Re: [Detnet] [spring] 答复: SR and DetNet, draft on sr-redundancy-protection

[Gyan Mishra <[e-mail]>]

Hi  Bala'zs

As one of the Co-authors with Fan on the issue raised related to
duplication of effort of DETNET architecture service protection sub layer
providing the PREOF, sequencing function for the PRF node replication
function and PEF node elimination function, in the DETNET framework
specification  RFC 8938.

RFC 8938 excerpt

4.3 <https://datatracker.ietf.org/doc/html/rfc8938#section-4.3>.
Packet Replication, Elimination, and Ordering Functions (PREOF)

   The Controller Plane protocol solution required for managing the
   processing of PREOF is outside the scope of this document.  That
   said, it should be noted that the ability to determine, for a
   particular flow, optimal packet replication and elimination points in
   the DetNet domain requires explicit support.  There may be existing
   capabilities that can be used or extended -- for example, GMPLS end-
   to-end recovery [RFC4872
<https://datatracker.ietf.org/doc/html/rfc4872>] and GMPLS segment
recovery [RFC4873 <https://datatracker.ietf.org/doc/html/rfc4873>].


I would like to note here that the DETNET framework is flexible and as far
as the service protection sub layer and how the PEF and PRF are performed
that other solutions such as this drafts redundancy protection can be used
for service protection sub layer.

Also as far as service protection can use mechanisms that are outside of
Detnet architecture for path protection for POF function.

3.5.1.3 <https://datatracker.ietf.org/doc/html/rfc8938#section-3.5.1.3>.
Service Protection

   Service protection involves the use of multiple packet streams using
   multiple paths -- for example, 1+1 or 1:1 linear protection.  For
   DetNet, this primarily relates to packet replication and elimination
   capabilities.  MPLS offers a number of protection schemes.  MPLS
   hitless protection can be used to switch traffic to an already-
   established path in order to restore delivery rapidly after a
   failure.  Path changes, even in the case of failure recovery, can
   lead to the out-of-order delivery of data requiring POFs either
   within the DetNet service or at a high layer in the application
   traffic.  Establishment of new paths after a failure is out of scope
   for DetNet services.




Also RFC 9025 DETNET MPLS over UDP/IP centralized controller based
model for PREOF, PRF and PEF functions and sequencing see excerpt from
RFC 8938 below:


4.2 <https://datatracker.ietf.org/doc/html/rfc8938#section-4.2>.
Generic Controller Plane Considerations

   This section covers control plane considerations that are independent
   of the data plane technology used for DetNet service delivery.

   While the management plane and the control plane are traditionally
   considered separately, from a data plane perspective, there is no
   practical difference based on the origin of flow-provisioning
   information, and the DetNet architecture [RFC8655
<https://datatracker.ietf.org/doc/html/rfc8655>] refers to these
collectively as the "Controller Plane".  This document therefore does
   not distinguish between information provided by distributed control
   plane protocols (e.g., RSVP-TE [RFC3209
<https://datatracker.ietf.org/doc/html/rfc3209>] [RFC3473
<https://datatracker.ietf.org/doc/html/rfc3473>]) or centralized
   network management mechanisms (e.g., RESTCONF [RFC8040
<https://datatracker.ietf.org/doc/html/rfc8040>], YANG
   [RFC7950 <https://datatracker.ietf.org/doc/html/rfc7950>], PCEP
[PCECC <https://datatracker.ietf.org/doc/html/rfc8938#ref-PCECC>]), or
any combination thereof.  Specific
   considerations and requirements for the DetNet Controller Plane are
   discussed in Section 4.1
<https://datatracker.ietf.org/doc/html/rfc8938#section-4.1>.


Each respective data plane document also covers the control plane
   considerations for that technology.  For example, [RFC8939
<https://datatracker.ietf.org/doc/html/rfc8939>] also
   covers IP control plane normative considerations, and [DetNet-MPLS
<https://datatracker.ietf.org/doc/html/rfc8938#ref-DetNet-MPLS>]
   also covers MPLS control plane normative considerations.



>From a centralized controller management perspective as far as
instantiation of DETNET flow service protection sub layer over forwarding
plane sub layer as you can see their is some overlap.

Your point is well taken that DETNET provides its own service protection
sub layer for PREOF, however I think the DETNET framework is open to other
solutions such as this redundancy protection draft to provide a service
protection sub layer solution that is separate from the existing RFC 9025
solution.

