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

Hi Rajesh,

First of all, your point is specific to the slice aspect of the draft. It is not related to use of Indicators. (*)

In that context:
- I mostly agree with you on the theoretical side.
- However in practice it really depends on how many different ECMPs you have, how many slices you have, how many bits you allocate for the slicing parts (It’s very different whether you have 8 “transport” slices or 1 million), how many hops on the path, how the transit LSR is doing ECMP (e.g. how many labels, possibly how many bits it use from (each) labels…) since none of this is standardized and very platform specific, how many flows the ingress is able to “see” (or how much entropy it really has from the fields it’s looking at).

With the partial data that I have in mind, IMHO there is space to use it.

But again, my presentation in IETF 113, and hence the comments in the minutes, was related to the “Indicators” part

(*) You have not claim that, but I think it’s better to clarify this part.

Regards,
--Bruno

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From: Rajesh Pandey <simply.rpandey@gmail.com>
Sent: Thursday, March 31, 2022 11:10 AM
To: DECRAENE Bruno INNOV/NET <bruno.decraene@orange.com>
Cc: John E Drake <jdrake@juniper.net>; mpls <mpls@ietf.org>; detnet WG <detnet@ietf.org>; pals@ietf.org
Subject: Re: [Pals] [mpls] draft-decraene-mpls-slid-encoded-entropy-label-id (was RE: Please review the PALS/MPLS/DetNet Joint Session minutes)

Hi Bruno,

Yes, how the EL value has been chosen does not concern the transit node. However, the value of EL does concern transit nodes.
It doesn't break ELI/EL implementation but certainly makes it weaker.

Consider an LSR node solely relying on EL and receiving most of the traffic over LAG/single virtual interface.

- For a single LSR, 20 bits of entropy gets diluted by 40% (remaining 8 bits are the same for single flow) could cause weaker ECMP and LAG load balancing decisions.
- With multiple LSR taken into consideration, it could cause traffic polarization potentially.

Regards,
Rajesh

On Thu, Mar 31, 2022 at 1:14 PM <bruno.decraene@orange.com<mailto:bruno.decraene@orange.com>> wrote:
> - Transit  […] How the EL value has been chosen.

I meant to write : How the EL value has been chosen does not concern the transit node.

Sorry for the spam

--Bruno

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From: mpls <mpls-bounces@ietf.org<mailto:mpls-bounces@ietf.org>> On Behalf Of bruno.decraene@orange.com<mailto:bruno.decraene@orange.com>
Sent: Thursday, March 31, 2022 9:38 AM
To: John E Drake <jdrake@juniper.net<mailto:jdrake@juniper.net>>
Cc: mpls <mpls@ietf.org<mailto:mpls@ietf.org>>; detnet WG <detnet@ietf.org<mailto:detnet@ietf.org>>; pals@ietf.org<mailto:pals@ietf.org>
Subject: Re: [mpls] [Pals] draft-decraene-mpls-slid-encoded-entropy-label-id (was RE: Please review the PALS/MPLS/DetNet Joint Session minutes)

John,

Regarding existing implementations compliant with Entropy Label https://datatracker.ietf.org/doc/html/rfc6790 :
- 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”.

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

--Bruno

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From: John E Drake <jdrake@juniper.net<mailto:jdrake@juniper.net>>
Sent: Wednesday, March 30, 2022 7:13 PM
To: DECRAENE Bruno INNOV/NET <bruno.decraene@orange.com<mailto:bruno.decraene@orange.com>>
Cc: Tony Li <tony.li@tony.li<mailto:tony.li@tony.li>>; mpls <mpls@ietf.org<mailto:mpls@ietf.org>>; detnet WG <detnet@ietf.org<mailto:detnet@ietf.org>>; Andrew G. Malis <agmalis@gmail.com<mailto:agmalis@gmail.com>>; pals@ietf.org<mailto:pals@ietf.org>
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
Sent from my iPhone

On Mar 30, 2022, at 1:00 PM, bruno.decraene@orange.com<mailto:bruno.decraene@orange.com> wrote:

[External Email. Be cautious of content]

From: Tony Li <tony1athome@gmail.com<mailto:tony1athome@gmail.com>> 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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--

Thanks and Regards,

Rajesh Pandey,
CISCO Systems,
Bangalore.
Mob. +91-9448252727

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