[mpls] Re: Discussion points for upcoming MPLS WG interim

[Tony Li <[e-mail]>]

[WG chair hat: off]

Hi Loa,

This sorta sounds like you are proposing a wholly different form of ISD, but your proposal is very unclear to me.  If this is your intent, a document would be most helpful.

Regards,
Tony


> On Feb 16, 2025, at 7:22 AM, Loa Andersson - loa at pi.nu <[e-mail]> wrote:
> 
> Working Group,
> 
> I made an addressing mistake, and the below weas only sent to Adrian, but was really intended for the entire WG.
> 
> /Loa
> 
> 
> Adrian and Joel,
> 
> If we are digging into LSE counting there are more alternatives :).
> 
> - we could assign an eSPL for PSD, and use 11 bits (TC and TTL) for the offset.
> 
> or
> 
> - we could appoint one eSPL per PSD network action type, 11 bits for offset
> 
> or
> 
> - one eSPL per combination of PSD network action types
> 
> or
> 
> - do the same for each combination of ISD and PSD
> 
> The efficiency of the above obviously depends on how many NAs we think we’ll have per packet. I have no answer to that.
> 
> I’m not particularly in favor of any of these, but sonfar I had no possibility to evaluate any of the ideas. This is one aspect where I believe “an experiment” could be useful.
> 
> /Loa
> 
> 
> On Sun, 16 Feb 2025 at 12:13, Adrian Farrel <[e-mail] <mailto:[e-mail]>> wrote:
> 
>    Hi Joel,
> 
>     > Well, since email discussion is useful to more folks than the interim
> 
>    :-)
> 
>     > I will respond to your primary question here.
>     >
>     > From where I sit, no, using an eSPL for the MNA HDR is not a good
>     > choice.  Running any kind of experiment will not tell us if using
>    a bSPL
>     > would be ffective / useful.  And from where I sit, the whole
>    point was
>     > to avoid using an eSPL.  If MNA HDR uses an eSPL, the marginal
>    value of
>     > using MNA HDR over defining new free-standing mYours,
> 
>    I'd like to untangle that a little because I think that the "should
>    it be / does it need to be experimental?" is a different question
>    from "bSPL or eSPL?"
> 
>    Your email is a little truncated, but your point appears to be that
>    the "minimal" MNA cost moves from 2 LSEs with bSPL (Format A plus
>    Format B) to 3 LSEs with eSPL, and that that increase makes the use
>    of MNA of marginal benefit compared to other approaches that could
>    be invented.
> 
>    I suppose that the marginality becomes less significant for larger
>    MNA constructs. For example, looking at draft-ietf-mpls-mna-ioam-00
>    for the ISD variant, results in Format A, Format B, and a number of
>    Format D LSEs. AFAICS there are two mandatory Format D LSEs and two
>    optional Format D LSEs. So a potential 7 LSEs with bSPL or 8 with eSPL.
> 
>    Now, I am not a hardware engineer and I am not trying to influence
>    this debate. I just want to get to the facts and then help people
>    decide bSPL or eSPL.
> 
>    My belief is that the debate over Experimental is orthogonal to this
>    discussion. It's a debate we should have, but we can make the
>    discussion of that point simpler if we first resolve the b/e discussion.
> 
>    Cheers,
>    Adrian
> 
>    On 2/15/2025 8:41 AM, Adrian Farrel wrote:
>     > Hi all,
>     >
>     > In the light of the agenda which reads...
>     >> Discuss the progress of MNA related WG documents, including:
>     >> - https://datatracker.ietf.org/doc/html/draft-ietf-mpls-mna-hdr
>    <https://datatracker.ietf.org/doc/html/draft-ietf-mpls-mna-hdr>
>     >> - https://datatracker.ietf.org/doc/draft-jags-mpls-ps-mna-hdr
>    <https://datatracker.ietf.org/doc/draft-jags-mpls-ps-mna-hdr>
>     > ...I thought I would send out a couple of questions I would like
>    to see answered.
>     >
>     > 1. Are we happy to use an eSPL for MNA?
>     > The current version of draft-ietf-mpls-mna-hdr uses an eSPL. This
>    was introduced at 09 as part of moving to Experimental. I believe
>    the reasoning was that there is no scope for an Experimental bSPL.
>     > I understand that the resulting encoding is not optimal (an eSPL
>    takes two LSEs to sign MNA, where a bSPL would only take one).
>     > But how significant is this issue?
>     > Is it something we could live with or will it make MNA completely
>    infeasible?
>     >
>     > 2. If we can accept using an eSPL, would this remove the need to
>    be Experimental?
>     > There is clearly no shortage of eSPLs (while there is a
>    considerable restriction on the available bSPLs).
>     > The abundance of eSPLs means that we can effectively version MNA
>    using a new eSPL if we find the need to make changes to MNA.
>     > That would mean that we could safely publish MNA using eSPL on
>    the Standards Track.
>     >
>     > 3. If we remain as Experimental, what is the scope of the experiment?
>     > The current draft only says...
>     >     This document
>     >     describes an experiment whose purpose is to demonstrate that
>    the MNA
>     >     can be implemented and deployed.
>     > Looking at draft-bonica-gendispatch-exp, there is a lot more that
>    it would be helpful to add.
>     >
>     > Thanks for answering in advance, or for thinking about it and
>    arriving at the meeting with opinions.
>     >
>     > Cheers,
>     > Adrian
>     >
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