MPLS Data Plane Encapsulation for In-situ OAM Data

MPLS Data Plane Encapsulation for In-situ OAM Data Cisco Systems, Inc.

Canada rgandhi@cisco.com

Cisco Systems, Inc.

zali@cisco.com

Cisco Systems, Inc.

Hansaallee 249, 3rd Floor DUESSELDORF, NORDRHEIN-WESTFALEN 40549 Germany fbrockne@cisco.com

Comcast

Bin_Wen@cable.comcast.com

Orange

bruno.decraene@orange.com

Futurewei Technologies

USA haoyu.song@futurewei.com

Comcast

Voitek_Kozak@comcast.com

MPLS Working Group In-situ Operations, Administration, and Maintenance (IOAM) is used for recording and collecting operational and telemetry information while the packet traverses a path between two points in the network. This document defines how IOAM data fields are transported with MPLS data plane encapsulation using MPLS Network Action (MNA) and follows the MNA framework defined in draft-ietf-mpls-mna-fwk.

Introduction In-situ Operations, Administration, and Maintenance (IOAM) is used for recording and collecting operational and telemetry information while the packet traverses a path between two points in the network. 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. The IOAM data fields are defined in . The IOAM data fields are further updated in for direct export use-cases. This document defines how IOAM data fields are transported with MPLS data plane encapsulations using MPLS Network Action (MNA) and follows the framework defined in . defines mechanisms for carrying MNA header and Network Actions Sub-stack (NASS) above the Bottom of the label stack (BOS) and defines mechanisms for carrying Post-Stack Data (PSD) in MPLS extension headers (EHs) after the Bottom of the label stack. This document uses these two mechanisms and describes the procedures for carrying IOAM data fields in an MPLS header. Note: This document uses MNA encoding solutions defined in Individual Internet Drafts as examples. The MNA encoding will be updated to align with the MNA solutions in the WG adopted Internet Drafts when they are available.

Conventions

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 when, and only when, they appear in all capitals, as shown here.

Abbreviations The MPLS Network Action (MNA) terminology defined in are used in this document. Abbreviations used in this document:

PNI: Post-Stack Network Action Presence Indicator (P flag)
ECMP: Equal Cost Multi-Path
E2E: Edge-To-Edge
HBH: Hop-By-Hop
IHS: Ingress-to-Egress, Hop-By-Hop or Select Scope
IOAM: In-situ Operations, Administration, and Maintenance
MPLS: Multiprotocol Label Switching
MNA: MPLS Network Action
OAM: Operations, Administration, and Maintenance
POT: Proof-of-Transit

MPLS Extensions for IOAM Data Fields

IOAM Extension Header The IOAM extension headers containing different IOAM-Data-Fields are added in the MPLS packet as shown in Figure 1. The IOAM-Data-Fields MUST follow the definitions corresponding to the IOAM-Option-Types (e.g., see Section 4.4 of and Section 3 of ). An IOAM extension header uses Extension Header (EH) defined in .

Extension Headers with IOAM Data Fields The 4-Octet Common Header CH) is added with the following fields in the MPLS header as defined in :

1ST-NIBBLE (R):: The first 4-bit is Reserved (value TBA4).
EH-CN (EHC):: The EH Count, number of EHs carried in the packet.
EH-TOTAL-LEN (EHTL):: Total Length of EHs in the packet in 4-octet units.
ORIG-UL-PROTOCOL (OUL):: The Original Upper Layer Protocol.
NEXT-HDR (NH):: The Next Header protocol. For IOAM as Next Header, value TBA2 is to be assigned by IANA.

IOAM-Data-Fields are added in EHs containing the following fields:

IOAM-OPT-TYPE:: 8-bit field defining the IOAM Option type, as defined in the "IOAM Option-Type Registry" specified in and ).
IOAM-HDR-LEN:: 8-bit unsigned integer. Length of the IOAM Header in 4-octet units.
IOAM Option and Data Space:: IOAM-Data-Fields as specified by the IOAM-OPT-Type field. IOAM-Data-Fields are defined corresponding to the IOAM-Option-Type (e.g., see Section 4.4 of and Section 3 of .
BLOCK-NUMBER:: The Block Number can be used to aggregate the IOAM data collected in data plane, e.g., to compute measurement metrics for each block of a data flow. It is also used to correlate the IOAM data on different nodes.

