[Pce] Clarification Regarding Binding SID in SR-ERO/SRv6-ERO

Mrinmoy Das <mrinmoy.ietf@gmail.com> Wed, 17 May 2023 07:32 UTC

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From: Mrinmoy Das <mrinmoy.ietf@gmail.com>
Date: Wed, 17 May 2023 13:02:21 +0530
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Subject: [Pce] Clarification Regarding Binding SID in SR-ERO/SRv6-ERO
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Hello Team,

I was reading
https://datatracker.ietf.org/doc/draft-ietf-pce-binding-label-sid/16/ and
find below sections:

6.  Binding SID in SR-ERO

   In PCEP messages, LSP route information is carried in the Explicit
   Route Object (ERO), which consists of a sequence of subobjects.
   [RFC8664] defines the "SR-ERO subobject" capable of carrying a SID as
   well as the identity of the node/adjacency (NAI) represented by the
   SID.  The NAI Type (NT) field indicates the type and format of the
   NAI contained in the SR-ERO.  In case of binding SID, the NAI MUST
   NOT be included and NT MUST be set to zero.  [RFC8664] Section 5.2.1
   specifies bit settings and error handling in the case when NT=0.

7.  Binding SID in SRv6-ERO

   [I-D.ietf-pce-segment-routing-ipv6] defines the "SRv6-ERO subobject"
   for an SRv6 SID.  Similarly to SR-ERO (Section 6), the NAI MUST NOT
   be included and the NT MUST be set to zero.  [RFC8664] Section 5.2.1
   specifies bit settings and error handling in the case when NT=0.

Suppose in a SR LSP, there is an ERO object with 3 ero-subobjects, having
MPLS labels 20, 50, 80.
Now, this LSP also has 3 binding TLV, having MPLS labels 10, 50, 75.

Now, my questions are:
1. Is the restriction mentioned in section 6 means only ERO sub-object
having MPLS label 50 will not have any NAI as the same label is present as
Binding value? Other ERO sub-objects having label 20 and 80 can have NAI as
there is no binding value same to it?
2. How does the SID/Label stack look for this LSP in example?

Thanks & Regards,