Re: [Idr] Queries on draft https://datatracker.ietf.org/doc/html/draft-ietf-idr-te-lsp-distribution-17

[Ketan Talaulikar <[e-mail]>]

Hi Abhishek,

Thanks for your email that brings up some very good questions. Please check
inline below for responses.


On Thu, Jul 28, 2022 at 3:33 PM Abhishek Chakraborty <[e-mail]>
wrote:

> Hope everyone is doing well.
>
>
>
> My queries are regarding the following flags:
>
>    1.
>    https://datatracker.ietf.org/doc/html/draft-ietf-idr-te-lsp-distribution-17#section-6.7
>
>
>
> E-Flag : Indicates that SID-List is an explicit path when set
>
>         and indicates dynamic path when clear.
>
>
>
>          C-Flag : Indicates that SID-List has been computed for a
>
>            dynamic path when set.  It is always reported as set for
>
>            explicit paths.
>
>
>
>      Does E flag only get set for Statically configured segment-list
> (non-compute) on headend router?
>

KT> Yes, but not "only" that. Please see further.


>      Does E flag includes PCE/Controller provisioned segment-lists as
> well? Because PCE/Controller provisioned segment-lists are dynamically
> provisioned by controller on the headend.
>

KT> Yes.


>      Does C flag only gets set for locally computed segment-lists? Because
> if PCE/Controller provisioned segment-lists are also dynamic paths but not
> locally computed, will this C flag
>
>                     be set for those as well?
>

KT> The draft is about reporting from the SR Policy headend. If the headend
does not see this as a dynamically computed path (e.g., if it is not
delegating computation) then the C flag won't be set.


KT> The reference here is explicit and dynamic paths per RFC9256 and not
about how they are provisioned. Specifically, please check section 5.1.


>                     What is the meaning of “It is always reported as set
> for explicit paths” in C flag?
>

KT> The SID list is pre-computed always for explicit path and hence this
flag is always set. For a dynamic path, not all paths may be computed
(e.g., if it is not the preferred/active then the path may not yet have
been computed).


>                    In case of delegation how these 2 flags will be set?
> Because the computation is done in the controller with the local constraint
> set.
>

KT> Please check if my prior response clarifies.


>
>
>    1.
>    https://datatracker.ietf.org/doc/html/draft-ietf-idr-te-lsp-distribution-17#section-6.8
>
>       *  E-Flag : Indicates the SID value is explicitly provisioned
>
>          value (locally on headend or via controller/PCE) when set and
>
>          is a dynamically resolved value by headend when clear
>
> Does this E flag on each segment means if this segment is explicitly
> configured in the segment-list locally?
>
KT> This one is not about a dynamic or explicit path but about whether the
headend is doing SID resolution. Even for an explicit path, the operator
config could be simply using a node's IP address for a Prefix-SID (Type C).
The headend needs to dynamically resolve to a SID value and so this flag is
not set. For a dynamic path, if the controller is fully resolving the SID
values and providing them to the headend then this flag would be set.


> i.e. if a segment-list is a mixture of some statically configured segments
> (non-compute) and some are computed/translated segments, then segment-list
> will be set with both segment-list C and E flags and only the non-compute
> segments will be set with E flag?
>
KT> I hope my previous comments clarify.


> Does this E flag be set on all segments of a PCE/controller provisioned
> segment-list? If yes then will such PCE/Controller provisioned
> segment-lists be marked with segment-list E flag? But then such
> segment-lists are not dynamic anymore right?
>
KT> I hope my previous comments clarify.

Thanks,
Ketan


>
>
> Thanks and Regards,
>
> Abhishek
>
>
>
> Juniper Business Use Only
>