MNA Header for Post-Stack Network Action Presence Indicator and Scope The P flag for PNI (Post-Stack Network Action Presence Indicator) defined in is used in this document to indicate the presence of IOAM Post-Stack Network Action and Ancillary Data. A Post-Stack Network Action Presence Indicator (P flag) MUST be set to "1" to indicate the presence of IOAM-Data-Fields in the MPLS header. The IHS scope field defined in is used to indicate that E2E or HBH or Select processing is required for the Post-Stack Network Action and Ancillary Data. If both edge and intermediate nodes need to process the IOAM data fields then IHS scope MUST be set to "HBH, value 0x1". If only edge nodes need to process the IOAM data fields then IHS scope MUST be set to "I2E, value 0x0". The HBH scope allows to optimize the IOAM data processing on the intermediate nodes and avoids the need to parse all IOAM-Data-Fields to detect HBH option types. The MNA Label used in this document is a Base Special Purpose Label (bSPL value TBA1 to be assigned by IANA), and is referred to as Network Action Sub-Stack Indicator (NASI) in .

Edge-to-Edge IOAM Network Action

MNA Header for Edge-To-Edge IOAM The Post-Stack Network Action Presence Indicator is set to "1" to indicate the presence of IOAM-Data-Fields and the IHS scope is set to "I2E, value 0x0" to indicate the scope of E2E IOAM-Data-Fields in the MPLS header as shown in Figure 2.

Example MNA Header for E2E IOAM The E2E IOAM-Data-Fields carry the Option-Type(s) that require processing on the encapsulating and decapsulating nodes only. The IOAM Option-Type carried can be IOAM Edge-to-Edge Option-Type (value 3) as well as Direct Export (DEX) Option-Type (value 4, yet to be assigned by IANA) defined in . The E2E IOAM-Data-Fields SHOULD NOT carry any IOAM Option-Type that require IOAM processing on the intermediate nodes as it will not be processed by them since IHS scope is set to "I2E, value 0x0".

Procedure for Edge-to-Edge IOAM Network Action The E2E IOM Network Action procedure is summarized as following:

The encapsulating node inserts the MNA Label (bSPL value TBA1) with the Post-Stack Network Action Presence Indicator (P flag) set to "1" below the label whose FEC is the decapsulating node and one or more IOAM-Data-Fields in the MPLS packet.
The intermediate nodes do not process IOAM-Data-Fields.
The penultimate node MUST NOT remove the MNA Sub-stack from the MPLS header so that the MNA Sub-stack is received at the decapsulating node. This encapsulating node adds required MPLS header so that the received packet on the penultimate node does not have MNA Sub-stack at the top of the Label stack.
The decapsulating node MAY punt a copy of the packet with the receive timestamp to the slow path for IOAM-Data-Fields processing when the node recognizes the P flag is set to "1". The receive timestamp is required by the various E2E OAM use-cases, including streaming telemetry. Note that the packet is not necessarily punted to the control-plane.
The decapsulating node processes the IOAM-Data-Fields using the procedures defined in . An example of IOAM processing is to export the IOAM-Data-Fields, send IOAM-Data-Fields via streaming telemetry, etc.
The decapsulating node MUST remove the IOAM-Data-Fields from the received packet. The decapsulated packet is forwarded downstream or terminated locally similar to the regular IOAM-Data-Fields.

Hop-By-Hop IOAM Network Action

MNA Header for Hop-By-Hop IOAM The Post-Stack Network Action Presence Indicator is set to "1" to indicate the presence of IOAM-Data-Fields and the IHS scope is set to "HBH, value 0x1" to indicate the scope of HBH IOAM-Data-Fields in the MPLS header as shown in Figure 3.

Example MNA Header for HBH IOAM The HBH IOAM-Data-Fields carry the Option-Type(s) that require processing at the intermediate and/or encapsulating and decapsulating nodes. The IOAM Option-Type carried can be IOAM Pre-allocated Trace Option-Type (value 0), IOAM Incremental Trace Option-Type (value 1) and IOAM Proof of Transit (POT) Option-Type (value 2), and Edge-to-Edge Option-Type (value 3) defined in as well as Direct Export (DEX) Option-Type (value 4, yet to be assigned by IANA) defined in .

