Re: [Detnet] [Pals] [mpls] draft-decraene-mpls-slid-encoded-entropy-label-id (was RE: Please review the PALS/MPLS/DetNet Joint Session minutes)

[John E Drake <[e-mail]>]

Hi,

Comments inline below.

Yours Irrespectively,

John



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From: [e-mail] <[e-mail]>
Sent: Thursday, March 31, 2022 9:55 AM
To: John E Drake <[e-mail]>
Cc: Tony Li <[e-mail]>; mpls <[e-mail]>; detnet WG <[e-mail]>; Andrew G. Malis <[e-mail]>; [e-mail]
Subject: RE: [Pals] [mpls] draft-decraene-mpls-slid-encoded-entropy-label-id (was RE: Please review the PALS/MPLS/DetNet Joint Session minutes)

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John,

Please see comments inline [Bruno]



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From: John E Drake <[e-mail]<mailto:[e-mail]>>
Sent: Thursday, March 31, 2022 3:08 PM
To: DECRAENE Bruno INNOV/NET <[e-mail]<mailto:[e-mail]>>
Cc: Tony Li <[e-mail]<mailto:[e-mail]>>; mpls <[e-mail]<mailto:[e-mail]>>; detnet WG <[e-mail]<mailto:[e-mail]>>; Andrew G. Malis <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Subject: RE: [Pals] [mpls] draft-decraene-mpls-slid-encoded-entropy-label-id (was RE: Please review the PALS/MPLS/DetNet Joint Session minutes)

Hi,

Comments inline below.

Yours Irrespectively,

John



Juniper Business Use Only
From: [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>
Sent: Thursday, March 31, 2022 3:38 AM
To: John E Drake <[e-mail]<mailto:[e-mail]>>
Cc: Tony Li <[e-mail]<mailto:[e-mail]>>; mpls <[e-mail]<mailto:[e-mail]>>; detnet WG <[e-mail]<mailto:[e-mail]>>; Andrew G. Malis <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Subject: RE: [Pals] [mpls] draft-decraene-mpls-slid-encoded-entropy-label-id (was RE: Please review the PALS/MPLS/DetNet Joint Session minutes)

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John,

Regarding existing implementations compliant with Entropy Label https://datatracker.ietf.org/doc/html/rfc6790<https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/html/rfc6790__;!!NEt6yMaO-gk!Ud1zvIIaIXWqe-aLp48yFm4pbELCYyCbjygQ9tr0cs_Tdv_guebMxrHKWvddWf8$> :
- Ingress is free to use any field and any function to generate the entropy label. E.g., incoming customer physical interface and virtual interface which are not fields in the packet. The only requirement is that the EL be constant for a given flow such as this value can be used for ECMP load-balancing. I think that we’ll probably agree that the slide ID is constant for a given flow.
- Transit is mostly free to not even do anything special with EL. Assuming it uses the MPLS label for load-balancing, it’s using the value in EL either as a general label (used part of hashing multiple labels) of after recognizing the ELI and using only the EL. How the EL value has been chosen.

So I’m not seeing a theoretical way to “break existing ELI/EL Implementations”.

[JD]  As Rajesh pointed out, your proposal would dilute the effect of EL.  However, my email was discussing a different issue, viz, a down-level node would not properly handle the slice ID and would not necessarily put a packet on the correct outgoing interface.  The key selling point of your proposal is that not all nodes need to be upgraded and I was simply pointing out that if not all nodes are upgraded, your network will behave unpredictably
[Bruno] I’m not sure what you mean by “down-level node”.

[JD]  I mean a transit node that supports RFC 6790.

I will assume “downstream node”. Whether a downstream node does or does not handle the slice ID has no impact on routing/ set of outgoing interface. Set of outgoing interface is determined by the top label (transport label). Now regarding the choice of a specific outgoing interface out of the set of ECMP, there is no “correct” interface as they are equivalent. What matter is that all packets of the same flow use the same interface. This is the case whether or not the LSR support the extension: in both cases, it’s behavior is consistent across packets having the same entropy. (IOW the LSR is consistent with itself across packets/time)
The key selling point is discussed in the previous email.
No the network will not behave unpredictably in term or routing (with the exception that the choice of the outgoing interface out of the spec of ECMPs is not (easily) predictable regardless of the way load-balancing is performed.) In term of CoS (or whatever per slice treatment), LSR not supporting the slice ID (whatever its encoding) will behave like vanilla LSR. I would call this predictable, but in all cases, this is obviously the cases for all proposals.

[JD]  It is not necessarily the case that all outgoing interfaces support a given slice ID.  This means that a down-level node may select an outgoing interface that does not support the slice ID specified in the packet, which means that the packet has now left the slice

Are you aware of a specific EL compliant specification which would be broken by the new behavior? If so please be specific.

