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

Hi Loa, et al.,
RFC 8169 uses TTL expiration to achieve processing at each RTM-capable
node. That approach creates a state in transient nodes and may not fit with
the "no state" paradigm of the Segment Routing.
And I've got a question. AFAIK, the presence of ACH in an MPLS LSP is
indicated by GAL. Is there an intention to introduce another (E)SPL for
that?

Regards,
Greg

On Wed, Jan 6, 2021 at 7:20 PM Loa Andersson <loa@pi.nu> wrote:

> Stewart,
>
> If we want to make sure that packets are processed at evey node, is the
> new FEC complementary to the ACH-header or an alternative?
>
> /Loa
>
> On 05/01/2021 00:30, Stewart Bryant wrote:
> >
> >
> >> On 4 Jan 2021, at 14:38, Rakesh Gandhi (rgandhi)
> >> <rgandhi=40cisco.com@dmarc.ietf.org
> >> <mailto: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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> >
>
> --
>
> Loa Andersson                        email: loa@pi.nu
> Senior MPLS Expert                          loa.pi.nu@gmail.com
> Bronze Dragon Consulting             phone: +46 739 81 21 64
>
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