Re: [Teas] question on the topology filter draft

[Vishnu Pavan Beeram <[e-mail]>]

Jie, Hi!

Please see inline (prefixed - [Vishnu Pavan])

Regards,
-Pavan

On Mon, Nov 22, 2021 at 5:45 AM Dongjie (Jimmy) <[e-mail]> wrote:

> Hi Pavan,
>
>
>
> Thanks for your reply. Please see some further inline with [Jie #2].
>
>
>
> *From:* Vishnu Pavan Beeram [mailto:[e-mail]]
> *Sent:* Friday, November 12, 2021 2:24 PM
> *To:* Dongjie (Jimmy) <[e-mail]>
> *Cc:* Loa Andersson <[e-mail]>; TEAS WG <[e-mail]>
> *Subject:* Re: [Teas] question on the topology filter draft
>
>
>
> Jie,
>
>
>
> Please see inline [prefixed Pavan]
>
>
>
> Regards,
>
> -Pavan
>
>
>
> On Thu, Nov 11, 2021 at 12:11 PM Dongjie (Jimmy) <[e-mail]>
> wrote:
>
> Hi Pavan,
>
>
>
> Please fine some comments about topology filter and its usage inline:
>
>
>
> *From:* Teas [mailto:[e-mail]] *On Behalf Of *Vishnu Pavan
> Beeram
> *Sent:* Wednesday, November 10, 2021 8:23 PM
> *To:* Loa Andersson <[e-mail]>
> *Cc:* TEAS WG <[e-mail]>
> *Subject:* Re: [Teas] question on the topology filter draft
>
>
>
> Loa,
>
>
>
> Please see inline (prefixed VPB)
>
>
>
> Regards,
>
> -Pavan
>
>
>
>
>
> On Tue, Nov 9, 2021 at 11:57 AM Loa Andersson <[e-mail]> wrote:
>
> WG, Pavan, authors,
>
> I was cut off at the end of the queue in the wg discussion. I had a
> fairly simple question,
>
> Where the topology filter(s) defined
>
>
>
> [VPB] The term “topology filter” is being introduced in
> draft-bestbar-teas-yang-topology-filter (not aware of any other document
> where it is defined). As per this data model draft, a “topology filter” is
> a data construct that can be applied on either a native topology or a
> customized topology to produce a filtered set of topological elements. The
> native or customized topology referred to here is a TE aware topology
> [RFC8795].
>
>
>
> [Jie] Since the term “topology filter” is newly introduced in this YANG
> model draft, it would be useful to state in the document “who” is the
> consumer of this information. More specifically, who will use the topology
> filter in path or route computation.
>
>
>
>
>
> [Pavan] The consumer depends on the use-case; The to-be-added use-case
> section is expected to  have sufficient details to address this.
>
>
>
> [Jie #2] OK, would like to review the use case section when it is
> available.
>
> and what benefits do we get from
> using them?
>
>
>
> [VPB] There are a couple of use-cases that are being targeted with this
> construct.
>
>
>
> (a) Specification of topology related constraints for TE path computation
> (any setup type):
> A few examples:
> - Compute a path within a specific topology
> - Compute a path within the topology associated with a specific IGP domain
> - Compute a path within the topology learnt from a specific TE Information
> Source
> - Compute a path within the topology defined by the application of one or
> more topology-filters
> ** Say, a topology with elements that are learnt via ISIS Level-2 and
> include resource-affinity red
> ** Or, a topology with elements associated with ISIS Flex-Algo 128 and do
> not include resource-affinity blue
>
>
>
> [Jie]  In the last case, why use Flex-Algo with an additional rule of
> include-affinity blue? The include rule can be defined as part of the
> Flex-Algo.
>
>
>
> [Pavan] Good question (was expecting someone to ask this; brownie points
> are in order)! Yes, you could always place as many constraints as you want
> in your Flex-Algo definition (FAD). But we are talking about TE path
> computation profiles here -- the number of TE path computation profiles
> used in a network need not be "limited" by the number of FADs deployed in
> it. When a Flex-Algo ID is passed in as part of the computation profile of
> an SR path to a path compute engine, an implementation may merge the
> constraints in the associated FAD with "other" specified constraints and
> then come up with an appropriate path (the SIDs of the Flex-Algorithm are
> used where applicable to compress the resultant path).
>
>
>
> [Jie #2] Thanks for your explanation. My understanding is FAD is defined
> for the network nodes to perform constraint based path computation in a
> distributed manner. While the merge of constraints in FAD and “other”
> specified constraints can only be used for centralized TE path computation,
> as the merged constraints cannot be used for distributed computation by the
> network nodes which only take the constraints in FAD in consideration of
> the computation, this means the computed TE path can only be a strict
> explicit path. Is my understanding correct? IMO this loses the major
> benefit of the Flex-Algo mechanism and does not need to be based on
> Flex-Algo.
>
>
[Vishnu Pavan] For the path computation use-case example above, please
consider a TE path computation profile associated with an SR policy (this
is not to be confused with IGP computation). The SR policy TE
path-computation application may be centralized or distributed (the
topology-filter in question just needs to be available at the computing
node/element).


>
>
>
>
> And what does “resource-affinity” mean in a topology filter?
>
>
>
> Resource Affinity == Admin group ([RFC3630
> <https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/html/rfc3630__;!!NEt6yMaO-gk!Wf63bNr9BsYF3NyuMHU51LlImOftv9m46EjW6Sl_v-ePYK0WjHXlEnRjb6z3fYS2$>],
> [RFC5329
> <https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/html/rfc5329__;!!NEt6yMaO-gk!Wf63bNr9BsYF3NyuMHU51LlImOftv9m46EjW6Sl_v-ePYK0WjHXlEnRjb9gfGNqM$>],
> [RFC5305
> <https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/html/rfc5305__;!!NEt6yMaO-gk!Wf63bNr9BsYF3NyuMHU51LlImOftv9m46EjW6Sl_v-ePYK0WjHXlEnRjb33V9PD-$>]
> and [RFC7308
> <https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/html/rfc7308__;!!NEt6yMaO-gk!Wf63bNr9BsYF3NyuMHU51LlImOftv9m46EjW6Sl_v-ePYK0WjHXlEnRjb01y_A-E$>
> ]).
>
>
>
> [Jie #2] Understood, in this case Admin group maybe be a better term.
>
>
>
>
>
> (b) Specification of filter-topology associated with a Network Resource
> Partition
>
>
>
> [Jie] Topology-filter and filter-topology sounds confusing to me. How
> about simply say “specification of the topology associated with a Network
> Resource Partition”?
>
>
>
>
>
> [Pavan] Ok. I was specifying a use-case using a term that is currently
> specified in draft-ietf-teas-ietf-network-slices-05; We will address
> terminology policing comments (if any) after the use-case section is
> published in the draft.
>
>
>
> [Jie #2] OK, and agree that terminology policing and alignment is needed.
>
>
>
> Best regards,
>
> Jie
>
>
>
> Best regards,
>
> Jie
>
>
> /Loa
> --
>
> Loa Andersson                        email: [e-mail]
> Senior MPLS Expert                          [e-mail]
> Bronze Dragon Consulting             phone: [phone]
>
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