Re: [Bier] draft-ietf-bier-ipv6-requirements-09

Greg Mirsky <> Wed, 25 November 2020 21:14 UTC

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From: Greg Mirsky <>
Date: Wed, 25 Nov 2020 13:14:12 -0800
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To: Tony Przygienda <>
Cc: Alvaro Retana <>, Greg Shepherd <>, BIER WG <>, Gyan Mishra <>, draft-ietf-bier-ipv6-requirements <>, "" <>, "Jeffrey (Zhaohui) Zhang" <>
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Subject: Re: [Bier] draft-ietf-bier-ipv6-requirements-09
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Dear All,
I apologize for jumping into this discussion but have someone said "OAM"? :)
I much appreciate what our co-chair (and contributor to BIER OAM) had to
say about the state of BIER OAM work. I agree with Tony's summary that our
joint efforts already created the toolset of the distinctive solutions for
BIER OAM. We've followed draft-ietf-bier-oam-requirements
<> to
define the comprehensive set of OAM mechanisms that support proactive and
on-demand failure detection and localization using both BFD and echo
request/reply. Also, as Tony mentioned, we have drafts on path MTU
discovery in the BIER environment and application of the Alternate Marking
method for the packet delay and packet loss measurement in a BIER domain.
In my opinion, the section on OAM in draft-ietf-bier-ipv6-requirements is
helpful. I have a question on the intention of the following wording:

.... by specifying a new method for the same functionality.

If there's, for example, WG draft on proactive failure detection in the
BIER network using p2mp BFD with unsolicited notifications, why would we
entertain the idea of defining a new protocol or method for the same
purpose? I think that the ability to use BIER OAM solutions as defined in
their respective drafts already accepted by the WG (and some even passed
WGLC) is the litmus test for any proposed method of realizing BIER in IPv6
network. Thus I propose the following change of Section 3.1.4
   BIER OAM tools like [I-D.ietf-bier-ping] and [I-D.ietf-bier-pmmm-oam]
   should be supported, either directly using existing methods, or by
   specifying a new method for the same functionality.  They are likely
   to be needed in normal BIER deployment for diagnostics.
   BIER OAM tools defined in WG document, for example,
   [I-D.ietf-bier-ping] and [I-D.ietf-bier-pmmm-oam],
   must be supported as defined in the respective specifications.
   of OAM BIER tools is essential for the productive operation of BIER


On Wed, Nov 18, 2020 at 11:09 PM Tony Przygienda <>

> Quick correction here as to OAM. OAM is worked on and multiple quite
> extensive & well-written drafts dealing with OAM aspects are adopted/in
> flight since quite a while (I count 4 adopted & 1 individual). BIER has
> been specifically architected with multicast OAM in mind which is
> non-trivial such as MTU discovery (we have 2 drafts for a good reason &
> discussion is pending) and dealing with OAM when we're dealing with mp2mp
> trees (which BIER basically is or can be used at). One of the reasons BIER
> found interest in the set of people that need/like it is that they were
> looking for very tight OAM guarantees in orders of microseconds and that
> without highly specific hardware designed for it is very difficult (and
> packet format, that's why OAM is first order citizen in BIER in terms of
> bits provided e.g. for marking purposes and can be found in a very specific
> offset. to support the OAM desired HW has to process and generate
> sub-microseconds trains.
> As far as I saw there was not much on the radar in terms of anything
> comparable in SRv6 OAM work beside "SID-ping" if the intention is to rely
> on SRv6 to deal with that problem. But of course I may have missed some
> draft. Even if they work on unicast OAM I may express my profound doubts
> there will be interest or focus to solve OAM for SRv6 becoming a L3
> multicast transport with the type of OAM BIER needs on top.
> As to desired OAM, I think we have an OAM requirements draft adopted with
> quite a list of industry authors since quite a bit. this draft has WG
> consensus and has to be satisfied.
> -- tony
> On Wed, Nov 18, 2020 at 7:50 PM Alvaro Retana <>
> wrote:
>> On November 19, 2020 at 3:18:58 AM, Gyan Mishra wrote:
>> Hi!
>> Just a couple of comments.
>> > On Wed, Nov 18, 2020 at 11:29 AM Jeffrey (Zhaohui) Zhang wrote:
>> ..
>> > > From: Gyan Mishra
>> > > Sent: Wednesday, November 18, 2020 10:14 AM
>> ...
>> > > > Alvaro mentioned as far as the list of requirements that they were
>> > > > fairly basic but maybe needed some more meat behind it such as the
>> > > > “support various L2 link types” but we did not specify. In previous
>> > > > versions we stated L2 agnostic and then switched to various but
>> being
>> > > > vague on which L2. Alvaro also mentioned why OAM should be a
>> > > > requirement. We may want to add a sentence on justification as to
>> why we
>> > > > picked BIER IPv6 requirements as required versus optional.
>> > >
>> > > Zzh> I actually don’t think L2 link types is a key issue. Whatever
>> modern
>> > > L2 links that an operator wants to use, it’ll need to be supported
>> both by
>> > > IPv6 and BIER, and it is as simple as adding a codepoint for the L2
>> header
>> > > to indicate whether the next header is IP/MPLS/BIER/whatever (again –
>> the
>> > > beauty of clear and independent layering).
>> > >
>> > Gyan> I don’t think Alvaro was saying there was any issue but just
>> pointing
>> > out that we did not specify which link types. We can discuss with
>> authors
>> > what link types we should add explicitly.
>> <individual hat on>
>> It was Loa, not me, who raised the point about the L2 requirement
>> being vague.  I do agree with him.  I also agree with Jeffrey on his
>> point that "modern L2 links that an operator wants to use, it’ll need
>> to be supported".  To me, this then becomes another general
>> requirement -- unless there's a special reason to add or exclude
>> something.
>> I did say that the mandatory requirements are general and broad.  For
>> example, "support the BIER architecture" is obvious, and I assume both
>> solutions do.  BTW, "deployments with BIER-incapable routers" is also
>> covered in rfc8279.
>> My comment about OAM was along the lines of the fact that there is no
>> standard BIER OAM mechanism defined.  It seems like a stretch to
>> require BIER functionality that has not been defined.  A better
>> approach might be to explain the required functionality (for example,
>> continuity, liveliness, etc.).
>> ...
>> > > Zzh> With the above consideration, I would say the “suggested next
>> steps”
>> > > in my presentation is quite reasonable.
>> > >
>> > Gyan> Let’s have the chairs and AD chime in on this thread.
>> <AD hat on.>
>> As I mentioned on the call, my opinions on this thread are as an
>> individual.  The Chairs are more than capable of providing direction
>> and don't need me for that.
>> Thanks!
>> Alvaro.
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