Procedure for Hop-By-Hop IOAM Network Action The Hop-By-Hop IOAM Network Action procedure is summarized as following:

The encapsulating node inserts the MNA Label (bSPL value TBA1) with the Post-Stack Network Action Presence Indicator (P flag) and IHS scope set to "HBH, value 0x1" below the label whose FEC is the decapsulating node and one or more IOAM-Data-Fields in the MPLS packet.
The intermediate node enabled with HBH IOAM function processes the data packet including the IOAM-Data-Fields as defined in and when the node recognizes the HBH Processing Indicator in the MPLS header.
The intermediate node MAY punt a copy of the packet with the receive timestamp to the slow path for IOAM-Data-Fields processing when the node recognizes the HBH Processing Indicator. The receive timestamp is required by the various HBH OAM use-cases, including streaming telemetry. Note that the packet is not necessarily punted to the control-plane.
The intermediate node forwards a copy of the processed data packet downstream.
The behavior on the penultimate node is same as E2E case.
The processing on the decapsulating node is same as E2E case.

Hop-By-Hop and Edge-To-Edge IOAM Extension Headers Both HBH and E2E IOAM EHs may be added in an MPLS header. In this case the HBH IOAM EHs MUST be added after the BOS and before the E2E IOAM EHs. When an intermediate node that processes the HBH IOAM EHs, encounters the first E2E IOAM EH, it will stop processing of the E2E EH.

Procedure for Select IOAM Network Action The procedure for carrying the IOAM for Select is the same as HBH IOAM except the IHS scope is set to "Select, value 0x2". In this case, only the select nodes will process the IOAM-Data-Fields.

Considerations for IOAM

Considerations for ECMP The encapsulating node needs to make sure the IOAM-Data-Fields do not start with a well-known IP Version Number (e.g. 0x4 for IPv4 and 0x6 for IPv6) as that can alter the hashing function for ECMP that uses the IP header. This is achieved by using the Common Header (CH) with a different IP Version Number (value TBA4) after the MPLS label stack.

Node Capability The decapsulating node that has to remove the IOAM-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. The node that does not recognize the MNA Label received at the top of the label stack will drop the packet.

Nested MPLS Encapsulation When a packet is received with MPLS Encapsulated IOAM Network Action, the nested MPLS encapsulating node that supports a different IOAM Network Action, the node MUST add a new MNA Label (with Sub-Stack) with the supported IOAM Network Action as part of the new MPLS encapsulation.

Security Considerations The security considerations of IOAM in general are discussed in and apply to the procedure defined in this document. IOAM is considered a "per domain" feature, where one or several operators decide on configuring IOAM according to their needs. IOAM is intended for deployment in limited domains . As such, it assumes that a node involved in IOAM operation has previously verified the integrity of the path. Still, operators need to properly secure the IOAM domain to avoid malicious configuration and use, which could include injecting malicious IOAM packets into the domain.

IANA Considerations The encoding of Next-Header uses the same value registry for IPv4/ IPv6 protocol numbers. The value TBA2 for IOAM as Next Header shall be assigned by IANA from the "Protocol Numbers" registry (https://www.iana.org/assignments/protocol-numbers/protocol-numbers.xhtml).

References Normative References Key words for use in RFCs to Indicate Requirement Levels Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. In-situ OAM Direct Exporting Futurewei Nvidia Cisco Thoughtspot Huawei Data Fields for In Situ Operations, Administration, and Maintenance Cisco Systems, Inc. Thoughtspot Huawei MPLS Network Action Header Encodings Cisco Systems, Inc. Cisco Systems, Inc. Broadcom Futurewei Technologies Juniper Networks MPLS Extension Header Futurewei Technologies Huawei Huawei Bronze Dragon Consulting Juniper Networks Cisco Systems Cisco Systems Cisco Systems Informative References MPLS Network Actions Framework Limited Domains and Internet Protocols

Acknowledgements The authors would like to thank Patrick Khordoc, Sagar Soni, Shwetha Bhandari, Clarence Filsfils, and Vengada Prasad Govindan for the discussions on IOAM. The authors would also like to thank Tarek Saad, Loa Andersson, Greg Mirsky, Stewart Bryant, Xiao Min, and Cheng Li for providing many useful comments. The authors would also like to thank Mach Chen, Andrew Malis, Matthew Bocci, and Nick Delregno for the MPLS-RT reviews.