Also the draft below provides a solution for SR-MPLS data plane but not for
SRv6.

https://datatracker.ietf.org/doc/html/draft-varga-detnet-ip-preof-00


Kind Regards

Gyan


On Wed, Jun 23, 2021 at 9:21 AM Yangfan (IP Standard) <
[e-mail]> wrote:

> Hi Bala‘zs,
>
>
>
> Not only does SR facilitate explicit routes, several WG drafts also give
> examples on the service function providing to other areas.
>
>
> https://datatracker.ietf.org/doc/html/draft-ietf-spring-sr-service-programming
>
>
> https://datatracker.ietf.org/doc/html/draft-ietf-spring-sr-replication-segment
>
>
> https://datatracker.ietf.org/doc/html/draft-ietf-spring-resource-aware-segments
>
> so I understand by leveraging redundancy segment and merging segment to
> provide PRF and PEF to DetNet is natural and acceptable.
>
>
>
> I see there is a DetNet solution for PRF and PEF in IP data plane, and
> thanks very much for submitting another contribution to elaborate the
> details.
>
> Similar like draft *IPv6-HbH-Options-for-DetNet*, the intent of the draft
> is also to bring extra capabilities from IPv6 EHs to DetNet current IP+UDP
> solution, in order to extend and progress existing work.
>
> Thanks for the discussion.
>
>
>
> Fan
>
>
>
>
>
> *发件人:* Balázs Varga A [mailto:[e-mail]]
> *发送时间:* 2021年6月18日 23:16
> *收件人:* Yangfan (IP Standard) <[e-mail]>;
> [e-mail]
> *抄送:* [e-mail]; spring <[e-mail]>
> *主题:* RE: SR and DetNet, draft on sr-redundancy-protection
>
>
>
> Hi Fan,
>
>
>
> Thank you for the clarifications. Now I see the intended behavior better.
>
>
>
> It was never a question that SR is a valuable tool to provide explicit
> routes for DetNet. Of course,
>
> that part is fully in-line with DetNet RFCs, which place those
> functionalities at the DetNet
>
> forwarding sub-layer, which is the natural location for SR.
>
>
>
> The concerns are about the functionalities that are provided by the DetNet
> service sub-layer. It
>
> looks strange to me to repeat DetNet service sub-layer functionalities by
> a tool that is naturally
>
> for the DetNet forwarding sub-layer, in particular by SR in this case.
>
>
>
> Note at the first place, that DetNet relay nodes are the ones that are
> capable to perform DetNet
>
> service sub-layer functions. DetNet relay nodes need to perform DetNet
> flow identification at the
>
> first place, which is based on 6-tuple in the case of IP data plane.
> Furthermore, DetNet already
>
> includes an IP data plane that provides sequence number for PREOF as
> specified by RFC 9025. A
>
> contribution has been submitted to describe how to leverage that for
> PREOF:
>
> https://datatracker.ietf.org/doc/draft-varga-detnet-ip-preof/.
>
>
>
> This all can be supported by SR with explicit routes in the natural way SR
> has been designed, just
>
> like any other type of traffic on top of SR, not only DetNet. Nothing
> DetNet specific needed from
>
> SR. That is, this is also fully in-line with SR today, not only DetNet.
>
>
>
> Thanks
>
> Bala'zs
>
>
>
>
>
>
>
>
>
>
>
> *From:* Yangfan (IP Standard) <[e-mail]>
> *Sent:* Saturday, June 12, 2021 8:07 AM
> *To:* Balázs Varga A <[e-mail]>;
> [e-mail]
> *Cc:* [e-mail]; spring <[e-mail]>
> *Subject:* 答复: SR and DetNet, draft on sr-redundancy-protection
>
>
>
> Hi Bala’zs,
>
> Thank you for your comments. Please see my reply inline starts with Fan1>>
>
>
>
> *发件人:* Balázs Varga A [mailto:[e-mail]
> <[e-mail]>]
> *发送时间:* 2021年6月11日 21:12
> *收件人:* [e-mail]
> *抄送:* [e-mail]; spring <[e-mail]>
> *主题:* SR and DetNet, draft on sr-redundancy-protection
>
>
>
> Hi Authors,
>
>
>
> thanks for the update of your draft, to clarify the proposed mechanism of
>
> redundancy protection.
>
>
>
> I have concerns regarding this draft as (1) the SRv6 approach does not
> follow the
>
> DetNet architecture, and (2) repeats functionalities that are provided by
> the DetNet
>
> service sub-layer but with serious limitations.
>
>
>
> (1) DetNet has defined two sub-layers: the service sub-layer and the
> forwarding
>
> sub-layer. The service sub-layer is responsible for service protection and
> the
>
> forwarding sub-layer provides forwarding paths and resource allocation on
> top of
>
> them for the DetNet flows. DetNet specifications allow to use any
