Re: [Isis-wg] [Bier] WGLC: draft-ietf-bier-isis-extensions-04

Toerless Eckert <tte@cs.fau.de> Tue, 25 July 2017 19:52 UTC

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Date: Tue, 25 Jul 2017 21:52:11 +0200
From: Toerless Eckert <tte@cs.fau.de>
To: "Les Ginsberg (ginsberg)" <ginsberg@cisco.com>
Cc: Tony Przygienda <tonysietf@gmail.com>, "Hannes Gredler (hannes@gredler.at)" <hannes@gredler.at>, Greg Shepherd <gjshep@gmail.com>, "bier@ietf.org" <bier@ietf.org>, "isis-wg@ietf.org list" <isis-wg@ietf.org>, Christian Hopps <chopps@chopps.org>
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Subject: Re: [Isis-wg] [Bier] WGLC: draft-ietf-bier-isis-extensions-04
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Thanks, Less, that would be lovely!

I didn't check the OSPF draft, if its similar state, explanatory text wold equally be appreciated.

On Sun, Jul 23, 2017 at 11:28:08PM +0000, Les Ginsberg (ginsberg) wrote:
> Toerless -
> 
> I am thinking to add a statement in Section 4.1 - something like:
> 
> "At present, IS-IS support for a given BIER domain/sub-domain is limited to a single area - or to the IS-IS L2 sub-domain."
> 
> If you believe this would be helpful I will spin a new version (subject to review/agreement from my co-authors).
> 
>    Les
> 
> 
> > -----Original Message-----
> > From: Toerless Eckert [mailto:tte@cs.fau.de]
> > Sent: Saturday, July 22, 2017 6:34 AM
> > To: Les Ginsberg (ginsberg)
> > Cc: Tony Przygienda; Hannes Gredler (hannes@gredler.at); Greg Shepherd;
> > bier@ietf.org; isis-wg@ietf.org list; Christian Hopps
> > Subject: Re: [Bier] WGLC: draft-ietf-bier-isis-extensions-04
> > 
> > Thanks Les
> > 
> > When searching various terms in the doc to figure out what happens i am not
> > sure why i missed this one.
> > 
> > But: IMHO, RFCs can not only be the minimum number of words to get a
> > running implementation. It also needs to specify what this implementation
> > intends to achieve. Otherwise its not possible to do a useful review:
> > The reviewer can to verify whether the spec will achieve what it claims to
> > achieve is there no definitionn of what it claims to achieve.
> > 
> > If i understand ISIS correctly, my reverse engineering of the intent is:
> > 
> > - BIER TLVs stay within single ISIS areas. BFIR and BFER must therefore be
> >   in the same ISIS area: There is no inter-area BIER traffic possible
> >   with this specification. This is also true for ISIS area 0.
> > 
> > - The same BIER sub-domain identifiers can be re-used
> >   across different ISIS areas without any current impact. If these BFR-IDs
> >   are non-overlapping, then this would allow in the future to create a single
> >   cross ISIS area BIER sub-domain by leaking TLVs for such a BIER sub-domain
> >   across ISIS levels. Leakage is outside the scope of this specificication.
> > 
> > I actually even would like to do the following:
> > 
> > - If BIER sub-domains are made to span multiple ISIS areas and BFR-ids
> > assignemtns
> >   are made such that all BFR-ids with the same SI are in the same ISIS ara,
> >   then it should be in the future reasonably easy to create inter-area BIER
> >   not by leaking of the BIER TLV but by having BFIR MPLS unicastBIER packets
> >   for different SIs to an appropriate L2L1 BFIR that is part of the destination
> > area/SI.
> >   (if you would use SI number that are the same as ISIS area numbers then
> >    you could probably do this without any new signaling. Not quite sure if
> >    you can today easily find L1L2 border router for another area via existing
> >    TLVs).
> > 
> >   Alas, this idea will probably be killed because of the BIER architecture
> >   intent not to engineer SI assignments in geographical fashions to
> >   minimize traffic duplication in the presence of multiple SIs.
> > 
> > Cheers
> >     Toerless
> > 
> > On Sat, Jul 22, 2017 at 06:03:53AM +0000, Les Ginsberg (ginsberg) wrote:
> > > Tony/Toerless ???
> > >
> > > There is an explicit statement as to scope:
> > >
> > > <snip>
> > > Section 4.2
> > > ???
> > >    o  BIER sub-TLVs MUST NOT be included when a prefix reachability
> > >       advertisement is leaked between levels.
> > > <end snip>
> > >
> > > Tony seems to have forgotten that we had a discussion about how BIER
> > might be supported across areas and the conclusion was we did not know
> > how to do that yet.
> > > (Sorry Tony)
> > >
> > > Note this is ???consistent??? with https://www.ietf.org/id/draft-ietf-bier-
> > ospf-bier-extensions-07.txt Section 2.5<https://www.ietf.org/id/draft-ietf-
