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

"Les Ginsberg (ginsberg)" <> Sat, 22 July 2017 06:04 UTC

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From: "Les Ginsberg (ginsberg)" <>
To: Tony Przygienda <>, Toerless Eckert <>
CC: "Hannes Gredler (" <>, Greg Shepherd <>, "" <>, " list" <>, Christian Hopps <>
Thread-Topic: [Bier] WGLC: draft-ietf-bier-isis-extensions-04
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Date: Sat, 22 Jul 2017 06:03:53 +0000
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Subject: Re: [Isis-wg] [Bier] WGLC: draft-ietf-bier-isis-extensions-04
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Tony/Toerless –

There is an explicit statement as to scope:

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 Section 2.5<> - 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 [] On Behalf Of Tony Przygienda
Sent: Friday, July 21, 2017 5:17 AM
To: Toerless Eckert
Cc: Hannes Gredler (; Greg Shepherd;; 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 <<>> 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.


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).


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