Re: [mpls] [Pals] ELI/EL for the PW

Copying the thread to MPLS to include them in the discussion.

Please will copy future discussion to MPLS on this topic.

Thanks

Stewart

On 15/11/2017 06:14, Shah, Himanshu wrote:
>
> Hi Sasha –
>
> I understand that and I do not want to belabor my point.
>
> So just to clarify my point, you can view MS-PW as “PW-LSP”
>
> with S-PE as “PW-LSR”. In that context, ELI/EL below PW label,
>
> makes sense.
>
> FAT PW RFC predates the ELI/EL, but if that was not the case,
>
> ELI/EL easily would have been used as the solution the way I describe 
> above.
>
> But that is all water under the bridge.
>
> So, let us move on.
>
> On the follow on topic on the guideline,
>
> Where we say “when both are supported ONLY ONE (ELI/EL or FAT label) 
> SHOULD be used”.
>
> Since FAT label does not protect from ECMP based on DPI beyond PW CW, 
> BOTH schemes are
>
> required since FAT label suffers same mis-ordering consequences.
>
> In addition, S-PE MUST preserve and/or regenerate ELI/EL above PW label,
>
> If WG chose to provide guidelines on how to avoid mi-ordering in the 
> presence of such switches.
>
> /Thanks,/
>
> /Himanshu/
>
> *From: *"Alexander com>" <Alexander.Vainshtein@ecitele.com>
> *Date: *Wednesday, November 15, 2017 at 1:48 PM
> *To: *"pals@ietf.org" <pals@ietf.org>, "Shah, Himanshu" <hshah@ciena.com>
> *Subject: *Re: [Pals] ELI/EL for the PW
>
> Himanshu,
>
> Of course EL/ELI can be placed anywhere in the stack. But it can only 
> be inserted if the Egress LSR for the tunnel supports it. And in MS-PW 
> each S-PE terminates the tunnel LSP.
>
> From my POV flow labels are the ONLY right mechanism for adding 
> entropy to MS-PWs end-to-end.
>
> Thump typed by Sasha Vainshtein
>
> ------------------------------------------------------------------------
>
> *From:*Shah, Himanshu <hshah@ciena.com>
> *Sent:* Wednesday, November 15, 2017 3:24:54 AM
> *To:* Alexander Vainshtein; pals@ietf.org
> *Subject:* Re: [Pals] ELI/EL for the PW
>
> Hi Shasha,
>
> You are correct about how it is written in RFC 6790.
>
> I did talk to Kireeti briefly in the hallway about placement of ELI/EL 
> and MS-PW.
>
> He also did say the same but he also said that it does not matter 
> where you place it,
>
> as far as processing of the ELI/EL, would work irrespective.
>
> MS-PW technology throws the monkey ranch.
>
> One could just support 6790 and not 6391 for PW if ELI/EL placed below 
> PW label.
>
> It solves preservation of entropy across S-PE, nicely.
>
> /Thanks,/
>
> /Himanshu/
>
> *From: *"Alexander com>" <Alexander.Vainshtein@ecitele.com>
> *Date: *Tuesday, November 14, 2017 at 8:14 PM
> *To: *"pals@ietf.org" <pals@ietf.org>, "Shah, Himanshu" <hshah@ciena.com>
> *Subject: *Re: [Pals] ELI/EL for the PW
>
> Himamshu and all,
>
> I respetfully disagree.
>
> As I see it, RFC 6790 in Section 4.2 Ingress LSR" inambiguously states 
> that EL and ELI, if used, between thr TL and "application label" (if 
> spplication lsbel is used). It also specifies, that EL and ELI are 
> only pushed on an incoming packet if the tunnel egress LSR has 
> signaled that it can handle EL on the specific tunnel LSP it terminates.
>
> To me this means that in the case of a MS-PW, EL and ELI CANNOT 
> preserved by an S-PE. Whether they can be generated by an SPE is 
> another story.
>
> FAT labels, on the contrary, are always the BoS labels and thrrfore 
> are preserved by SPEs of a MS-PW.
>
> Did I miss something substantial?
>
> Thump typed by Sasha Vainshtein
>
> ------------------------------------------------------------------------
>
> *From:*Pals <pals-bounces@ietf.org> on behalf of Shah, Himanshu 
> <hshah@ciena.com>
> *Sent:* Tuesday, November 14, 2017 5:30:13 AM
> *To:* pals@ietf.org
> *Subject:* [Pals] ELI/EL for the PW
>
> /The PALS WG discussions yesterday at the IETF100, we discussed the 
> competing/
>
> /FAT PW and ELI/EL for the PW and its fate at S-PE./
>
> //
>
> /I mentioned this at Mike but got lost in subsequent discussions./
>
> //
>
> /FAT PW label as well as ELI/EL for PW (based on microflow within PW) 
> resides/
>
> /below PW label. Thus, @ingress PE, once microflow is identified, 
> either ELI/EL/
>
> /or FAT PW label is pushed./
>
> //
>
> /@S-PE, PW label swap does not have to preserve the ELI/EL while doing 
> PW label swapping,/
>
> /BECAUSE it is already below the PW label, just like how FAT PW label 
> would be./
>
> //
>
> /I confirmed this from our data plane engineer./
>
> /(we can check with Kireeti as well)/
>
> //
>
> /I would like to know if other vendors are doing this differently??/
>
> //
>
> /Given this is true, for the switches that do DPI past PW control word 
> for ECMP, /
>
>   * /FAT PW label would suffer the same misordering as no FAT PW label/
>   * /However, ELI/EL would NOT – because of the presence of ELI/
>
> //
>
> /Thanks,/
>
> /Himanshu/
>
>
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