> > bier-ospf-bier-extensions-07.txt%20Section%202.5> - which limits the
> > flooding scope of BIER information to a single area unless it can be validated
> > that the best path to the prefix with BIER info can be validated to be to a
> > router which itself advertised the BIER info. This is not something IS-IS can do
> > since a single IS-IS instance only supports one area and therefore does not
> > have the Level-1 advertisements of the originating router when that router is
> > in another area.
> > >
> > > A few more responses inline.
> > >
> > > From: BIER [mailto:bier-bounces@ietf.org] On Behalf Of Tony Przygienda
> > > Sent: Friday, July 21, 2017 5:17 AM
> > > To: Toerless Eckert
> > > Cc: Hannes Gredler (hannes@gredler.at); Greg Shepherd; bier@ietf.org;
> > > isis-wg@ietf.org list; Christian Hopps
> > > Subject: Re: [Bier] WGLC: draft-ietf-bier-isis-extensions-04
> > >
> > > Terminology is a bit nits  IMO since the doc is reading clear enough for
> > someone who read BIER & ISIS. I can reread it or Les can comment whether
> > we should tighten glossary ...
> > >
> > > With the scope I agree, that got lost and the doc should be possibly rev'ed
> > before closing LC. Yes, we flood AD wide was the agreement but something
> > mentioning that this could change in the future is good so we are forced to
> > give it some thought how that would transition ...
> > >
> > > Thinking further though, in ISIS we have a clean document really. The  BIER
> > sub-TLVs go into well defined TLVs in terms of flooding scope. Normal L1-L2
> > redistribution can be used to get the info to all needed places AFAIS. So
> > maybe nothing needs to be written. I wait for Les to chime in.
> > >
> > > OSPF I would have to look @ scopes again & think whether we need to
> > write something or maybe Peter can comment ...
> > >
> > > --- tony
> > >
> > >
> > >
> > > On Fri, Jul 21, 2017 at 8:27 AM, Toerless Eckert
> > <tte@cs.fau.de<mailto:tte@cs.fau.de>> wrote:
> > > Sorry, past the two weeks, but hopefully  benign textual comments:
> > >
> > > We tried to find an explicit statement about the scope of BIER TLVs - eg:
> > > are they meant to stay within an area, have some redistribution across
> > > areas/levels or not.
> > >
> > > Tony said WG agreement was to have these TLV be flooded across the
> > > whole ISIS domain for now (this draft). So an explicit statement to that
> > effect would
> > > be great (All BIER sub-domains TLVs are flooded across all ISIS areas/levels,
> > so they span the whole ISIS domain).
> > >
> > > Also, if future work may/should could improve on that maybe some
> > > sentence about that (i guess one could just have ISIS intra-area BIER sub-
> > domains ?).
> > >
> > > Also: Do a check about possible ambiguity of any generic terms like
> > sub-domain, level, area, topology so that reader that don't know the
> > terminology ofall protocols (ISIS, BIER) by heart can easily know which
> > protocol is referred to.
> > >
> > > [Les:] There is no mention of ???level??? in the document.
> > > The use of ???sub-domain??? is clearly always associated with ???BIER???.
> > > ???topology??? is always used as an RFC 5120 topology ??? therefore
> > clearly an IS-IS topology.
> > > There is only one use of the term ???area??? (in Section 5.1). That text
> > might deserve a bit of clarification given this might be either a Level 1 area or
> > the Level2 sub-domain. I???ll take a pass at it.
> > > (BTW ??? I am talking about IS-IS area/L2sub-domain Toerless. ???)
> > >
> > > I don???t see that any other clarification is needed ??? but Toerless ??? if
> > you can point to any specific sentences/paragraphs which you find confusing
> > - I???ll take a second look.
> > >
> > >    Les
> > >
> > >
> > > I guess there are no BIER level, area or topologies, but still makes
> > > reading easier if the doc would say "ISIS level", "ISIS area", or at
> > > least have them in the Terminology section. And probably in
> > > terminology say "domain -> in the context of this document the BIER
> > domain which is also the same as the ISIS domain"
> > > (which i hope is the correct statement, see above).
> > >
> > > Cheers
> > >     Toerless
> > >
> > > _______________________________________________
> > > BIER mailing list
> > > BIER@ietf.org<mailto:BIER@ietf.org>
> > > https://www.ietf.org/mailman/listinfo/bier
> > >
> > >
> > >
> > > --
> > > We???ve heard that a million monkeys at a million keyboards could
> > produce the complete works of Shakespeare; now, thanks to the Internet,
> > we know that is not true.
> > > ???Robert Wilensky
> > 
> > --
> > ---
> > tte@cs.fau.de