Re: [mpls] RtgDir review: draft-ietf-mpls-tp-rosetta-stone-12.txt

[Alexander Vainshtein <[e-mail]>]

Greg,
Lots of thanks for an important comment.

Regarding your example: my personal interpretation of 5654 is like following:
- Co-routed bidirectional LSPs MAY be protected using bi-directional protection schemes but MUST NOT be protected using unidirectional ones
- Associated bidirectional LSPs MAY be protected using both unidirectional and bi-directional protection schemes

Does this match your understanding?

Regards,
     Sasha

> -----Original Message-----
> From: Gregory Mirsky [mailto:[e-mail]]
> Sent: Monday, October 14, 2013 9:23 AM
> To: Bhatia, Manav (Manav); Alexander Vainshtein
> Cc: [e-mail]; [e-mail]; draft-ietf-mpls-tp-rosetta-
> [e-mail]; [e-mail]
> Subject: RE: RtgDir review: draft-ietf-mpls-tp-rosetta-stone-12.txt
> 
> Hi Manav,
> I do feel that "fate sharing" already has certain interpretation in the industry.
> Difference in, for example, protection between co-routed and associated bi-
> directional LSPs doesn't seem not to be described by "fate sharing". I think of it
> as in co-routed case LSP protected as a single entity while in associated case
> each direction of LSP is protected independently of the other.
> 
> 	Regards,
> 		Greg
> 
> -----Original Message-----
> From: [e-mail] [mailto:[e-mail]] On Behalf Of
> Bhatia, Manav (Manav)
> Sent: Sunday, October 13, 2013 10:26 PM
> To: Alexander Vainshtein
> Cc: [e-mail]; [e-mail]; draft-ietf-mpls-tp-rosetta-
> [e-mail]; [e-mail]
> Subject: Re: [mpls] RtgDir review: draft-ietf-mpls-tp-rosetta-stone-12.txt
> 
> Sasha,
> 
> I think the confusion is over what we mean by "fate sharing".
> 
> To me, if the forward path is torn down for some reason, and that results in the
> backward path being torn down as well, then they inextricably "share the fate".
> 
> If the path of the forward LSP changes because of an IGP trigger, then the
> backward LSP changes too in case of co-routed bidirectional LSPs. However, this
> isn't true in case of Associated bidirectional LSPs. Similarly, an IGP change (or a
> network event -- link/node flap, link/node down) will always result in both
> directions changing their path in case of co-routed bidirectional LSPs. This
> doesn't happen in case of Associated bidirectional LSPs. Its this difference that
> I wanted the authors to highlight as part of my review comment.
> 
> If you think "fate sharing" is not the most appropriate term then you can
> suggest something else as long as you believe its something that ought to be
> mentioned.
> 
> Cheers, Manav
> 
> > -----Original Message-----
> > From: Alexander Vainshtein [mailto:[e-mail]]
> > Sent: Monday, October 14, 2013 9:37 AM
> > To: Bhatia, Manav (Manav)
> > Cc: [e-mail];
> > [e-mail];
> > [e-mail]; [e-mail]
> > Subject: RE: RtgDir review: draft-ietf-mpls-tp-rosetta-stone-12.txt
> >
> >
> > Manav,
> > Lots of thanks for a prompt response.
> >
> > I must admit that I've mssed the text in 5960 to which you refer.
> >
> > The original definition, to the best of my understanding, is
> > in Section 1.2.2. of RFC 5654 and says something else:
> >
> >
> >    Co-routed Bidirectional path: A path where the forward and backward
> >    directions follow the same route (links and nodes) across the
> >    network.  Both directions are setup, monitored and protected as a
> >    single entity.  A transport network path is typically co-routed.
> >
> > To me this means that if one of the directions of the
> > co-routed bi-directional path fails to convey traffic, the
> > monitoring mechanisms will report the entire bi-directional
> > path as failed.
> >
> > To the best of my recollection when I=D to become RFC 5960
> > has been discussed I've asked the authors of RFC 5960 whether
> > the pairing between two directions of a co-routed
> > bi-directional MPLS-TP LSP in a transit LSR is limited to OAM
> > processing, and they (or one of them) have confirmed that
> > this is indeed so.
> >
> > I wonder whether this can be interpreted as "fate-sharing".
> >
> > Regards,
> >      Sasha
> >
> > ________________________________________
> > From: Bhatia, Manav (Manav) [[e-mail]]
> > Sent: Monday, October 14, 2013 4:21 AM
> > To: Alexander Vainshtein
> > Cc: [e-mail];
> > [e-mail];
> > [e-mail]; [e-mail]
> > Subject: RE: RtgDir review: draft-ietf-mpls-tp-rosetta-stone-12.txt
> >
> > Hi Sasha,
> >
> > RFC 5960 that describes the MPLS-TP data plane says the following:
> >
> > A point-to-point co-routed bidirectional LSP is a
> > point-to-point associated bidirectional LSP with the
> > additional constraint that its two unidirectional component
> > LSPs in each direction follow the same path (in terms of both
> > nodes and links).  An important property of co-routed
> > bidirectional LSPs is that their unidirectional component
> > LSPs share fate.
> >
> > Am I missing something?
> >
> > Cheers, Manav
> >
> >
> > > -----Original Message-----
> > > From: Alexander Vainshtein [mailto:[e-mail]]
> > > Sent: Sunday, October 13, 2013 9:46 PM
> > > To: Bhatia, Manav (Manav)
> > > Cc: [e-mail];
> > > [e-mail];
> > > [e-mail]; [e-mail]
> > > Subject: RE: RtgDir review: draft-ietf-mpls-tp-rosetta-stone-12.txt
> > >
> > > Manav and all,
> > > Regarding one of the nits you've identified:
> > > "it would be useful to mention that an important property
> > of co-routed
> > > bidirectional path is that the forward and backward
> > directions share
> > > fate."
> > >
> > > IMHO and FWIW this is not correct. To the best of my
