are further updated in [I-D.ietf-ippm-ioam-direct-export] for direct export use-cases and in [I-D.ietf-ippm-ioam-flags] for Loopback and Active flags.

This document defines how IOAM data fields are transported using the MPLS data plane encapsulations, including Segment Routing (SR) with MPLS data plane (SR-MPLS).

2. Conventions

2.1. Requirement Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

2.2. Abbreviations

Abbreviations used in this document:

ECMP

Equal Cost Multi-Path

IOAM

In-situ Operations, Administration, and Maintenance

MPLS

Multiprotocol Label Switching

OAM

Operations, Administration, and Maintenance

PM

Performance Measurement

POT

Proof-of-Transit

PSID

Path Segment Identifier

SR

Segment Routing

SR-MPLS

Segment Routing with MPLS Data plane

3. IOAM Data Field Encapsulation in MPLS Header

The IOAM data fields defined in [I-D.ietf-ippm-ioam-data] are used. IOAM data fields are carried in the MPLS header as shown in Figure 1 and Figure 2. More than one trace options can be present in the IOAM data fields. The Indicator Label is added at the bottom of the MPLS label stack (S flag set to 1) to indicate the presence of the IOAM data field(s) in the MPLS header.

The data packets with IOAM data fields carry only one Indicator Label in the MPLS header. Any intermediate node that adds additional MPLS encapsulation in the MPLS header may further update the IOAM data fields in the header without inserting another Indicator Label.

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  IOAM Indicator Label                 | TC  |1|  TTL          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+
|  IOAM-Type    | IOAM HDR LEN  |    RESERVED                   |  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  I
|                                                               |  O
|                                                               |  A
~                 IOAM Option and Data Space                    ~  M
|                                                               |  |
|                                                               |  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+
|                                                               |
|                                                               |
|                 Payload + Padding                             |
|                                                               |
|                                                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: IOAM Encapsulation in MPLS Header

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  IOAM and Flow Indicator Label        | TC  |1|  TTL          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0|      Flow label                       | Block Number  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+
|  IOAM-Type    | IOAM HDR LEN  |    RESERVED                   |  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  I
|                                                               |  O
|                                                               |  A
~                 IOAM Option and Data Space                    ~  M
|                                                               |  |
|                                                               |  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+
|                                                               |
|                                                               |
|                 Payload + Padding                             |
|                                                               |
|                                                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: IOAM Encapsulation with Flow Label in MPLS Header

IOAM Indicator Label (IIL) and IOAM and Flow Indicator Label (IFIL) used are defined in this document.

The fields related to the encapsulation of IOAM data fields in the MPLS header are defined as follows:

IOAM-Type:

8-bit field defining the IOAM Option type, as defined in Section 7.2 of [I-D.ietf-ippm-ioam-data].

IOAM HDR LEN:

8-bit unsigned integer. Length of the IOAM HDR in
4-octet units.

RESERVED:

8-bit reserved field MUST be set to zero upon transmission and ignored upon receipt.

IOAM Option and Data Space:

IOAM option header and data is present as defined by the IOAM-Type field, and is defined in Section 4 of [I-D.ietf-ippm-ioam-data].

3.1. Indicator Labels

IOAM Indicator Label (value TBA1 or TBA3) and IOAM and Flow Indicator Label (value TBA2 or TBA4) are used to indicate the presence of the IOAM data field in the MPLS header.

The IOAM and Flow Indicator Label (value TBA2 or TBA4) is used to carry a second label underneath with protocol value 0000b, 20-bit Flow Label and 8-bit Block Number.

• The protocol value 0000b allows to avoid incorrect IP header-based hashing over ECMP paths that uses the value 0x4 (for IPv4) and value 0x6 (for IPv6) [RFC4928].
• The Flow Label identifies the traffic flow that can be used for IOAM purpose, e.g. monitoring a specific traffic flow for latency.
• The Block Number can be used to aggregate the IOAM data collected in data plane, e.g. compute measurement metrics for each block of a flow.

4. Procedure for Edge-to-Edge IOAM

The Edge-to-Edge (E2E) IOAM includes IOAM Option-Type as Edge-to-Edge Option-Type [I-D.ietf-ippm-ioam-data]. This section summarizes the procedure for data encapsulation and decapsulation for Edge-to-Edge IOAM in MPLS header.

• The encapsulating node inserts the IOAM Indicator Label or IOAM Flow Indicator Label with Flow Label and one or more IOAM data field(s) in the MPLS header. The procedure to generate the Flow Label is outside the scope of this document.
• The decapsulating node "forwards and punts the timestamped copy" of the data packet including IOAM data fields when the node recognizes the IOAM Indicator Label and IOAM Flow Indicator Label. The copy of the data packet is punted to the slow path for OAM processing and is not necessarily punted to the control-plane. The receive timestamp is required by various E2E OAM use-cases.
• The decapsulating node processes the IOAM data field(s) using the procedures defined in [I-D.ietf-ippm-ioam-data]. An example of IOAM processing may be to export the data fields, send data fields via Telemetry, etc.
• The decapsulating node also pops the Indicator Label and the IOAM data fields from the MPLS header.

4.1. Edge-to-Edge IOAM Indicator Label Allocation

IOAM Indicator Label (value TBA1) and IOAM and Flow Indicator Label (value TBA2) are used to indicate the presence of the E2E IOAM data field in the MPLS header. The E2E IOAM Indicator Label and IOAM and Flow Indicator Label can be allocated using one of the following methods:

• Labels assigned by IANA with value TBA1 and TBA2 from the Extended Special-Purpose MPLS Values [I-D.ietf-mpls-spl-terminology].
• Labels allocated by a Controller from the global table of the decapsulating node. The Controller provisions the label on both encapsulating and decapsulating nodes.
• Labels allocated by the decapsulating node. The signaling extension for this is outside the scope of this document.

