[OSPF] Regarding the relationship between MSD and MSD (type 1)

[Xuxiaohu <[e-mail]>]

Hi Jeff,

(cced to PCE and OSPF WGs accordingly)

In my understanding, the semantics of the MSD terminology as defined in PCE-SR draft and the semantics of the MSD (type 1) terminology as defined in IGP-MSD draft are actually indicating the same capability (i.e., maximum label stack imposition depth) and therefore such capability should be protocol-agnostic and could be advertised via any protocol including but limited to PCEP, IS-IS, OSPF and BGP-LS. It just happens that PCEP only announces per-node MSD capability while IGP announces both per-node and per-link MSD capability. Therefore, it seems worthwhile to iron out the terminology inconsistency between MSD and MSD (type 1), IMHO. Please feel free to correct me if my understanding is wrong.

By the way, I'm totally not intending to object anything:) I just hope to eliminate the potential confusion about these two terminologies (e.g., MSD and MSD(type1)) or at least my confusion. 

Best regards,
Xiaohu

> -----邮件原件-----
> 发件人: Jeff Tantsura [mailto:[e-mail]]
> 发送时间: 2017年12月23日 2:50
> 收件人: Xuxiaohu; Les Ginsberg (ginsberg); Ketan Talaulikar (ketant); Christian
> Hopps; [e-mail]
> 抄送: [e-mail]; [e-mail]
> 主题: Re: 答复: 答复: [Isis-wg] WG Last Call for
> draft-ietf-isis-segment-routing-msd-07
> 
> Xiaohu,
> 
> PCEP and ISIS(OSPF) are quite different in their functionality and not meant to
> do the same thing. Wrt SR ecosystem, PCEP is optional, while IGP’s are
> mandatory.
> When it comes to a node capability, PCEP and IGP’s provide same information
> and fully aligned, however more granular, per link information is only available
> in IGPs, and this is as per design (not a bug).
> PCEP SR draft (which I’m co-author of) will be last called soon, please make
> sure you provide your comments to the PCE WG.
> 
> The intention of this thread is to last call draft-ietf-isis-segment-routing-msd,
> that has Type 1 defined and creates IANA registry for the future Types.
> I’d appreciate your comments specifically to the draft, and if you have got any
> technical objection, would be happy to address them.
> 
> Thanks!
> 
> Cheers,
> Jeff
> 
> -----Original Message-----
> From: Xuxiaohu <[e-mail]>
> Date: Thursday, December 21, 2017 at 16:42
> To: Jeff Tantsura <[e-mail]>, "Les Ginsberg (ginsberg)"
> <[e-mail]>, "Ketan Talaulikar (ketant)" <[e-mail]>,
> Christian Hopps <[e-mail]>, "[e-mail]" <[e-mail]>
> Cc: "[e-mail]" <[e-mail]>,
> "[e-mail]"
> <[e-mail]>
> Subject: 答复: 答复: [Isis-wg] WG Last Call for
> draft-ietf-isis-segment-routing-msd-07
> 
>     Jeff,
> 
>     IMHO, the MSD or the MSD(type 1) just indicates a certain label imposition
> capability which should be signaling-agnostic. More specially, the MSD or
> MSD(type1) capability could be signaled via IGP, BGP or PCEP.
> 
>     If the semantic of MSD (type 1) as defined in your IGP-MSD draft equals the
> semantics of MSD as defined in PCEP-SR draft, I believe it'd better to iron out
> such terminology inconsistency ASAP.
> 
>     Best regards,
>     Xiaohu
> 
>     > -----邮件原件-----
>     > 发件人: Jeff Tantsura [mailto:[e-mail]]
>     > 发送时间: 2017年12月22日 5:22
>     > 收件人: Xuxiaohu; Les Ginsberg (ginsberg); Ketan Talaulikar (ketant);
> Christian
>     > Hopps; [e-mail]
>     > 抄送: [e-mail]; [e-mail]
>     > 主题: Re: 答复: [Isis-wg] WG Last Call for
> draft-ietf-isis-segment-routing-msd-07
>     >
>     > Xuxiaohu,
>     >
>     > To clarify:
>     > The concept had been developed in both, in parallel, however PCEP
>     > implementation is limited (node only, PCC in question has to have PCEP
> sessions
>     > with the PCE), and this is clearly stated in the draft – if MSD is known
> from both
>     > sources (PCEP and IGP/BGP-LS) the later takes precedence. IGP drafts are
> the
>     > source of truth when it comes to semantics definitions.
> 
> 
> 
>     > Personally, I don’t see any confusion wrt name, all drafts have been
> around for
>     > quite some time, reviewed by many people, presented in academia and
>     > networking events, noone was ever confused…
>     >
>     > I’m not sure about value of your proposal either, and I’d leave the
> decision
>     > what to use to people who are the consumers of the technology, those
> who are
>     > going to implement it (at least 3 MSD implementations are on their
> ways).
>     >
>     > As the last point – we are not “considering” expanding, the draft is clear
> about
>     > the future extensions to come and encoding is done in a way to facilitate
> such
>     > extensions.
>     > This is the working group last call for the draft, not a discussion whether
> we
>     > should proceed with the technology:
>     > If you see any technical problems with the solution proposed – I’d be
> the first
>     > to listen to you and address them!
>     >
>     > Happy holidays!
>     >
>     > Cheers,
>     > Jeff
>     >
>     > -----Original Message-----