> > understanding the
> > > two directions of an MPLS-TP co-routed bi-directional path share
> > > lifespan (i.e.,they are set up and torn down in a single
> > management or
> > > control plane operation).
> > > But they do not share fate, as can be seen from the following
> > > examples:
> > >
> > > 1. A unidirectiona fiber cut in one of the links used by a
> > co-routed
> > > bi-directional trail will result in traffic failur in the affected
> > > direction but not necessarily in the reverse one
> > >
> > > 2. Consider the case when one of entries the ILM in one of
> > the transit
> > > LSRs is corruped. This will result in incorrect failure of a single
> > > label, but the rest of the labels would be handled correctly. Since
> > > co-routed bi-directional trails do not require using the
> > same label in
> > > both directions of a trail, the fate sharing would be broken.
> > > (Actually, in such a way it could be easily broken even if the same
> > > label is used on each segment of the LSP in both
> > > directions...)
> > >
> > > My 2c,
> > >      Sasha
> > >
> > >
> > >
> > > ________________________________________
> > > From: [e-mail] [[e-mail]]
> > on behalf of
> > > Bhatia, Manav (Manav) [[e-mail]]
> > > Sent: Sunday, October 13, 2013 5:55 PM
> > > To: [e-mail]
> > > Cc: [e-mail];
> > > [e-mail]; [e-mail]
> > > Subject: [RTG-DIR] RtgDir review:
> > > draft-ietf-mpls-tp-rosetta-stone-12.txt
> > >
> > > Hello,
> > >
> > > I have been selected as the Routing Directorate reviewer for this
> > > draft. The Routing Directorate seeks to review all routing or
> > > routing-related drafts as they pass through IETF last call and IESG
> > > review, and sometimes on special request.
> > > The purpose of the review is to provide assistance to the
> > Routing ADs.
> > > For more information about the Routing Directorate, please
> > > seehttp://www.ietf.org/iesg/directorate/routing.html
> > >
> > > Although these comments are primarily for the use of the
> > Routing ADs,
> > > it would be helpful if you could consider them along with any other
> > > IETF Last Call comments that you receive, and strive to
> > resolve them
> > > through discussion or by updating the draft.
> > >
> > > Document: draft-ietf-mpls-tp-rosetta-stone-12.txt
> > > Reviewer: Manav Bhatia
> > > Review Date: October 13th, 2013
> > > IETF LC End Date: October 16, 2013
> > > Intended Status: Informational
> > >
> > > Summary:  This document is basically ready for publication, but has
> > > nits that should be considered prior to publication.
> > >
> > > Comments: This document is built on top of terms already defined in
> > > different RFCs and ITU-T documents. The terms and definitions have
> > > already been reviewed so there is a trifle little that needs to be
> > > done there. Overall, the document looks good and ready for
> > > publication. Some of my comments can be
> > >
> > > Nits:
> > >
> > > o) Please expand PW in either the Abstract or Sec 3.5
> > >
> > > o) When explaining Control Plane (3.6) should we mention that it is
> > > possible to operate an MPLS-TP network without using a
> > Control Plane?
> > >
> > > o) In 3.7, it would be useful to mention that an important
> > property of
> > > co-routed bidirectional path is that the forward and backward
> > > directions share fate. Similarly, in 3.1, we should mention
> > that the
> > > forward and backward directions don't share fate.
> > >
> > > o) 3.12 in the current text doesn't look very helpful. Can it be
> > > rephrased it to something like, "The equipment management function
> > > (EMF) provides the means through which an element management system
> > > (EMS) and other managing entities manage the network
> > element function
> > > (NEF)."
> > >
> > > o) 3.13 talks about Fault cause without explaining what a
> > fault cause
> > > is. It took me some time to understand what was meant by "fault
> > > cause". Can the authors of the draft rephrase
> > > 3.13 in their own language to explain what they mean by a
> > Failure. The
> > > current definition in the draft has been picked up as-is from ITU-T
> > > G.806
> > >
> > > o) 3.14 talks about "inability of a function to perform a required
> > > action". Since this RFC-to-be is in the IETF domain, can this be
> > > rephrased to use a term like router/switch instead of a
> > more esoteric
> > > "function". This is a general comment and applies to most of the
> > > definitions that have been copied from the ITU-T documents.
> > >
> > > o) The last paragraph of 3.17 says the following:
> > >
> > > "OAM packets are subject to the same forwarding treatment
> > as the data
> > > traffic, but they are distinct from the data traffic."
> > >
> > > In what sense are the OAM packets distinct from the data traffic?
> > >
> > > o) Please include "T-PE" and "S-PE" in Sec 1.2. These have not been
> > > expanded in the document.
> > >
> > > o) Sec 3.19 uses TCM without expanding it first.
> > >
> > > o) In Sec 3.23, s/Tandem Connections/Tandem Connection
> > >
> > > o) In 3.28.3, can the following text be added:
> > >
> > > An LSP segment comprises one or more continuous hops on the path of
> > > the LSP.  [RFC5654] defines two terms.  A "segment"
> > > is a single hop along the path of an LSP, while a "concatenated
> > > segment" is more than one hop along the path of an LSP.
> > >
> > > o) In 3.31, Isn't Operations Support Systems (OSS) a more
> > common term
> > > than Operations Systems (OS)?
> > >
> > > Cheers, Manav
> > >
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