Re: [PWE3] Fwd: I-D Action: draft-shawam-pwe3-ms-pw-protection-01.txt

[Alexander Vainshtein <[e-mail]>]

Huub,

To the best of my understanding RFC 6478 is all about Static PW Status messages. 
So I am not sure what you mean when you say "use it also for PW". 

The draft actually proposes to use the PW redundancy mechanisms defined in RFC 6718 and RFC 6870 for static MS-PWs using static PW Status messages (defined in RFC 6478) in order to carry the "forwarding preference" and "request switchover" bits needed for  PW redundancy.

As for an alternative approach - I believe I have been misunderstood, probably did not present my position clearly.
I did not mean that linear protection should be presented as an optional alternative solution, just that it should be mentioned as an approach that has been considered and rejected.

To the best of my recollection, the L2VPN WG is now advancing the IPLS draft to become a Historic RFC for the same purpose - to record an idea that has been considered and rejected...
(Not sure if we can consider this as a precedent - the IPLS draft has been in limbo for more than 10 years IMO. Does age count as a special merit?:-)

Regards,
       Sasha 
Email: [e-mail]
Mobile: [phone]


> -----Original Message-----
> From: pwe3 [mailto:[e-mail]] On Behalf Of Huub van
> Helvoort
> Sent: Monday, September 29, 2014 4:34 PM
> To: [e-mail]
> Subject: Re: [PWE3] Fwd: I-D Action: draft-shawam-pwe3-ms-pw-protection-
> 01.txt
> 
> Hello,
> 
> I agree with the assessment from Andy.
> Use the mechanism in RFC6478 also for PW.
> A single approach is much less complex to provision.
> 
> Suppose there is a second approach, do _we_ have to search for it?
> Then it has to determined which is preferred/better to use as default,
> Maybe there is even a third approach...
> 
> Best regards, Huub.
> 
> > The mechanism for static PW failure handling is in RFC 6478, which is
> > also referenced in the draft.
> >
> > The primary purpose for an RFC is interoperability. If the draft
> > contains more than one approach, then one of those approaches has to
> > be mandatory to implement and use, and the other optional, otherwise
> > you can't assure interoperability. In which case, does it make sense
> > to include more than one approach and make one optional to implement?
> > And of course, if you implement both, then the primary approach has to
> > be the default one used. Then you'll also require either consistent
> > provisioning to make sure that the two ends agree on the approach
> > used, or a negotiation mechanism. It seems like you're adding a lot of
> > work to document more than one approach.
> >
> > Cheers,
> > Andy
> >
> >
> > On Mon, Sep 29, 2014 at 8:03 AM, Alexander Vainshtein
> > <[e-mail]
> > <mailto:[e-mail]>> wrote:
> >
> >     Andy,____
> >
> >     Lots of thanks for a prompt and detailed response. Please see more
> >     */inline below/*.____
> >
> >     __ __
> >
> >     Regards,____
> >
> >             Sasha ____
> >
> >     Email: [e-mail]
> >     <mailto:[e-mail]>____
> >
> >     Mobile: [phone]____
> >
> >     __ __
> >
> >     *From:*Andrew G. Malis [mailto:[e-mail]
> >     <mailto:[e-mail]>]
> >     *Sent:* Monday, September 29, 2014 2:46 PM
> >     *To:* Alexander Vainshtein
> >     *Cc:* [e-mail] <mailto:[e-mail]>
> >     *Subject:* Re: [PWE3] Fwd: I-D Action:
> >     draft-shawam-pwe3-ms-pw-protection-01.txt____
> >
> >     __ __
> >
> >     Sasha,____
> >
> >     __ __
> >
> >     Thanks for your comments. In order:____
> >
> >     __ __
> >
> >     1. No, the intended scope of this draft is Section 3.2.3 of RFC 6718
> >     and Section A.5 of RFC 6870, which describe a single-homed CE. They
> >     both use the same network model diagram. I hadn't thought it was
> >     necessary to replicate that diagram a third time, but I certainly
> >     can and will in the next revision.*/[[Sasha]] Great! /*____
> >
> >     __ __
> >
> >     2. This is actually discussed in those two sections. Basically, the
> >     entire primary PW is protected against failure by switching to the
> >     secondary PW if the primary fails for any reason. In the case of a
> >     MS-PW where the individual segments are each protected via tunnel
> >     protection, the likely cause of primary PW failure would be S-PE
> >     failure.*/[[Sasha]] I have looked up these sections again, and they
> >     say “If active/primary PW fails…”. They also mention  that typically
> >     the reason for PW failure (end-to-end) is S-PE failure. But no
> >     specific method for detecting the failure of the primary/active PW
> >     is mentioned. Maybe this should be expanded a bit in the draft with
> >     emphasis on methods that are specific to MPLS-TP and statically
> >     configured MS-PWs? /*____
> >
> >     __ __
> >
> >     3. You're actually thinking of the -00 revision of this draft. That
> >     is the approach that was presented at the Toronto PWE3 meeting, and
> >     the consensus of the discussion was that the approach in this
> >     revision should be used instead.*/[[Sasha]] Could be my mistake. And
> >     even if the approach has been changed from -00 to -01, I think that
> >     mentioning an alternative approach would be nice IMO. /*____
> >
> >     __ __
> >
> >     Cheers,____
> >
> >     Andy____
> >
> >     __ __
> >
> >     On Sun, Sep 28, 2014 at 1:03 AM, Alexander Vainshtein
> >     <[e-mail]
> >     <mailto:[e-mail]>> wrote:____
> >
> >     Andy,____
> >
> >     I've read the draft and re-read RFC 6780, and I have a couple of
> >     questions/comments that, from my point of view, should be clarified