> technology in
>
> the forwarding sub-layer, including Segment Routing.
>
>
>
> The SRv6 approach described in
> "draft-geng-spring-sr-redundancy-protection" breaks
>
> the clear concept of the sub-layers by mixing them up. It contradicts to
> several
>
> points at least to RFC8655 (DetNet Architecture), RFC8938 (Data Plane
> Framework)
>
> and RFC8964 (DetNet MPLS Data Plane).
>
>
>
> Fan1>> Segment routing extends IPv6 by introducing SRH extension header
> and SID programming. From the perspective of SID list in SRH, it provides
> the explicit route to IPv6 data plane in forwarding sub-layer. From the
> perspective of SID programming and Endpoint behaviors, it provides the
> packets replication and elimination in service sub-layer. So Redundancy
> segment could include the routing characteristic and service indication at
> the same time. Similar happens to Merging segment. I think this is why you
> called it breaking the concepts of two sub-layers and mixing them up.
>
> Triggered by the discussions in SPRING, I think we can define redundancy
> segment and merging segment as a functional segment without routing and
> topological semantics, and use different segment for the routing purpose.
> Thus, redundancy segment and merging segment are segments with pure service
> semantics and don’t violate the sub-layers definition in DetNet
> architecture.
>
> Besides, in RFC8655 4.1.2 DetNet data-plane overview, it says,
>
> This separation of DetNet sub-layers, while helpful, should not be
> considered a formal requirement. For example, some technologies may violate
> these strict sub-layers and still be able to deliver a DetNet service
>
> I think SRv6 could be acceptable based on this.
>
>
>
> In addition, I guess where to encapsulate meta data could be one concern.
> According to DetNet, they should be identified and encapsulated at SR edge
> node. We plan to include both possibilities in next update. To carry them
> at SR edge node would be recommended as the first choice, and thus does not
> violate DetNet architecture. Right now I still want to keep the possibility
> for redundancy segment to add meta data for some corner case.
>
>
>
> So far, I didn’t realize there are other points contradict to DetNet RFCs.
> We are very happy to discuss them.
>
>
>
> (2) The motivation for "draft-geng-spring-sr-redundancy-protection" is not
> clear especially
>
> as the SRv6 approach seems to be repeating DetNet service sub-layer
> functionalities; however,
>
> with a limited set of functionalities without any clear benefits.
>
> Fan1>> as what I said in previous email to Joel, redundancy protection
> comes from service protection specified in DetNet, but more focus on how to
> do it when Segment Routing is introduced to MPLS and IPv6. Currently,
> DetNet defines IP and MPLS data planes for DetNet in RFC8939 and RFC8964.
> There is segment routing consideration in RFC8964, but not in RFC8939. In
> our draft, we try to focus on definition in SRv6, and for MPLS-SR just
> obeys the specifications in RFC8964. It is clear that we are not repeating
> DetNet service sub-layer functionality, but to fill the gap between RFC8939
> and SRv6. If WG thinks the SR-MPLS sections are redundant, we can take
> reference from RFC8964 for simplicity in next update.
>
> I don’t think there is no clear benefit what segment routing brings to
> IP(v6). By using the redundancy protection mechanism, DetNet services
> running over SRv6 don’t rely on IP+UDP/TCP tuple to provide PREOF. The
> authors believe this draft is meaningful.
>
> Thank you for bring this topic into DetNet and SPRING. I take it as
> whether SRv6 is worth to be specified separately besides the existing
> DetNet data plane RFCs. It is a valid and important question for DetNet, we
> may need some guide from the WG.
>
> My 2 cents.
>
>
>
> Best regards,
>
> Fan
>
>
>
>
>
> Cheers
>
> Bala'zs
> _______________________________________________
> spring mailing list
> [e-mail]
> https://www.ietf.org/mailman/listinfo/spring
>
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*Gyan Mishra*

*Network Solutions A**rchitect *

*Email [e-mail] <[e-mail]>*



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