Finally, a priori the risk of affecting existing implementations seems higher with proposal doing much larger change in the MPLS Label stack, such as trying to fit generic In Stack Data in a MPLS label stack (or LSE) which has not been designed for that.

[JD]   This is simply an assertion
[Bruno] Correct. Just like your original email. At least we could agree that some proposal are doing larger change in the MPLS label by trying to fit generic In Stack Data in a MPLS label stack (or LSE) which has not been designed for that. This seem factual.

[JD]  Oopsie,  Perhaps I should have said:  if the slice ID is carried within the EL LSE label field, then the effect of EL is diluted and a down-level node may mis-route packets because it does not understand the slice ID

I’m not sure why you are not at least equally commenting on such proposals.

[JD]  In the proposals that don’t re-use EL/ELI, a down-level node will never see the new SPL and in-stack ancillary data.
[Bruno] If the egress LER does not advertise the support of the new SPL (resp. ELI) the ingress LER can send the new SPL (resp. ELI). No difference. The key difference is that today 0% LER support the new SPL while a very large portion of LER supports the ELI. New SPL support will be behind for a significant period (decade if not forever)
Transit LSR, may look at the in-stack labels (e.g. new SPL, ELI) regardless of their support (of new SPL, ELI). If they support the SPL (new or ELI) can act upon.

[JD]  If you are saying that incremental deployment of a new bSPL or a re-purposed ELI/EL are equivalent, i.e., that only the nodes that understand the new capabilities can act upon them, then I agree.  As we had indicated in our analysis, the only ELI/EL re-purposing proposal that doesn’t seem to have issues is your proposal to simply re-use the EL LSE TTL fields as indicators.  However, as Tony noted, that offers limited functionality.


--Bruno



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From: John E Drake <[e-mail]<mailto:[e-mail]>>
Sent: Wednesday, March 30, 2022 7:13 PM
To: DECRAENE Bruno INNOV/NET <[e-mail]<mailto:[e-mail]>>
Cc: Tony Li <[e-mail]<mailto:[e-mail]>>; mpls <[e-mail]<mailto:[e-mail]>>; detnet WG <[e-mail]<mailto:[e-mail]>>; Andrew G. Malis <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Subject: Re: [Pals] [mpls] draft-decraene-mpls-slid-encoded-entropy-label-id (was RE: Please review the PALS/MPLS/DetNet Joint Session minutes)

Except that putting a slice ID in the Entropy Label field will break existing  ELI/EL Implementations because their hashing of the slice ID won’t necessarily place a packet on the correct outgoing I/F
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On Mar 30, 2022, at 1:00 PM, [e-mail]<mailto:[e-mail]> wrote:

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From: Tony Li <[e-mail]<mailto:[e-mail]>> On Behalf Of Tony Li
Sent: Wednesday, March 30, 2022 4:08 PM
> [Kireeti]: suggest attending talk by Tony on danger of reusing ELI before making any decision.
https://notes.ietf.org/notes-ietf-113-pals<https://urldefense.com/v3/__https:/notes.ietf.org/notes-ietf-113-pals__;!!NEt6yMaO-gk!Sw9ofU9AyD7Z-JKwyAqMlHk5xhNLxZNMSu31Yt6-K7yh-6JehvlSPLDcqrP3gOo$>

Done. The talk raised no “danger of reusing ELI” for draft draft-decraene-mpls-slid-encoded-entropy-label-id; quite the contrary.
I quote: “claims of backward compatibility apply to draft-decraene-mpls-slid-encoded-entropy-label-id-03”. With more details on slide 18
https://datatracker.ietf.org/meeting/113/materials/slides-113-mpls-05-policy-on-mpls-special-purpose-labels-reuse-00<https://urldefense.com/v3/__https:/datatracker.ietf.org/meeting/113/materials/slides-113-mpls-05-policy-on-mpls-special-purpose-labels-reuse-00__;!!NEt6yMaO-gk!Sw9ofU9AyD7Z-JKwyAqMlHk5xhNLxZNMSu31Yt6-K7yh-6JehvlSPLDcNEC7QKk$>


Yes, the issue with this proposal is that it has no space for in-stack data and not enough space for possible expansion of additional actions.

[Bruno] There are two steps:
- This proposal allows for carrying 8 Indicators and a slice ID while been backward compatible with egress LER hance providing faster deployment with incremental benefit.
- If more in-stack data is required the proposal is extensible (e.g. draft-jags-mpls-ext-hdr) but at the cost of losing the above benefits for the ASes & uses-cases requiring more than 8 Indicators per AS or In-Stack Data.
So we can have both worlds: simple first step and extensibility for those who need it.

Independently, we also/already have the post stack data option to carry ancillary data, which may limit the need for In-Stack data extension.

--Bruno

Tony




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