LSP Ping/Traceroute for Enabled In-situ OAM Capabilities

MPLS encapsulation for In-situ OAM (IOAM) data is defined in , which utilizes MPLS Network Actions (MNA) techniques () to carry IOAM data fields (, ) in MPLS packets. As specified in , the echo request/reply can be used by the IOAM encapsulating node to discover the enabled IOAM capabilities at IOAM transit and decapsulating nodes. defines a probe message called "MPLS echo request", and a response message called "MPLS echo reply" for returning the result of the probe. This document describes the MPLS Node IOAM Information Query functionality, which uses the MPLS echo request/reply messages, allowing the IOAM encapsulating node to discover the enabled IOAM capabilities of each IOAM transit and IOAM decapsulating node. specifies "ping" and "traceroute" modes. In "ping" mode, the ingress LSR sends a single MPLS echo request with the TTL in the outermost label stack entry set to 255. The MPLS echo request is intended to reach the end of the path and only the egress LSR is expected to respond with the MPLS echo reply. In "traceroute" mode, the ingress LSR transmits a sequence of MPLS echo requests with the TTL value being set in successive probe packets to 1, 2, and so on. Using TTL expiration as the exception mechanism, each LSR is expected to respond by transmitting an MPLS echo reply. In an MPLS network, the ingress LSR may also act as the IOAM encapsulating node. In such a case, a transit LSR acts as the IOAM transit node, and the egress LSR acts as the IOAM decapsulating node. Usually, the trace option of IOAM data is needed, the IOAM encapsulating node requires to query the enabled IOAM capabilities of each IOAM transit and decapsulating node, then the "traceroute" mode can be used. In case that only the edge to edge option of IOAM data is needed, the IOAM encapsulating node requires to query the enabled IOAM Capabilities of only the IOAM decapsulating node, then the "ping" mode can be used. The mechanism specified in this document applies to both point-to-point (P2P) MPLS LSP and point-to-multipoint (P2MP) MPLS LSP.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

The IOAM Capabilities Query TLV presented in Figure 1 is carried as a TLV of the MPLS Echo Request message:

Type: Indicates the IOAM Capabilities Query TLV. The value is TBA1. Length: The length of the TLV's Value field in octets. The Value field is a List of IOAM Namespace-IDs, which is also called IOAM Capabilities Query Container Payload in Section 3.1 of .

The format of an IOAM Capabilities Query can vary from deployment to deployment. In a deployment where only the default Namespace-ID is used, the IOAM Capabilities Query is depicted as the following:

In a deployment where two Namespace-IDs (Namespace-ID1 and Namespace-ID2) are used, the IOAM Capabilities Query is depicted as the following:

The IOAM Capabilities Response TLV presented in Figure 4 is carried as a TLV of the MPLS Echo Reply message:

Type: Indicates the IOAM Capabilities Response TLV. The value is TBA2. Length: The length of the TLV's Value field in octets. The Value field is a List of IOAM Capabilities Objects, which is also called IOAM Capabilities Response Container Payload in Section 3.2 of . Each IOAM Capabilities Object is encoded in a sub-TLV format.

All IOAM Capabilities sub-TLVs (aka Objects) are encapsulated in an IOAM Capabilities Response TLV of an MPLS Echo Reply message. Each IOAM Capabilities sub-TLV has the following format:

Sub-type: Indicates the IOAM Capabilities sub-TLVs. The values are listed as the following:

Length: The length of the sub-TLV's Value field in octets. The Value field of the IOAM Capabilities sub-TLV is the IOAM Capabilities Object Payload, which is defined in Sections 3.2.1, 3.2.3, 3.2.4, 3.2.5, and 3.2.6 of .

The format of an IOAM Capabilities Response can vary from deployment to deployment. In a deployment where only the default Namespace-ID is used, the IOAM Pre-allocated Tracing Capabilities and IOAM Proof of Transit Capabilities are enabled at an IOAM transit node, if that IOAM transit node received an MPLS echo request containing IOAM Capabilities Query TLV, then the IOAM Capabilities Response TLV contained in an MPLS echo reply is depicted as the following:

In a deployment where two Namespace-IDs (Namespace-ID1 and Namespace-ID2) are used, for both Namespace-ID1 and Namespace-ID2 the IOAM Pre-allocated Tracing Capabilities and IOAM Proof of Transit Capabilities are enabled at an IOAM transit node, if that IOAM transit node received an MPLS echo request containing IOAM Capabilities Query TLV, then the IOAM Capabilities Response TLV contained in an MPLS echo reply is depicted as the following:

Note that multiple sub-TLVs with the same sub-type may be present in an IOAM Capabilities Response TLV, as long as the Namespace-IDs in these sub-TLVs are all different. In a deployment where only the default Namespace-ID is used, the IOAM Pre-allocated Tracing Capabilities, IOAM Proof of Transit Capabilities and IOAM Edge-to-Edge Capabilities are enabled at the IOAM decapsulating node, if that IOAM decapsulating node received an MPLS echo request containing IOAM Capabilities Query TLV, then the IOAM Capabilities Response TLV contained in an MPLS echo reply is depicted as the following:

The Return Code field in the MPLS echo reply MUST be set to (TBA3) No Matched Namespace-ID if any of the following conditions apply: The IOAM Capabilities Query TLV does not include any Namespace-ID. None of the contained list of IOAM Namespace-IDs is recognized. None of the contained list of IOAM Namespace-IDs is enabled.

