Re: [Detnet] [mpls] Continuing with my comments on draft-decraene-mpls-slid-encoded-entropy-label-id

bruno.decraene@orange.com Fri, 21 January 2022 17:57 UTC

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From: bruno.decraene@orange.com
To: Greg Mirsky <gregimirsky@gmail.com>
CC: mpls <mpls@ietf.org>, "pals@ietf.org" <pals@ietf.org>, DetNet WG <detnet@ietf.org>
Thread-Topic: [mpls] Continuing with my comments on draft-decraene-mpls-slid-encoded-entropy-label-id
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Date: Fri, 21 Jan 2022 17:57:42 +0000
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Subject: Re: [Detnet] [mpls] Continuing with my comments on draft-decraene-mpls-slid-encoded-entropy-label-id
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Hi Greg,

Thank you for the follow up. Please see inline [Bruno2]



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From: Greg Mirsky <gregimirsky@gmail.com>
Sent: Friday, January 21, 2022 2:09 AM
To: DECRAENE Bruno INNOV/NET <bruno.decraene@orange.com>
Cc: mpls <mpls@ietf.org>; pals@ietf.org; DetNet WG <detnet@ietf.org>
Subject: Re: [mpls] Continuing with my comments on draft-decraene-mpls-slid-encoded-entropy-label-id

Hi Bruno,
thank you for your kind consideration of my comments. Please find follow-up notes in-line below under the GIM>> tag.

Regards,
Greg

On Mon, Jan 17, 2022 at 8:24 AM <bruno.decraene@orange.com<mailto:bruno.decraene@orange.com>> wrote:
Hi Greg, all

Greg, thanks for taking the time to read the draft and comment.

WG, for context, we are discussing a subset of the draft: the ability to advertise indicator as part of the existing Entropy Label TTL as described in section 2 of the draft (it's 1 page):
https://datatracker.ietf.org/doc/html/draft-decraene-mpls-slid-encoded-entropy-label-id-02#section-2

Please see inline [Bruno]



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From: mpls <mpls-bounces@ietf.org<mailto:mpls-bounces@ietf.org>> On Behalf Of Greg Mirsky
Sent: Thursday, January 13, 2022 11:41 PM
To: mpls <mpls@ietf.org<mailto:mpls@ietf.org>>; pals@ietf.org<mailto:pals@ietf.org>; DetNet WG <detnet@ietf.org<mailto:detnet@ietf.org>>
Subject: [mpls] Continuing with my comments on draft-decraene-mpls-slid-encoded-entropy-label-id

Hi Bruno, et al.
Thank you for presenting this work at the MPLS Open DT meeting today. Below please find the summary of my comments and questions with the additional thoughts that came after we've closed the call. I greatly appreciate the consideration and opinions of the authors and the group.

  *   Compatibility with nodes that support only RFC 6790.

     *   If the proposed indicators are used to signal the presence of an ISD, that seems to create a problem for an RFC6790-only node as it might not be able to process the ISD.
[Bruno]
- Draft(*) extends the use of the Entropy Label TTL field which is essentially specified as a Reserved field in RFC 6790. Hence draft is backward compatible with RFC 6790.
GIM>> I agree, that if the mechanism is limited to re-use of the TTL field of the label element that includes the entropy label, then there are no possible issues. But then, how useful is a mechanism that allows for only seven indicators of processing instructions? Of course, if the model does not support a combination of instructions, then the new field might be viewed not as a set of flags but as a scalar with each value defining a different processing type.
[Bruno2] Thank you for acknowledging that it would work. In terms of possible usages, the draft lists 3 ones in sections 3, 4 and 5.

- Draft does not specify ISD so this is out of scope of this draft. That been said:
-  You are right that before sending ISD in a new extension, the capability for the receiver/egress to support this ISD needs to be known by the sender. This is priori required by all ISD solution.
- You seemed to assume that ISD are always necessary but IMHO indicators and ISD are two different extensions and Indicators may be used without ISD extensions .e.g., cf sections 4, 5, 3 of the draft
GIM>> I agree, that in some scenarios the ability to signal processing in a label stack is sufficient and useful. Though, having a method of doing a subset of what can be done with Ancillary Data and Action indication seems like an unnecessary overlap.
[Bruno2] Thank you for the agreement. If one/a use case wants to advertise more data, it's possible to extend the proposal (actually one should be published shortly)

     *   If one of the indicators is to be used to signal the presence of the extension, that, similarly to the scenario above, might not be correctly processed by an RFC6790-only node.
[Bruno] idem

  *   Scaling

     *   If the proposed method to signal the ancillary data is used in, for example, a strict explicit routing environment, the Entropy Label is not needed. If that is the case, using the indicators, as described in the draft, seems to waste 20 bits in a label element compared to the mechanism proposed in draft-kompella-mpls-mspl4fa.
[Bruno] And for all other cases, the scaling is very good as we carry indicators with zero extra label. So the net benefit is dependent of the relative usage of strict explicit routing traffic vs traffic which can be ECMP. In my environment, the latter is much more prevalent, hence the net benefit is positive.
GIM>> I agree that there are cases and scenarios when seven indicators can solve the operator's immediate problems. Though I believe that a future-proof solution is preferable.
[Bruno2] If needed, I believe that this proposal may be extended for the use cases that would require more. I see no reason for such extension to not be equally future-proof.

Regards,
--Bruno

PS : by < draft > I mean section 2 of the draft as this is the scope of the discussion.
Regards,
-Bruno
Regards,
Greg

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