> >     in the next revision of the draft.____
> >
> >      1. RFC 6780 and RFC 6718 describe multiple use cases for PW
> >         redundancy, including use cases with dual-homed CEs, use cases
> >         for VPLS etc. The draft refers to specific sections in these
> >         RFCs that deal with the /use case of two single-homed CEs, so I
> >         guess that this is the intended scope of the draft/. Is this
> >         assumption correct? If yes, I would suggest stating this
> >         explicitly and even including the corresponding reference
> >         network model diagram in the draft. This would not unduly expand
> >         the document while making it much more readable IMO.  (And maybe
> >         you should mention
> >         draft-cheng-pwe3-mpls-tp-dual-homing-protection a dealing with
> >         the dual-homing use cases?) ____
> >      2. RFC 6870 does not explain how S-PE failure is detected. I assume
> >         that one of the possible ways to do that could be by treating
> >         failure of the targeted/indirect LDP session between this S-PE
> >         and its adjacent PEs as S-PE failure. This is clearly not
> >         relevant in the case of statically set up MS-PWs. I would
> >         suggest adding a few words regarding possible methods for
> >         detecting S-PE failure. (As an absolute minimum, you could state
> >         that this is out of scope of the document...)____
> >      3. To the best of my recollection somebody has once posted a
> >         draft that suggested treating static MS-PWs as MPLS-TP co-routed
> >         bi-directional LSPs (which is true)and applying LSP Linear
> >         Protection for end-to-end protection of MS-PWs. This draft has
> >         long expired, but maybe the idea should be mentioned as a
> >         possible alternative approach?____
> >
> >     With these points in mind, I think that the draft is mature enough
> >     to be adopted as a WG document (even if you did not ask for that:-).
> >     ____
> >
> >     ____
> >
> >     Regards,____
> >
> >     Sasha____
> >
> >
> > ----------------------------------------------------------------------
> > --
> >
> >     *From:*pwe3 <[e-mail] <mailto:pwe3-
> [e-mail]>>
> >     on behalf of Andrew G. Malis <[e-mail]
> >     <mailto:[e-mail]>>
> >     *Sent:* Saturday, September 27, 2014 6:02 PM
> >     *To:* [e-mail] <mailto:[e-mail]>
> >     *Subject:* [PWE3] Fwd: I-D Action:
> >     draft-shawam-pwe3-ms-pw-protection-01.txt____
> >
> >     ____
> >
> >     PWE3ers, ____
> >
> >     __ __
> >
> >     Revision -00 of this draft was presented at the Toronto IETF and we
> >     received good feedback from the WG. We've updated the draft to
> >     incorporate the received comments. The draft plugs an important hole
> >     in resilience for static MS-PWs. Please review and comment to the
> >     list, it's a very quick read.____
> >
> >     __ __
> >
> >     Thanks,____
> >
> >     Andy____
> >
> >     __ __
> >
> >     ---------- Forwarded message ----------
> >     From: <[e-mail] <mailto:[e-mail]>>
> >     Date: Fri, Sep 26, 2014 at 6:05 PM
> >     Subject: I-D Action: draft-shawam-pwe3-ms-pw-protection-01.txt
> >     To: [e-mail] <mailto:[e-mail]>
> >
> >     A New Internet-Draft is available from the on-line Internet-Drafts
> >     directories.
> >
> >              Title           : S-PE Outage Protection for Static
> >     Multi-Segment Pseudowires
> >              Authors         : Andrew G. Malis
> >                                Loa Andersson
> >                                Huub van Helvoort
> >                                Jongyoon Shin
> >                                Lei Wang
> >                                Alessandro D'Alessandro
> >              Filename        : draft-shawam-pwe3-ms-pw-protection-01.txt
> >              Pages           : 5
> >              Date            : 2014-09-26
> >
> >     Abstract:
> >         In MPLS and MPLS-TP environments, statically provisioned Single-
> >         Segment Pseudowires (SS-PWs) are protected against tunnel
> >     failure via
> >         MPLS-level and MPLS-TP-level tunnel protection.  With statically
> >         provisioned Multi-Segment Pseudowires (MS-PWs), each segment of
> the
> >         MS-PW is likewise protected from tunnel failures via MPLS-level and
> >         MPLS-TP-level tunnel protection.  However, static MS-PWs are not
> >         protected end-to-end against failure of one of the switching PEs
> >         (S-PEs) along the path of the MS-PW.  This document describes how to
> >         achieve this protection by updating the existing procedures in RFC
> >         6870.
> >
> >
> >     The IETF datatracker status page for this draft is:
> >
> > https://datatracker.ietf.org/doc/draft-shawam-pwe3-ms-pw-protection/
> >
> >     There's also a htmlized version available at:
> >     http://tools.ietf.org/html/draft-shawam-pwe3-ms-pw-protection-01
> >
> >     A diff from the previous version is available at:
> >
> > http://www.ietf.org/rfcdiff?url2=draft-shawam-pwe3-ms-pw-protection-
> 01
> >
> >
> >     Please note that it may take a couple of minutes from the time of
> >     submission
> >     until the htmlized version and diff are available at tools.ietf.org
> >     <http://tools.ietf.org>.
> >
> >     Internet-Drafts are also available by anonymous FTP at:
> >     ftp://ftp.ietf.org/internet-drafts/
> 
> 
> --
> **********************************************************
> *******
>                请记住，你是独一无二的，就像其他每一个人一样
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