Section 4 of provides an operational guide on how to use echo request/reply for discovering enabled IOAM capabilities at network nodes, which applies to this document as well. Specifically, if only the IOAM Edge-to-Edge Option-Type is enabled for an MPLS LSP, then LSP Ping in "ping" mode would be operated, which means the LSP ingress node would send a single MPLS echo request to the LSP egress node for discovering its IOAM Edge-to-Edge Capabilities; if other IOAM Option-Type than the Edge-to-Edge Option-Type is enabled for an MPLS LSP, e.g., the IOAM Pre-allocated Trace Option-Type is enabled for an MPLS LSP, then LSP Ping in "traceroute" mode would be operated, which means the LSP ingress node would send a sequence of MPLS echo requests with TTL equal to 1, 2, 3, and so on, until the LSP ingress node receives an MPLS echo reply sent by the LSP egress node. Considering the IOAM function is resource-consuming, in an MPLS network with high number LSPs, usually not all the LSPs are IOAM enabled, in that case, the LSP Ping mechanism for IOAM capabilities discovery would be executed only with the IOAM-enabled LSPs.

This document does request that IANA assigns two new TLVs, and new sub-TLV registry for one of the new TLVs, 5 sub-TLVs to initially populate this registry and a new return code (TBA3).

IANA is requested to assign two new TLVs (TBA1 and TBA2) from the "TLV" registry in the "Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters" registry group. The TLVs' values should be assigned from the range of TLVs that require an error message if the TLV is not recognized. If possible the two lowest free values should be used for these TLVs. Type TLV Name Reference Sub-TLV Registry TBA1IOAM Capabilities QueryThis documentNo Sub-TLVs TBA2IOAM Capabilities ResponseThis document

A new sub-TLV registry should be created for the TLV TBA2 created in Section 6.1. The registration procedures for this sub-TLV registry shall be: Range Registration Procedure Note 0-16383Standards ActionThis range is for TLVs that require an error message if not recognized. (, Section 3.1) 16384-31739RFC RequiredThis range is for TLVs that require an error message if not recognized. (, Section 3.1) 31740-31743Experimental UseReserved, not to be assigned. This range is for TLVs that require an error message if not recognized. (, Section 3.1) 31744-32767First Come First ServedThis range is for TLVs that require an error message if not recognized. (, Section 3.1) 32768-49161Standards ActionThis range is for TLVs that can be silently dropped if not recognized. 49162-64507RFC RequiredThis range is for TLVs that can be silently dropped if not recognized. 64508-64511Experimental UseReserved, not to be assigned. This range is for TLVs that can be silently dropped if not recognized. 64512-65535First Come First ServedThis range is for TLVs that can be silently dropped if not recognized. This sub-TLV registry should initially be populated with the following values. Sub-Type Sub-TLV name Reference Comment 0ReservedThis document 1IOAM Pre-allocated Tracing Capabilities ObjectThis document 2IOAM Proof of Transit Capabilities ObjectThis document 3IOAM Edge-to-Edge Capabilities ObjectThis document 4IOAM DEX Capabilities ObjectThis document 5IOAM End-of-Domain ObjectThis document

IANA is requested to assign a new Return Code from the "Return Code" registry in the "Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters" registry group as follows: Value Meaning Reference TBA3 No Matched Namespace-ID This document

Security issues discussed in and apply to this document. This document recommends that the network operators establish policies that restrict access to MPLS Node IOAM Information Query functionality. In order to enforce these policies, nodes that support MPLS Node IOAM Information Query functionality are RECOMMENDED to support the following configuration options: Enable/disable MPLS Node IOAM Information Query functionality. By default, MPLS Node IOAM Information Query functionality is disabled. Define enabled Namespace-IDs. By default, all Namespace-IDs except the default one (i.e., Namespace-ID 0x0000) are disabled. While applying the MPLS Node IOAM Information Query to P2MP MPLS LSP, since a single MPLS echo request may trigger multiple echo replies, there are scaling concerns and some mitigation measures, e.g., containing the Echo Jitter TLV in the MPLS echo request, as being specified in , MAY be applied.

The authors would like to acknowledge Tarek Saad for his comments on the idea of using LSP Ping for MPLS IOAM Capabilities Discovery. The authors would like to acknowledge Adrian Farrel for his insightful review and comments.