Re: [Pce] draft-hsd-pce-sr-p2mp-policy wiki comments and action.

Dhruv Dhody <dhruv.ietf@gmail.com> Fri, 05 March 2021 04:07 UTC

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From: Dhruv Dhody <dhruv.ietf@gmail.com>
Date: Fri, 5 Mar 2021 09:36:57 +0530
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To: Tarek Saad <tsaad=40juniper.net@dmarc.ietf.org>
Cc: "Bidgoli, Hooman (Nokia - CA/Ottawa)" <hooman.bidgoli@nokia.com>, Dhruv Dhody <dd@dhruvdhody.com>, "pce@ietf.org" <pce@ietf.org>, "pce-chairs@ietf.org" <pce-chairs@ietf.org>
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Subject: Re: [Pce] draft-hsd-pce-sr-p2mp-policy wiki comments and action.
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Hi Tarek,

Thanks for your message.

As I said to Hooman, the key is for WG to figure out if the act of
downloading the replication segment is considered a PCECC operation or a
regular stateful operation.

Since the replication segment state needs to be programmed on the leaves
and the replication node; plus coordination is needed for SID/labels
across these instructions. I lean towards PCECC.

And the argument for using CCI for PCECC operations is consistency and the
ability to reuse concepts already defined. When an implementation supports
multiple of these PCECC use cases, there will be consistency in
implementation. But this is not written in stone and if the WG decides
otherwise then that's that!

Thanks!
Dhruv

On Thu, Mar 4, 2021 at 3:25 AM Tarek Saad <tsaad=
40juniper.net@dmarc.ietf.org> wrote:

