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

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:[email protected]]
> Sent: Saturday, July 22, 2017 6:34 AM
> To: Les Ginsberg (ginsberg)
> Cc: Tony Przygienda; Hannes Gredler ([email protected]); Greg Shepherd;
> [email protected]; [email protected] 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:[email protected]] On Behalf Of Tony Przygienda
> > Sent: Friday, July 21, 2017 5:17 AM
> > To: Toerless Eckert
> > Cc: Hannes Gredler ([email protected]); Greg Shepherd; [email protected];
> > [email protected] 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
> <[email protected]<mailto:[email protected]>> 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
> > [email protected]<mailto:[email protected]>
> > 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
> 
> --
> ---
> [email protected]