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

[Loa Andersson <[e-mail]>]

Greg,

(feeling the water) if we create a hop-by-hop FEC, that in itself could 
indicate the presence of the ACH-header, right?

/Loa

On 07/01/2021 11:30, Greg Mirsky wrote:
> 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 <[e-mail] 
> <mailto:[e-mail]>> 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=[e-mail]
>     <mailto:[e-mail]>
>      >> <mailto:rgandhi <mailto:rgandhi>=[e-mail]
>     <mailto:[e-mail]>>> 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
>      >
>      >
>      >
>      > _______________________________________________
>      > mpls mailing list
>      > [e-mail] <mailto:[e-mail]>
>      > https://www.ietf.org/mailman/listinfo/mpls
>     <https://www.ietf.org/mailman/listinfo/mpls>
>      >
> 
>     -- 
> 
>     Loa Andersson                        email: [e-mail] <mailto:[e-mail]>
>     Senior MPLS Expert [e-mail] <mailto:[e-mail]>
>     Bronze Dragon Consulting             phone: [phone]
> 
>     _______________________________________________
>     mpls mailing list
>     [e-mail] <mailto:[e-mail]>
>     https://www.ietf.org/mailman/listinfo/mpls
>     <https://www.ietf.org/mailman/listinfo/mpls>
> 

-- 

Loa Andersson                        email: [e-mail]
Senior MPLS Expert                          [e-mail]
Bronze Dragon Consulting             phone: [phone]