5. Procedure for Hop-by-Hop IOAM

The Hop-by-Hop (HbH) IOAM includes IOAM Option-Types IOAM Pre-allocated Trace Option-Type, IOAM Incremental Trace Option-Type and IOAM Proof of Transit (POT) Option-Type [I-D.ietf-ippm-ioam-data]. This section summarizes the procedure for data encapsulation and decapsulation for Hop-by-hop IOAM in MPLS header.

• The encapsulating node inserts the IOAM Indicator Label or IOAM Flow Indicator Label with Flow Label and one or more IOAM data field(s) in the MPLS header. The procedure to generate the Flow Label is outside the scope of this document.
• The intermediate and decapsulating node enabled with IOAM functions "forwards and punts the timestamped copy" of the data packet including IOAM data fields when the node recognizes the IOAM Indicator Label and IOAM Flow Indicator Label. The copy of the data packet is punted to the slow path for OAM processing and is not necessarily punted to the control-plane. The receive timestamp is required by various hop-by-hop OAM use-cases.
• The intermediate and decapsulating node processes the IOAM data field(s) using the procedures defined in [I-D.ietf-ippm-ioam-data]. An example of IOAM processing may be to export the data fields, send data fields via Telemetry, etc.
• The decapsulating node pops the Indicator Label and the IOAM data fields from the MPLS header.

5.1. Hop-by-Hop IOAM Indicator Label Allocation

IOAM Indicator Label (value TBA3) and IOAM and Flow Indicator Label (value TBA4) are used to indicate the presence of the HbH IOAM data field in the MPLS header. The HbH IOAM Indicator Label and IOAM and Flow Indicator Label can be allocated using one of the following methods:

• Labels assigned by IANA with value TBA3 and TBA4 from the Extended Special-Purpose MPLS Values [I-D.ietf-mpls-spl-terminology].
• Labels allocated by a Controller from the network-wide global table. The Controller provisions the labels on all nodes participating in IOAM functions along the data traffic path.

6. Considerations for ECMP

The encapsulating node needs to make sure the IOAM data field does not start with a well known IP protocol value (e.g. 0x4 for IPv4 and 0x6 for IPv6) as it can alter the hashing function for ECMP that uses the IP header. This can be achieved by using the IOAM and Flow Indicator Label (value TBA2 and TBA4) that follows by protocol value 0000b. This approach is consistent with utilizing 0000b as the first nibble after the MPLS label stack, as described in [RFC4928] [RFC4385].

Note that the hashing function for ECMP that uses the labels from the MPLS header may now include the Indicator Label.

When entropy label [RFC6790] is used for hashing function for ECMP, the procedure defined in this document does not alter the hashing function.

7. Node Capability

The decapsulating node that has to pop the Indicator Label, data fields, and perform the IOAM function may not be capable of supporting it. The encapsulating node needs to know if the decapsulating node can support the IOAM function. The signaling extension for this capability exchange is outside the scope of this document.

The intermediate node that is not capable of supporting the IOAM functions defined in this document, can simply skip the IOAM processing of the MPLS header.

8. Data Packets with SR-MPLS Header

Segment Routing (SR) technology leverages the source routing paradigm [RFC8660]. A node steers a packet through a controlled set of instructions, called segments, by pre-pending the packet with an SR header. In the SR with MPLS data plane (SR-MPLS), the SR header is instantiated through a label stack.

An example of data packet carrying the SR-MPLS header with Path Segment Identifier (PSID) [I-D.ietf-spring-mpls-path-segment] with IOAM encapsulation is shown in Figure 3. The Path Segment Identifier allows to identify the path associated with the data traffic being monitored for IOAM on the decapsulating node.

  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                Label(1)               | TC  |S|      TTL      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 .                                                               .
 .                                                               .
 .                                                               .
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                Label(n)               | TC  |S|      TTL      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                PSID                   | TC  |S|      TTL      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                Packet as shown in Figure 1 or Figure 2        |
 .                                                               .
 +---------------------------------------------------------------+

Figure 3: Data Packet with SR-MPLS Header

9. Security Considerations

The security considerations of SR-MPLS are discussed in [RFC8660], and the security considerations of IOAM in general are discussed in [I-D.ietf-ippm-ioam-data].

IOAM is considered a "per domain" feature, where one or several operators decide on leveraging and configuring IOAM according to their needs. Still, operators need to properly secure the IOAM domain to avoid malicious configuration and use, which could include injecting malicious IOAM packets into a domain.

10. IANA Considerations

IANA maintains the "Special-Purpose Multiprotocol Label Switching (MPLS) Label Values" registry (see <https://www.iana.org/assignments/mpls-label-values/mpls-label-values.xml>). IANA is requested to allocate IOAM Indicator Label value and IOAM and Flow Indicator value from the "Extended Special-Purpose MPLS Label Values" registry:

11. References

11.1. Normative References

11.2. Informative References

Acknowledgements

The authors would like to thank Patrick Khordoc, Shwetha Bhandari and Vengada Prasad Govindan for the discussions on IOAM. The authors would also like to thank Tarek Saad, Loa Andersson and Cheng Li for providing many useful comments.

Contributors

Sagar Soni
Cisco Systems, Inc.

Email: sagsoni@cisco.com

Authors' Addresses