> Hi Dhuruv/WG,
>
>
>
> From the RBNFs below (extracted from the bottom of this email), the
> difference I see between the 2 proposals is that the PCE-CC approach
> requires a new P2MP CCI object just to carry the resplication-sid  (which
> can already be carried today w/mechanisms in
> [draft-ietf-pce-binding-label-sid without the CCI].
>
> Yes, both proposals I presume would work to signal the
> replication-segment. However, IMO, we need not mandate an approach
> (especially that the difference below is minimal and most vendors already
> have support for the “current” proposal). Let me know, and apologies if I
> misunderstood the proposals below.
>
>
>
> >>
>
> *Current:*
>
>    <Common Header>
>    [<SRP>]
>    <LSP>
>    [<replication-sid>] as described in
> [draft-sivabalan-pce-binding-label-sid]
>  [(<PATH-ATTRIB><ERO>)...]
>
> *CCI-Object:*
>
>    <Common Header>
>    <SRP>
>    [<LSP>] <- not included for shared case
>    <CCI> <- you can carry the replication-sid as TE-binding as a TLV here
>    [(<PATH-ATTRIB><ERO>)...] <- this is a list
>
> To Recap
> - you needed ERO and PATH-ATTRIB and you get that here!
> - the unit of signaling is a programming instruction and not a Path for
> the above case!
> - aligns with other use cases in PCEP
>
> <<
>
>
>
> Regards,
>
> Tarek
>
>
>
> On 2/28/21, 5:24 PM, "Pce on behalf of Bidgoli, Hooman (Nokia -
> CA/Ottawa)" <pce-bounces@ietf.org on behalf of hooman.bidgoli@nokia.com>
> wrote:
>
>
>
> Hi Dhruv
>
>
>
> *As per draft-ietf-spring-sr-replication-segment, a replication segment
> allows a node (henceforth called as Replication Node) to replicate packets
> to a set of other nodes(called Downstream Nodes) or hosts in a Segment
> Routing Domain. *
>
>
>
> *A Replication segment can replicate a packet to directly connected
> nodes/hosts or to downstream nodes (without need for state on the transit
> routers). In some use cases replication segments can be stitch directly
> “Tree” or via a unicast segment routing domain “spraying”. In other use
> cases the replication segment can be a stand alone resource and act as a
> root and the leaf on the same node. In short a replication segment is a
> logical construct and behaves as a standalone resource, as an example it
> can be thought of as a binding SID on that particular node encoded via
> draft-ietf-pce-binding-label-sid*
>
>
>
> *This is why the authors on this draft feel a replication segment does not
> fit the PCE-CC Architecture Design, as each replication segment is really a
> head-end resource or a root that does a form of replication regardless if
> it plays the role classified as a root, bud or leaf to deliver a multicast
> service. As well, the authors view is that encoding the data in a CCI
> object does not add enhancements, however introduces further complexity
> with new identifiers to be used in message exchange, new object codepoint
> and capability allocations, when the existing proposal based on simply ERO
> encoding using already defined objects achieves the intended goals
> consistently regardless if one would consider the role a node plays in an
> overall tree. *
>
>
>
> *In addition the concept of CCI object will create further complexity for
> the protection paths of the replication segment. The replication segment
> outgoing interfaces can be protected via a single protection ERO. The ERO
> object combined with draft-koldychev-pce-multipath will create the perfect
> solution for this. *
>
>
>
> *In conclusion to repeats the original point since a replication segment
> is stand alone resource on each node (as an example a shared replication
> segment as per draft-ietf-pim-sr-p2mp-policy) with the function of
> providing a replication instruction on that node it really does not break
> the PCE-CC Architecture.*
>
>
>
> *I hope above clarifies the questions about PCE-CC decision.*
>
>
>
> *Thanks*
>
>
>
> *Hooman*
>
>
>
>
>
>
>
> *From:* Dhruv Dhody <dd@dhruvdhody.com>
> *Sent:* Thursday, February 11, 2021 9:00 PM
> *To:* Bidgoli, Hooman (Nokia - CA/Ottawa) <hooman.bidgoli@nokia.com>
> *Cc:* pce-chairs@ietf.org; pce@ietf.org
> *Subject:* Re: draft-hsd-pce-sr-p2mp-policy wiki comments and action.
>
>
>
>
>
> Hi Hooman,
>
>
>
> On Fri, Feb 12, 2021 at 5:36 AM Bidgoli, Hooman (Nokia - CA/Ottawa) <
> hooman.bidgoli@nokia.com> wrote:
>
> [Dhruv]: I feel there is some misunderstanding here. The PCECC extensions
> defined a new object called CCI, with different object-types to be defined
> for various use-cases. There is common handling for all such instructions
> and it is defined once and can be reused across multiple use cases. I
> understand that you want to use the ERO object with multi-path, and that
> *is* fine, you could in fact easily define the RBNF in such a way that both
> CCI and ERO are included for the new CCI object type for SR-P2MP.
>
> Hi Dhruv
>
> I am not sure if I understand are you suggesting we include both CCI and
> ERO as an option and vendor chooses? What benefit does this have? How would
> this improve the interop?
>
> No, I did not say "or", it is not a choice!
>
>
> In PCEP when we communicate with the head-end we use Candidate Path as the unit
> of signaling (with Policy as an association). For programming
> instructions (and not paths) we use CCI Object. New CCI Object-type for
> each use case can be defined.
>
> I think your proposal to program the replication and leaf nodes as
> (section 3.4.2) -
>
>    <Common Header>
>    [<SRP>]
>    <LSP>
>    [<replication-sid>]
>    as described in [draft-sivabalan-pce-binding-label-sid]
>    [<ERO-Attributes Object>]
>    as per [draft-koldychev-pce-multipath]
>
> * RBNF is not correct, but I get the idea! I.e. you are signaling this as
> a path on the branches and leaves :(
>
> =
>
>
> What I suggested is that for programming the branch and leaf node, we
> should use CCI as a unit of signaling and you can include the ERO and
> PATH-ATTRIB along with the CCI. Note this is a new CCI Object-type and RBNF
> can be updated for it -
>
>    <Common Header>
>    <SRP>
>    [<LSP>] <- not included for shared case
>    <CCI> <- you can carry the replication-sid as TE-binding as a TLV here
>    [(<PATH-ATTRIB><ERO>)...] <- this is a list
>
> To Recap
> - you needed ERO and PATH-ATTRIB and you get that here!
> - the unit of signaling is a programming instruction and not a Path for
> the above case!
> - aligns with other use cases in PCEP
>
> Hope I am able to explain myself clearly and this helps!
>
> Thanks!
> Dhruv
>
>
>
>
>
> Thanks
> Hooman
>
> -----Original Message-----
> From: Dhruv Dhody <dd@dhruvdhody.com>
> Sent: Thursday, February 11, 2021 5:01 AM
> To: Bidgoli, Hooman (Nokia - CA/Ottawa) <hooman.bidgoli@nokia.com>
> Cc: pce-chairs@ietf.org; pce@ietf.org
> Subject: Re: draft-hsd-pce-sr-p2mp-policy wiki comments and action.
>
