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Re: [mpls] MPLS-RT Review of draft-gandhi-mpls-ioam-sr-04

Stewart Bryant <stewart.bryant@gmail.com> Mon, 04 January 2021 16:31 UTC

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From: Stewart Bryant <stewart.bryant@gmail.com>
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Date: Mon, 04 Jan 2021 16:30:51 +0000
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Cc: Stewart Bryant <stewart.bryant@gmail.com>, Mach Chen <mach.chen@huawei.com>, mpls <mpls@ietf.org>, mpls-chairs <mpls-chairs@ietf.org>, "draft-gandhi-mpls-ioam-sr@ietf.org" <draft-gandhi-mpls-ioam-sr@ietf.org>
To: "Rakesh Gandhi (rgandhi)" <rgandhi=40cisco.com@dmarc.ietf.org>
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Subject: Re: [mpls] MPLS-RT Review of draft-gandhi-mpls-ioam-sr-04
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> On 4 Jan 2021, at 14:38, Rakesh Gandhi (rgandhi) <rgandhi=40cisco.com@dmarc.ietf.org> wrote:
> 
> <RG> Yes, this is similar to the entropy label where a mid-point node needs to scan the label stack to find the indicator label. We can add some text to clarify this. There is already an optimization to use a different indicator label for HbH compared to E2E case to unnecessarily avoid parsing the IOAM data fields.

The EL is entirely optional to process. It is no more than a hint to use in ECMP and there is no architectural requirement to find it to operate correctly.

If iOAM is purely a option then you could scan the stack and hope that you can reach down far enough to find it. Though there is a fight to see who gets to be the lowest label in range of the forwarding parser.

If you want to be sure that iOAM is processed HxH then you really need to run it on a new FEC with that behaviour built into the FEC. That would be the architected way of doing this in MPLS.

- Stewart

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