Re: [mpls] on MIAD ADI requirement draft RE: Agenda for the MPLS Open DT 2021-10-14

Stewart Bryant <> Thu, 21 October 2021 15:24 UTC

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From: Stewart Bryant <>
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Date: Thu, 21 Oct 2021 16:24:44 +0100
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Cc: Stewart Bryant <>, "Bocci, Matthew (Nokia - GB)" <>, Haoyu Song <>, loa Andersson <>, "" <>, "" <>, "" <>, DetNet Chairs <>
To: Kireeti Kompella <>
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Subject: Re: [mpls] on MIAD ADI requirement draft RE: Agenda for the MPLS Open DT 2021-10-14
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> On 21 Oct 2021, at 15:42, Kireeti Kompella <> wrote:
> Hi Matthew,
> On Oct 18, 2021, at 01:55, Bocci, Matthew (Nokia - GB) < <>> wrote:
>> “The mechanism to indicate thatAncillary Data is present MUST operate in the context of the top of stack LSE.”
> I’m not sure what this means, except possibly, the ADI MUST NOT be the top of stack LSE.  There were some suggestions that the FAI could be at the top of stack, accompanied by some label gymnastics to get the forwarding label.  This rules that option out (which I’m happy about).
> Here’s some alternate text:
> "The mechanism to indicate that Ancillary Data is present MUST allow for simple forwarding of MPLS packets based on the top of stack LSE.  A node MAY (SHOULD?) go further, though, to find the ADI within the label stack and act upon it."

MPLS always operates in the context of the top of stack.

Sure when the FEC is IP it does some rummaging around for other information but when the FEC is not IP I don’t think it does that. It certainly should not.

By binding the operation of these new features to the ToS we avoid painting ourselves into any corners and get the option to revise or exclude the operation in the light of experience.

- Stewart