> Hi Hooman,
>
> Please see inline...
>
> On Tue, Feb 9, 2021 at 8:36 PM Bidgoli, Hooman (Nokia - CA/Ottawa) <
> hooman.bidgoli@nokia.com> wrote:
> >
> > Hi Dhruv
> >
> > Much appreciate your reply, Inline
> >
> > Thanks
> > Hooman
> >
> >
> > -----Original Message-----
> > From: Dhruv Dhody <dd@dhruvdhody.com>
> > Sent: Tuesday, February 9, 2021 5:28 AM
> > To: Bidgoli, Hooman (Nokia - CA/Ottawa) <hooman.bidgoli@nokia.com>
> > Cc: pce-chairs@ietf.org; pce@ietf.org
> > Subject: Re: draft-hsd-pce-sr-p2mp-policy wiki comments and action.
> >
> > Hi Hooman,
> >
> > Apologies! Missed replying to this email...
> >
> > On Fri, Jan 22, 2021 at 12:27 AM Bidgoli, Hooman (Nokia - CA/Ottawa) <
> hooman.bidgoli@nokia.com> wrote:
> > >
> > > Dear Chairs
> > >
> > >
> > >
> > > Looking at the wiki page there was a comment on the sr-p2mp-policy
> draft.
> > >
> > >
> > >
> > > draft-hsd-pce-sr-p2mp-policy
> > >
> > > 109; More work is needed - align to PCECC, text needs to aligned to
> > > the PCE WG style
> > >
> > >
> > >
> > > The authors took an action to setup a meeting and discuss the
> alignment with PCECC farther. The final outcome of this meeting was
> unanimous agreement, by all the authors/vendors on the draft, to go forward
> with ERO object.
> > >
> > >
> >
> > As an individual I-D, it is up to the co-authors to decide the content
> of the I-D.
> >
> > The comment (and earlier discussions) was to make sure we maintain
> consistency across all our documents that we produce. RFC 8283 describes
> the PCECC architecture, where the PCE needs to interact with not only the
> head-end routers (the usual stateful/stateless PCE case) but also with the
> egress and the internal P routers. The WG has just sent the first PCECC
> extension for MPLS label allocation along the path to the IESG. For other
> use cases such as SR/SRv6 SID allocation as well as for the branch node in
> the P2MP LSP and Native-IP, all are under the PCECC umbrella. So far all
> use cases where the PCE needs to interact with other nodes beyond the
> ingress and provide instructions to them are using PCECC architecture.
> >
> > So when the PCE is interacting with the head end for SR P2MP Policy, it
> can use the usual stateful PCE extensions but when the PCE is interacting
> with the branch nodes and leaf nodes for replication segment, we strongly
> feel it should be described under the PCECC architecture. So you could use
> the ERO object for encoding the full P2MP path (and SR P2MP Policy) when
> interacting with the root node.
> > But when interacting with other nodes, use the PCECC technique i.e. a
> new CCI object type (which could be used with the ERO if needed). This
> would help you to not reinvent things as well as maintain consistency.
> > To reconfirm, the PCECC comment is related to section 3.3.3 & 4.5 only
> and not the whole document. If you still disagree please list the technical
> reason why so that the WG can evaluate them.
> >
> > HB> As I am sure you do appreciate there are many ways to skin the cat.
> TreeSID can be connected via unicast SR path and not every node needs to be
> programmed. In addition as explained the PCECC did not provide the with
> flexibility to configure backup/fast reroute paths and the current methods
> does provide that capability.
> > Again as mentioned we looked at PCECC very hard and tried to implement
> treeSID via this method but there were major short comings for backup and
> FRR paths.
> > There are multiple implementation in the field that is using the ERO
> object for treeSID with success.
> > Are the chairs suggesting that the working group is only dictating PCECC
> and is not open to any other option but PCECC for the purpose of
> programming the PCC and multicast?
> > We have been asking for adaptation since 3 IETF ago and we keep getting
> pushback because our implementation does not follow the PCECC, why is PCECC
> the only choice on the table? Why isn't the working group open to other
> options to solve the multicast requirements? Given the fact that the ERO
> has been implemented and is in the field and in multiple providers labs
> being tested with successful outcome, I think the WG should have a open
> view to this implantation. Especially when multiple vendors and providers
> (Cisco, Juniper, Nokia, Ciena, Bell Canada) to name a few have agreed to
> this implementation.
> >
> >
>
> [Dhruv]: I feel there is some misunderstanding here. The PCECC extensions
> defined a new object called CCI, with different object-types to be defined
> for various use-cases. There is common handling for all such instructions
> and it is defined once and can be reused across multiple use cases. I
> understand that you want to use the ERO object with multi-path, and that
> *is* fine, you could in fact easily define the RBNF in such a way that both
> CCI and ERO are included for the new CCI object type for SR-P2MP.
>
> Thanks!
> Dhruv
>
> > >
> > > The authors feel ERO object in addition to
> draft-koldychev-pce-multipath-04 - PCEP Extensions for Signaling Multipath
> Information (ietf.org) for backup paths is the easiest and the most
> efficient way to address the programming of a replication segment on PCC
> from to the PCE.
> > >
> > >
> > >
> > > The authors would like to move forward with the adaptation call
> please. In addition the authors are open to discuss the ERO preference in
> an interim open session with the chairs.
> > >
> > >
> >
> > The document has not been updated after 109, last we discussed this, we
> found that the document needed more work because it does not follow the way
> the PCEP extensions are usually defined. It follows a very unusual format
> (e.g. section 5) at places. It is good to provide examples but suggest it
> be done in a way that is more readable. Please follow the RBNF notations
> when specifying PCEP message changes (in a backward-compatible way). Some
> of your co-authors have vast experience in writing documents in this WG, I
> suggest taking their help. Hopefully, a more readable version will help you
> get more reviews.
> >
> > HB> sure this is cosmetics and we will follow the WG suggestion, that
> said this should not stop the adaptation call. The sooner we have
> adaptation call the sooner we can have input.
> >
> > HB> to close, as you mentioned some of the co-authors have vast
> experience in PCE WG and the same co-authors have agreed and recommended
> ERO implementation. As such I ask the chairs for adaptation call again
> ASAP. We will fix the cosmetics to be inline with WG recommendations asap.
> >
> >
> >
> > Hope this helps, and again accept our apologies for missing replying to
> this email earlier.
> >
> > Thanks!
> > Dhruv & Julien
> >
> > >
> > > Regards
> > >
> > > Hooman
> > >
> > >
> > >
> > >
>
>
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