Internet-Draft | In-situ OAM for MPLS Data plane | January 2022 |
Gandhi, et al. | Expires 31 July 2022 | [Page] |
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 with MPLS data plane encapsulation using new Generic Associated Channel (G-ACh) and updates the RFC 5586.¶
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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. The IOAM data fields are defined in [I-D.ietf-ippm-ioam-data], and can be used for various use-cases for OAM. 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 with MPLS data plane encapsulations using 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.¶
Abbreviations used in this document:¶
IOAM Indicator¶
Equal Cost Multi-Path¶
Edge-To-Edge¶
Entropy Label¶
Entropy Label Indicator¶
Entropy Label Control¶
Generic Associated Channel¶
Hop-By-Hop¶
Hop-By-Hop Indicator¶
In-situ Operations, Administration, and Maintenance¶
Multiprotocol Label Switching¶
Operations, Administration, and Maintenance¶
Proof-of-Transit¶
PseudoWire¶
The IOAM data fields are defined in [I-D.ietf-ippm-ioam-data]. The IOAM data fields are carried in the MPLS header as shown in Figure 1. 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.¶
The IOAM data fields are encapsulated using the following fields in the MPLS header:¶
An IOAM Indicator MUST be used 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 IOAM Indicator and HBH Indicator MUST be used. The HBH Indicator allows to optimize the IOAM processing on intermediate nodes by checking if IOAM data fields need to be processed.¶
[RFC6790] defines the MPLS Entropy Label (EL) and Entropy Label Indicator (ELI). [I-D.decraene-mpls-slid-encoded-entropy-label-id] defines Entropy Label Control (ELC) field and is carried in the TTL field of the Entropy Label. Additional flags are defined in [I-D.jags-mpls-ext-hdr-entropy-lbl]. A flag called IOI (IOAM Indicator) in the ELC is defined in this document to indicate the presence of IOAM. A flag called HBI (Hop-By-Hop Indicator) in the ELC is defined in [I-D.jags-mpls-ext-hdr-entropy-lbl] to indicate that HBH processing is required. The bit positions of these flags in the ELC field can be user-defined, consistently in the network. Alternatively, the bit positions of these flag can be allocated by IANA.¶
The IOAM Indicator (Flag IOI in the Entropy Label Control field) is used to indicate the presence of the IOAM data fields in the MPLS header as shown in Figure 2.¶
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 [I-D.ietf-ippm-ioam-data]. 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 IOAM Indicator (Flag IOI) along with Hop-By-Hop Indicator (Flag HBI) in the Entropy Label Control field) are used to indicate the presence of the HBH IOAM data fields in the MPLS header as shown in Figure 3.¶
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 [I-D.ietf-ippm-ioam-data].¶
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].¶
When entropy label [RFC6790] is used for hashing function for ECMP, the procedure defined in this document does not alter the ECMP behaviour.¶
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 packets with IOAM data fields may carry one or more Entropy Labels with IOAM Indicator in the MPLS header. An intermediate node SHOULD check the first Entropy Label in the label stack for the IOAM Indicator to process the IOAM data fields.¶
An intermediate node that supports IOAM, SHOULD copy the ELC field from the received Entropy Label to the new Entropy Label when inserting the new Entropy Label in the MPLS header and this can be based on a local policy.¶
When a packet is received with an IOAM Indicator, the nested MPLS encapsulating node that supports a different IOAM, the node MUST add a new Entropy Label with the supported IOAM Indicator.¶
The security considerations of IOAM in general are discussed in [I-D.ietf-ippm-ioam-data] 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 is located through the use of the "Length" field in the G-ACh.¶
In this example, BOS (Bottom of Stack) Extension Header defined in [I-D.jags-mpls-ext-hdr-entropy-lbl] is used with BOS Opcode for IOAM (value to be assigned by IANA) (instead of using the G-ACh channel for IOAM defined in this document).¶
Flags NH and H as defined in [I-D.jags-mpls-ext-hdr-entropy-lbl] are used. Bottom of Stack Presence Indicator (BPI) flag in ELC as defined in [I-D.jags-mpls-ext-hdr-entropy-lbl] is set to "1" to indicate the presence of the BOS extension header (instead of using the IOI flag in the ELC defined in this document). There is no change in the usage of the HBI flag.¶
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.¶