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

Hi Greg,

Please see inline [Bruno]



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From: Greg Mirsky <[email protected]>
Sent: Thursday, March 31, 2022 5:30 PM
To: Henderickx, Wim (Nokia - BE/Antwerp) <[email protected]>
Cc: John E Drake <[email protected]>; DECRAENE Bruno INNOV/NET <[email protected]>; mpls <[email protected]>; detnet WG <[email protected]>; [email protected]
Subject: Re: [mpls] [Pals] draft-decraene-mpls-slid-encoded-entropy-label-id (was RE: Please review the PALS/MPLS/DetNet Joint Session minutes)

Hi Wim,
my interpretation of bullet 4 in Section 4.2 RFC 6790 "The TTL for the EL MUST be zero to ensure that it is not used inadvertently for forwarding" leads me to believe that any other than zero value in the EL TTL field is invalid per RFC 6790.
[Bruno] « MUST be zero when sent” is how we (IETF) typically define a reserved field. Are you really saying that extending a reserved field is invalid?

Consequently, that packet MUST be dropped. If that is not breaking the existing network, please help me understand what is it.
[Bruno] No you are incorrect. Quite the contrary RFC 6790 explicity says that on the Egress “The EL's TTL MUST be ignored.” https://datatracker.ietf.org/doc/html/rfc6790#section-4.1

--Bruno

Regards,
Greg

On Wed, Mar 30, 2022 at 9:11 PM Henderickx, Wim (Nokia - BE/Antwerp) <[email protected]<mailto:[email protected]>> wrote:
John,

We have 2 cases here in my view.

  *   A node that is not upgraded with the SW capabilities to support Bruno’s extension -> will still load-balance as before and might or might not take the bits into account that would be used for the slice ID

     *   I believe we are discussing this case when we discuss “we will break existing  ELI/EL Implementations”. Let’s say even if they take the slice id bit into account, they continue to hash/load-balance on the interface set assigned.
     *   Of course this node is not slice aware as the SW is not supporting this extension, but this has is not related to “breaking existing ELI/EL implementations”.
     *   Even when I did a quick test some HW does not even take into account these bits. So in my view we don’t break existing EL/ELI implementations.
     *   We should really validate the behavior of the existing systems to see the behavior if we make such claims.

  *   A node that is upgraded with the extension of Bruno’s draft will do the right thing. This can easily be resolved with an extension in the Control plane to say which nodes support and don’t support slicing.

From: John E Drake <[email protected]<mailto:[email protected]>>
Date: Wednesday, 30 March 2022 at 22:02
To: Henderickx, Wim (Nokia - BE/Antwerp) <[email protected]<mailto:[email protected]>>, [email protected]<mailto:[email protected]> <[email protected]<mailto:[email protected]>>
Cc: mpls <[email protected]<mailto:[email protected]>>, detnet WG <[email protected]<mailto:[email protected]>>, [email protected]<mailto:[email protected]> <[email protected]<mailto:[email protected]>>
Subject: RE: [mpls] [Pals] draft-decraene-mpls-slid-encoded-entropy-label-id (was RE: Please review the PALS/MPLS/DetNet Joint Session minutes)
Wim,

I think I would term it a thought experiment.  An RFC 6790 compliant node will take the value in the EL label field and use it to select an outgoing interface.  If the value in the EL field is a slice ID, such an node will select an outgoing interface which is not necessarily part of the slice in question and that outgoing interface will be to a node which is not necessarily part of the slice in question.

Yours Irrespectively,

John



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From: Henderickx, Wim (Nokia - BE/Antwerp) <[email protected]<mailto:[email protected]>>
Sent: Wednesday, March 30, 2022 3:21 PM
To: John E Drake <[email protected]<mailto:[email protected]>>; [email protected]<mailto:[email protected]>
Cc: mpls <[email protected]<mailto:[email protected]>>; detnet WG <[email protected]<mailto:[email protected]>>; [email protected]<mailto:[email protected]>
Subject: Re: [mpls] [Pals] draft-decraene-mpls-slid-encoded-entropy-label-id (was RE: Please review the PALS/MPLS/DetNet Joint Session minutes)

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John, do you have evidence of this or is this a theoretical claim ?

From: mpls <[email protected]<mailto:[email protected]>> on behalf of John E Drake <[email protected]<mailto:[email protected]>>
Date: Wednesday, 30 March 2022 at 19:13
To: [email protected]<mailto:[email protected]> <[email protected]<mailto:[email protected]>>
Cc: mpls <[email protected]<mailto:[email protected]>>, detnet WG <[email protected]<mailto:[email protected]>>, [email protected]<mailto:[email protected]> <[email protected]<mailto:[email protected]>>
Subject: Re: [mpls] [Pals] 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, [email protected]<mailto:[email protected]> wrote:

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From: Tony Li <[email protected]<mailto:[email protected]>> 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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