Re: [mpls] QA Review draft-akiya-mpls-lsp-ping-reply-mode-simple-03

Hi Nobo and Lou,

To chime in regarding the Reply Path TLV, please see inline...

Snipped.

> > - Section 4.1.1
> >  o The Reply Path TLV carrying {FEC X, FEC Y} Wouldn't it be cleaner,
> > particularly when considering non-draft supporting implementations, to
> > use multiple Reply Path TLVs (one per possible reply path)?
> 
> [NOBO] I believe authors of RFC7110 (which defines the Reply Path TLV) can
> clarify its usage, but here's the way I understand that document.
> 
> - Number of Reply Path TLVs that can appear in the MPLS Echo Request/Reply
> messages is not strictly enforced in the document.
> - The document defines and describes scenarios where one Reply Path TLV is in
> the MPLS Echo Request/Reply (that can carry multiple return FECs).
> - The document does not spell out what happens when there are more than one
> Reply Path TLVs in the MPLS Echo Request/Reply messages (i.e. which takes
> precedence).
> 
> Hence I assumed that author intended that MPLS Echo Request/Reply can carry
> only one Reply Path TLV. And hence, I descried the 4.1.1 example as one Reply
> Path TLV carrying {FEC X, FEC Y} instead of having multiple Reply Path TLVs. After
> scanning through RFC7110, I still think my understanding of the document is
> probably what the author intended.

Yes, your understanding is align with the original intention of RFC7110, there is an implicit assumption that there will be only one Reply TLV that can appear in the MPLS Echo Request/Reply. But the assumption was based on that there will be only one return path specified or chosen. 

For multiple return paths case, IMHO, either single Reply Path TLV with multiple sub-TLVs or multiple Reply Path TLVs is technically workable.

Best regards,
Mach

> 
> I suppose the last two comments are sort of related. Do let me know your
> thoughts after reading my repose to you.
> 
> >
> > That's it,
> > Lou
> 
> Again, many thanks for thorough review!
> 
> Thanks!
> 
> -Nobo
> 
> 
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