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

[Mach Chen <[e-mail]>]

Hi Eric,

Yes, I am afraid that is the case.

Best regards,
Mach

> -----Original Message-----
> From: Eric Gray [mailto:[e-mail]]
> Sent: Friday, January 8, 2021 10:51 PM
> To: Mach Chen <[e-mail]>; Loa Andersson <[e-mail]>; Greg
> Mirsky <[e-mail]>
> Cc: mpls-chairs <[e-mail]>; mpls <[e-mail]>;
> [e-mail]; Rakesh Gandhi (rgandhi)
> <rgandhi=[e-mail]>
> Subject: RE: [mpls] MPLS-RT Review of draft-gandhi-mpls-ioam-sr-04
> 
> Mach,
> 
> 	I believe that always putting the eSPL on the top of the stack pretty much
> mandates ubiquitous (non-heterogeneous) deployment of devices that
> necessarily support iOAM - correct?
> 
> --
> Eric
> 
> -----Original Message-----
> From: mpls <[e-mail]> On Behalf Of Mach Chen
> Sent: Thursday, January 7, 2021 3:09 AM
> To: Loa Andersson <[e-mail]>; Greg Mirsky <[e-mail]>
> Cc: mpls-chairs <[e-mail]>; mpls <[e-mail]>;
> [e-mail]; Rakesh Gandhi (rgandhi)
> <rgandhi=[e-mail]>
> Subject: Re: [mpls] MPLS-RT Review of draft-gandhi-mpls-ioam-sr-04
> 
> Hi Loa,
> 
> It depends where to put the (e)SPL and how to process the eSPL. If we define an
> eSPL and always put the eSPL on the top of the label stack. It means when
> sending a packet to next LSR, an eSPL will be put on the top of the stack, when
> the next LSR received the packet, the eSPL indicates iOAM related process
> needed, then pop off eSPL and process the next label that will result in
> forwarding the packet to the next LSR. When sending the packet to next LSR,
> an eSPL will be put back on the top of the stack. It just likes popping off two
> labels and pushing one label back. But this requires that all the LSRs along the
> packet MUST know how to process the eSPL, otherwise, the packet may be
> discarded.
> 
> Best regards,
> Mach
> 
> > -----Original Message-----
> > From: Loa Andersson [mailto:[e-mail]]
> > Sent: Thursday, January 7, 2021 1:13 PM
> > To: Mach Chen <[e-mail]>; Greg Mirsky
> > <[e-mail]>
> > Cc: Stewart Bryant <[e-mail]>; Rakesh Gandhi (rgandhi)
> > <rgandhi=[e-mail]>; mpls <[e-mail]>;
> > [e-mail]; mpls-chairs <[e-mail]>
> > Subject: Re: [mpls] MPLS-RT Review of draft-gandhi-mpls-ioam-sr-04
> >
> > Maach,
> >
> > If it is a requirement from iOAM to do hop by hop processing, then the
> > SPL/eSPL is a very blunt tool, there is is always a risk that the
> > (e)SPL label that indicate the special behavior is below the maximum stack
> depth that can be scanned.
> >
> > Right?
> >
> > If we create a FEC that says "this packet has a hop by hop processing
> > requirement, go find the ACH-header immediately after the label stack
> > to see what you need to do." That would not solve the immediate
> > problem but also be useful for the future.
> >
> > /Loa
> >
> >
> > On 07/01/2021 11:50, Mach Chen wrote:
> > > Hi all,
> > >
> > > IMHO, I think the key issue is that there is no hop-by-hop option in
> > > MPLS, but the iOAM requires that.
> > >
> > > There are three potential options:
> > >
> > > 1)Scan the stack and find the (e)SPL label that indicate the special
> > > behavior;
> > >
> > > 2)Introduce an (e)SPL and always keep it on the top of the label
> > > stack;
> > >
> > > 3)Use the way as Stewart suggested, a new FEC, just like the SFL;
> > >
> > > Best regards,
> > >
> > > Mach
> > >
> > > *From:*Greg Mirsky [mailto:[e-mail]]
> > > *Sent:* Thursday, January 7, 2021 11:30 AM
> > > *To:* Loa Andersson <[e-mail]>
> > > *Cc:* Stewart Bryant <[e-mail]>; Rakesh Gandhi
> > > (rgandhi) <rgandhi=[e-mail]>; mpls
> > > <[e-mail]>; [e-mail]; mpls-chairs
> > > <[e-mail]>
> > > *Subject:* 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 <[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
> > >     >
> > >     >
> > >     >
> > >     > _______________________________________________
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> > >     >
> > >
> > >     --
> > >
> > >     Loa Andersson                        email: [e-mail]
> > <mailto:[e-mail]>
> > >     Senior MPLS Expert [e-mail]
> > <mailto:[e-mail]>
> > >     Bronze Dragon Consulting             phone: [phone]
> > >
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> > >
> >
> > --
> >
> > Loa Andersson                        email: [e-mail]
> > Senior MPLS Expert                          [e-mail]
> > Bronze Dragon Consulting             phone: [phone]
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