I have reviewed this document as part of the Operational directorate's ongoing effort to review all IETF documents being processed by the IESG.  These comments were written with the intent of improving the operational aspects of the IETF drafts. Comments that are not addressed in last call may be included in AD reviews during the IESG review.  Document editors and WG chairs should treat these comments just like any other last call comments.

This document extends MPLS Ping and Traceroute mechanism from one single domain to multi-domain, multi-AS and provide end to end path tracing and reachability checking across SR MPLS data plane.

This document is on the right track, however I have a few comments to the latest v-14 as follows:
Major issues:
No

Minor issues:
1. Section 3
s/Reply Path (RP) TLv/Reply Path (RP) TLV
2. Section 4.2
s/Length is 8 or 12./Length is 8 without SID included or 12 with SID included.
2. Section 4.2
s/when A-Flag as defined in Section 4.4is present./when A-Flag as defined in Section 4.4 is present.
3. Section 4.3
s/Length is 20 or 24./Length is 20 without SID included or 24 with SID included.
4. Section 5
not sure we need a dedicated section to claim that SRv6 is not in the scoped, can you consolidate the text into introduction section.
5. Section 8 said:
"
 For this purpose, Reply Path TLV in the echo reply
   corresponds to the return path to be used in building the next echo
   request.

      Value         Meaning
      ------        ----------------------
      TBA1        Use Reply Path TLV in the echo reply
                  for building the next echo request.
"
I believe new value should be specified in section 4 while other section can reference the value specified in section 4.

6. Section 8.1 said:
"
 In such cases, ASBR that supports this document MUST set the
   return code TBA2 to indicate local policies do not allow the dynamic
   return path building.

      Value         Meaning
      ------        ---------------------------------------------------
       TBA2        Local policy does not allow dynamic return Path
                   building.
"
Similarly, I think new return code should be specified in section 4, section 8.1 can references the return code specified in section 4.

7. Section 6, 7,8
It lacks clarity for usage examples in section 7 and section 8.2,
can you provide work flow for usage examples in section 7 and section 8.2 to help readers better understand how the mechanism works in this document.
Would it be great to consolidate section 6 and section 8 for protocol operation, e.g. split into two sub sections, one focuses on headend with complet topology visibility while the other focuses on headend with partial topology visibility.

8. Section 6
I know MPLS Ping and Traceroute mechanism is generic mechanism, any network node can be originator and receiver of LSP ping and Traceroute message, but in this inter-domain, inter-AS scenarios, can we make the similar assumption, 
o any network node can be originator and receiver of Eco-Request and Eco-reply? 
o or only ingress node or PE node can be the originator of Eco-request? 
o only egress node or PE node can be receiver of the Eco-request?
o any transit node can be receiver of the Eco-request?
From the current text in section 6, it is not clear about this, can you clarify this?

9. Section 8
what if downstream routers can identify multiple reverse paths for MPLS traceroute? 
Can you make clear who can be downstream routers? Ingress node of each domain or egress node in each domain or any internal node within the domain?