| Internet-Draft | In-situ OAM for MPLS Data plane | July 2022 |
| Gandhi, et al. | Expires 7 January 2023 | [Page] |
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) with new Generic Associated Channel (G-ACh) and updates the RFC 5586.¶
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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 [RFC9197]. The IOAM data fields are further updated in [I-D.ietf-ippm-ioam-direct-export] for direct export use-cases.¶
This document defines how IOAM data fields are transported with MPLS data plane encapsulations using MPLS Network Action (MNA) with new Generic Associated Channel (G-ACh) and updates the [RFC5586].¶
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.¶
The MPLS Network Action (MNA) terminology defined in [I-D.andersson-mpls-mna-fwk] are used in this document.¶
Abbreviations used in this document:¶
Post-Stack Network Action Presence Indicator¶
Equal Cost Multi-Path¶
Edge-To-Edge¶
Generic Associated Channel¶
Hop-By-Hop¶
Hop-By-Hop Post-Stack Network Action Processing Indicator¶
In-situ Operations, Administration, and Maintenance¶
Multiprotocol Label Switching¶
MPLS Network Action¶
Operations, Administration, and Maintenance¶
Proof-of-Transit¶
PseudoWire¶
The IOAM header is added containing different IOAM-Data-Fields in the MPLS header as shown in Figure 1. The IOAM-Data-Fields MUST follow the definitions corresponding to IOAM-Option-Types (e.g. see Section 4.4 of [RFC9197] and Section 3 of [I-D.ietf-ippm-ioam-direct-export]). More than one trace options can be present in the IOAM-Data-Fields.¶
G-ACh [RFC5586] provides a mechanism to transport OAM and other control messages over MPLS data plane. The IOAM G-ACh header [RFC5586] with new IOAM G-ACh type MUST be added immediately after the MPLS label stack in the MPLS header as shown in Figure 1, before the IOAM-Data-Fields. The G-ACh label (GAL) [RFC5586] MUST NOT be added in the MPLS label stack.¶
This document updates the following paragraph in Section 2.1 of [RFC5586]: "The G-ACh MUST NOT be used to transport user traffic" to "The G-ACh MAY be used with user traffic to transport OAM information".¶
Note that the G-ACh is not really used to transport the user traffic in this document but to transport the IOAM-Data-Fields with the user traffic.¶
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+ |0 0 0 1|Version| Length | IOAM G-ACh | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | IOAM-OPT-Type | IOAM HDR Len | Block Number | Reserved | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ I | | O | | A ~ IOAM Option and Data Space ~ M | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+ | | | | | Optional Payload + Padding | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The IOAM-Data-Fields are encapsulated using the following fields in the MPLS header:¶
A Post-Stack Network Action Presence Indicator MUST be added to indicate the presence of the IOAM-Data-Fields in the MPLS header. If both edge and intermediate nodes need to process IOAM data then both Presence Indicator and HBH Network Action Processing Indicator MUST be added. The HBH Processing Indicator allows to optimize the IOAM processing on intermediate nodes and avoids the need to parse all IOAM-Data-Fields.¶
A flag called PNI (Post-Stack Network Action Presence Indicator) in the TTL field defined in [I-D.jags-mpls-mna-hdr] is used in this document to indicate the presence of IOAM Post-Stack Network Action and Ancillary Data. A flag called HPI (Hop-By-Hop Post-Stack Network Action Processing Indicator) in the TTL field defined in [I-D.jags-mpls-mna-hdr] is used to indicate that HBH processing in Post-Stack Network Action and Ancillary Data is required.¶
The MNA Label used in this document is a Special Purpose Label (value TBA2) assigned by IANA, and is defined as Network Action Sub-Stack Indicator (NASI) in [I-D.jags-mpls-mna-hdr].¶
The Post-Stack Network Action Presence Indicator is used to indicate the presence of the IOAM-Data-Fields in the MPLS header as shown in Figure 2.¶
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 | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MNA Label (SPL value TBA2) | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | TC |1| PNI=1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Packet as shown in Figure 1 | . . +---------------------------------------------------------------+
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 [RFC9197]. 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.¶
The E2E IOM procedure is summarized as following:¶
The Post-Stack Network Action Presence Indicator (TTL Flag PNI) along with Hop-By-Hop Processing Indicator (TTL Flag HPI) are used to indicate the presence of the HBH IOAM-Data-Fields in the MPLS header as shown in Figure 3.¶
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 | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MNA Label (SPL value TBA2) | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | TC |1| PNI=1, HPI | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Packet as shown in Figure 1 | . . +---------------------------------------------------------------+
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, IOAM Incremental Trace Option-Type and IOAM Proof of Transit (POT) Option-Type, as well as Edge-to-Edge Option-Type [RFC9197].¶
The HBH IOAM procedure is summarized as following:¶
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 IOAM G-ACh with IP Version Number 0001b after the MPLS label stack [RFC5586].¶
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 intermediate node that does not understand the MNA Label received at the top of the label stack will drop the packet.¶
When a packet is received with IOAM, the nested MPLS encapsulating node that supports a different IOAM, the node MUST add a new MNA Label with the supported IOAM as part of the new MPLS encapsulation.¶
The security considerations of IOAM in general are discussed in [RFC9197] 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 [RFC8799]. 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.¶
Routers that support G-ACh are subject to the same security considerations as defined in [RFC4385] and [RFC5586].¶
IANA maintains G-ACh Type Registry (see https://www.iana.org/assignments/g-ach-parameters/g-ach-parameters.xhtml). IANA is requested to allocate a value for IOAM G-ACh Type from "MPLS Generalized Associated Channel (G-ACh) Types (including Pseudowire Associated Channel Types)" registry.¶
| Value | Description | Reference |
|---|---|---|
| TBA1 | IOAM G-ACh Type | This document |
The IOAM-Data-Fields, including IOAM G-ACh header are added in the MPLS encapsulation immediately after the MPLS header. Any Control Word [RFC4385] or another G-ACh [RFC5586] MUST be added after the IOAM-Data-Fields in the packet as shown in the Figure 4 and Figure 5, respectively. This allows the intermediate nodes to easily access the HBH IOAM-Data-Fields located immediately after the MPLS header. The decapsulating node can remove the MPLS encapsulation including the IOAM-Data-Fields and then process the Control Word or another G-ACh following it. The subsequent G-ACh and Control Word are located through the use of the "Length" field in the IOAM G-ACh.¶
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MNA Label (SPL value TBA2) | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | TC |1| PNI=1, HPI | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0 0 0 1|Version| Length | IOAM G-ACh | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+ | IOAM-OPT-Type | IOAM HDR Len | Block Number | Reserved | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ I | | O | | A ~ IOAM Option and Data Space ~ M | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+ |0 0 0 0| Specified by PW Encapsulation [RFC4385] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | ~ Payload + Padding ~ | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MNA Label (SPL value TBA2) | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | TC |1| PNI=1, HPI | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0 0 0 1|Version| Length | IOAM G-ACh | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+ | IOAM-OPT-Type | IOAM HDR Len | Block Number | Reserved | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ I | | O | | A ~ IOAM Option and Data Space ~ M | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+ |0 0 0 1|Version| Reserved | Channel Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | ~ Payload + Padding ~ | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.¶