>     > From: Xuxiaohu <[e-mail]>
>     > Date: Wednesday, December 20, 2017 at 18:40
>     > To: "Les Ginsberg (ginsberg)" <[e-mail]>, "Ketan Talaulikar
> (ketant)"
>     > <[e-mail]>, Christian Hopps <[e-mail]>,
> "[e-mail]"
>     > <[e-mail]>
>     > Cc: "[e-mail]" <[e-mail]>,
>     > "[e-mail]"
>     > <[e-mail]>
>     > Subject: 答复: [Isis-wg] WG Last Call for
> draft-ietf-isis-segment-routing-msd-07
>     > Resent-From: <[e-mail]>
>     > Resent-To: <[e-mail]>, <[e-mail]>,
>     > <[e-mail]>, <[e-mail]>
>     > Resent-Date: Wed, 20 Dec 2017 18:40:16 -0800 (PST)
>     >
>     >     Hi Les,
>     >
>     >     If I understand it correctly, the MSD concept was originated from
>     > (https://tools.ietf.org/html/draft-ietf-pce-segment-routing-11#page-7) as
>     > described below:
>     >
>     >     "The "Maximum SID Depth" (1
>     >        octet) field (MSD) specifies the maximum number of SIDs (MPLS
> label
>     >        stack depth in the context of this document) that a PCC is
> capable of
>     >        imposing on a packet."
>     >
>     >     Before considering expanding the semantics of the MSD concept as
> defined
>     > in the above PCE-SR draft, how about first considering renaming the
> capability
>     > of imposing the maximum number of labels so as to eliminate possible
>     > confusions, e.g., Writable Label-stack Depth (WLD) as opposed to the
> Readable
>     > Label-stack Depth (RLD) as defined in
>     > (https://tools.ietf.org/html/draft-ietf-ospf-mpls-elc) and
>     > (https://tools.ietf.org/html/draft-ietf-isis-mpls-elc) ?
>     >
>     >     Best regards,
>     >     Xiaohu
>     >
>     >     > -----邮件原件-----
>     >     > 发件人: Isis-wg [mailto:[e-mail]] 代表 Les
> Ginsberg
>     > (ginsberg)
>     >     > 发送时间: 2017年12月21日 4:02
>     >     > 收件人: Ketan Talaulikar (ketant); Christian Hopps;
> [e-mail]
>     >     > 抄送: [e-mail];
> [e-mail]
>     >     > 主题: Re: [Isis-wg] WG Last Call for
> draft-ietf-isis-segment-routing-msd-07
>     >     >
>     >     > Ketan -
>     >     >
>     >     > Thanx for the comments.
>     >     > I think we do want to allow MSD support for values other than
> imposition
>     >     > values. We will revise the text so we are not restricted to only
> imposition
>     > cases.
>     >     >
>     >     >   Les
>     >     >
>     >     >
>     >     > > -----Original Message-----
>     >     > > From: Ketan Talaulikar (ketant)
>     >     > > Sent: Wednesday, December 20, 2017 1:51 AM
>     >     > > To: Christian Hopps <[e-mail]>; [e-mail]
>     >     > > Cc: [e-mail];
> [e-mail]
>     >     > > Subject: RE: [Isis-wg] WG Last Call for
>     >     > > draft-ietf-isis-segment-routing-msd-07
>     >     > >
>     >     > > Hello,
>     >     > >
>     >     > > I support this document and would like to ask the authors and
> WG to
>     >     > > consider if we can expand the scope of this draft to not just
>     >     > > "imposition" of the SID stack but also other similar limits related
> to
>     > other
>     >     > actions (e.g.
>     >     > > reading, processing, etc.). With Segment Routing, we are coming
> across
>     >     > > various actions that nodes need to do with the SID stack for
> different
>     >     > > purposes and IMHO it would be useful to extend the MSD ability
> to
>     >     > > cover those as they arise.
>     >     > >
>     >     > > Thanks,
>     >     > > Ketan
>     >     > >
>     >     > > -----Original Message-----
>     >     > > From: Isis-wg [mailto:[e-mail]] On Behalf Of
> Christian
>     >     > > Hopps
>     >     > > Sent: 20 December 2017 14:03
>     >     > > To: [e-mail]
>     >     > > Cc: [e-mail];
> [e-mail]
>     >     > > Subject: [Isis-wg] WG Last Call for
>     >     > > draft-ietf-isis-segment-routing-msd-07
>     >     > >
>     >     > >
>     >     > > The authors have asked for and we are starting a WG Last Call on
>     >     > >
>     >     > >
> https://datatracker.ietf.org/doc/draft-ietf-isis-segment-routing-msd/
>     >     > >
>     >     > > which will last an extended 4 weeks to allow for year-end PTO
> patterns.
>     >     > >
>     >     > > An IPR statement exists:
>     >     > >
>     >     > >
>     >     > >
> https://datatracker.ietf.org/ipr/search/?submit=draft&id=draft-ietf-is
>     >     > > is-
>     >     > > segment-routing-msd
>     >     > >
>     >     > > Authors please reply to the list indicating whether you are aware
> of
>     >     > > any
>     >     > > *new* IPR.
>     >     > >
>     >     > > Thanks,
>     >     > > Chris.
>     >     > >
>     >     > > _______________________________________________
>     >     > > Isis-wg mailing list
>     >     > > [e-mail]
>     >     > > https://www.ietf.org/mailman/listinfo/isis-wg
>     >     >
>     >     > _______________________________________________
>     >     > Isis-wg mailing list
>     >     > [e-mail]
>     >     > https://www.ietf.org/mailman/listinfo/isis-wg
>     >
>     >
> 
> 
>