Re: [mpls] MPLS-RT review on draft-ninan-mpls-spring-inter-domain-oam-02

[Shraddha Hegde <[e-mail]>]

Hi Mach,

Thanks for the review.
Pls see inline ...


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-----Original Message-----
From: Mach Chen <[e-mail]> 
Sent: Wednesday, June 2, 2021 9:29 AM
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Subject: MPLS-RT review on draft-ninan-mpls-spring-inter-domain-oam-02

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Hi,

I am selected as a MPLS-RT reviewer of draft-ninan-mpls-spring-inter-domain-oam.

After review, I think the problem that the draft is trying to address is valid and useful. The solution is overall workable. My comments are mainly about Type 3 and Type 4 segment sub-TLV, I think it's better to address these comments before the adoption.
<Shraddha> Sure.

Type 3 and 4 sub-TLVs are supposed to be used when the headend/PMS does not have the labels or SRGB information of the remote nodes,
<Shraddha> yes because  these remote nodes lie in a different domain and SRGB information may not be available
at the headend in some cases.

 and assume that the receiving node (egress node) can derive the MPLS labels according to the IPv4/IPv6 addresses. 
<Shraddha> 
I will add a section with  example of multi-domain network with different SRGB and explain how Type 3 and Type 4
Segments can be used while building the return path dynamically for traceroute. The key is only the top segment has to be Type 3/Type 4 the remaining segments to be of type label. For the Top segment, label has to be derived from the SRGB of the receiving node (not someone else's) so its expected to be available.


This assumption may not hold, because given that the headend/PMS does not have the information, it is very likely that the receiving node has no the information either. So the draft should add more text to clarify the use cases of type 3, 4 sub-TLVs, or just remove them.
<shraddha> I'll add more text to describe clearly how type3/Type 4 should be used.

In addition, given type 3 and 4 have valid use case, the optional SID fields of type 3 and 4 are redundant, I think that they should be removed.
<shraddha> SIDs are optional anyway. I would prefer to keep it in order to be consistent with segment routing
path description.

Section 4,
"Below types of segment sub-TLVs are applicable for the Reverse Path
   Segment List TLV."

Should the "Reverse Path Segment List TLV" be "Return Path TLV"?
<shraddha> Good catch. I'll fix it.

Best regards,
Mach