Re: [Teas] [Lsr] Fwd: Working Group Last Call for "Applicability of IS-IS Multi-Topology (MT) for Segment Routing based Network Resource Partition (NRP)" - draft-ietf-lsr-isis-sr-vtn-mt-06

[Joel Halpern <[e-mail]>]

Acee, I think I disagree with your request to tone down the scaling 
concerns regarding SPF calculations in the NRP scaling documents.  These 
are separate SPFs, so many of the techniques that help scale coping with 
SPF calculation related to base topology changes do not apply.  One or 
two extra SPFs is probably not a big deal.  But some of the discussion 
have been around the fact  that 8, or even 64 ode point values may not 
be enough to identify the NRPs.  Having 64 additional topologies, each 
with their own NRP calculation, seems quite problematic.  (And one 
document author suggested that operators had told him that the needed 
number was in the hundreds.  I don't understand the use case, but it is 
not for me to tell an operator "no" without a lot mor e nformation.)

Yours,

Joel

On 1/19/2024 2:04 PM, Acee Lindem wrote:
> Speaking as WG member:
>
> Hi Les,
>
> You probably saw my shepherd review of this document.
>
>> On Jan 11, 2024, at 2:33 AM, Les Ginsberg (ginsberg) <[e-mail]> wrote:
>>
>> Chongfeng –
>>   We are at the stage of last call.
>> The document has been presented and discussed previously – it is time for WG members to render their opinions.
>>   For folks who have actively followed/participated in the discussion, it is very unlikely that we will alter opinions by further discussion. Which means if you and I have different points of view it is very unlikely that I will alter your opinion and very unlikely that you will alter mine.
>> In that context, I typically do not reply when someone posts their opinion and it is different than mine. The point of last call is to get the opinions of WG members.
>>   In this case, however, I will respond with some clarifications – not in the hopes of changing your mind – but only to provide additional clarity as to why I have the opinion that I do.
>>   The use of MT in support of NRP – at whatever scale – clearly requires additional SPF calculations – which is something which is expressly identified as undesirable in draft-ietf-teas-nrp-scalability.
>> draft-ietf-teas-nrp-scalability also states (as you have pointed out) that “control plane extensions” are seen as undesirable.
> I think this needs to removed or at least softened in the NRP scaling document. The drawbacks of SPF calculations are greatly exaggerated (especially if implemented efficiently on today’s CPUs). Furthermore, it would be hypocritical to say that SPF calculations are to avoided and to then standardize features such as TI-LFA.
>
> Thanks,
> Acee
>
>
>
>
>>   Having implemented the use of MT for purposes other than supporting the reserved AFI/SAFI specific topologies specified in RFC 5120, I can tell you that there is a significant amount of “control plane work” associated with adding such support. The fact that no new protocol extensions are required is not the same as saying no new control plane work is required. I can assure you that there would be a significant amount of control plane work required.
>>   So I do see that draft-ietf-lsr-isis-sr-vtn-mt is at odds with draft-ietf-teas-nrp-scalability.
>>   Thanx for listening.
>>       Les
>>    From: Lsr <[e-mail]> On Behalf Of Chongfeng Xie
>> Sent: Wednesday, January 10, 2024 7:41 PM
>> To: Les Ginsberg (ginsberg) <ginsberg=[e-mail]>; jmh <[e-mail]>; Acee Lindem <[e-mail]>; TEAS WG <[e-mail]>; lsr <[e-mail]>
>> Subject: Re: [Lsr] [Teas] Fwd: Working Group Last Call for "Applicability of IS-IS Multi-Topology (MT) for Segment Routing based Network Resource Partition (NRP)" - draft-ietf-lsr-isis-sr-vtn-mt-06
>>    Hi Les,
>>   Thanks for your comments.
>>   This is an informational document which describes the applicability of existing IS-IS MT mechanisms for building SR based NRPs. All the normative references are either RFCs or stable WG documents. It is true that some informative references are individual documents, while they just provide additional information related to this topic, thus would not impact the stability and maturity of the proposed mechanism.
>>   The text you quoted from draft-ietf-teas-nrp-scalability are about the considerations when the number of NRP increases, how to minimize the impact to the routing protocols (e.g. IGP). While as described in the scalability considerations section of this document, the benefit and limitation of using this mechanism for NRP are analyzed, and it also sets the target scenarios of this mechanism:
>>        “The mechanism described in this document is considered useful for network scenarios in which the required number of NRP is small”
>>   Thus it is clear that this solution is not recommended for network scenarios where the number of required NRP is large.
>>   Please note section 3 of draft-ietf-teas-nrp-scalability also mentioned that:
>>         “The result of this is that different operators can choose to deploy things at different scales.”
>>   And
>>         “In particular, we should be open to the use of approaches that do not require control plane extensions and that can be applied to deployments with limited scope.”
>>    According to the above text, we believe the mechanism described in this document complies to the design principles discussed in draft-ietf-teas-nrp-scalability and provides a valid solution for building NRPs in a limited scope.
>>    Hope this solves your concerns about the maturity and scalability of this mechanism.
>>    Best regards,
>>   Chongfeng
>>    From: Les Ginsberg \(ginsberg\)
>> Date: 2024-01-11 08:21
>> To: Joel Halpern; Acee Lindem; [e-mail]; [e-mail]
>> Subject: Re: [Lsr] [Teas] Fwd: Working Group Last Call for "Applicability of IS-IS Multi-Topology (MT) for Segment Routing based Network Resource Partition (NRP)" - draft-ietf-lsr-isis-sr-vtn-mt-06
>> (NOTE: I am replying to Joel’s post rather than the original last call email because I share some of Joel’s concerns – though my opinion on the merits of the draft is very different.
>> Also, I want to be sure the TEAS WG gets to see this email.)
>>   I oppose Last Call for draft-ietf-lsr-isis-sr-vtn-mt.
>>   It is certainly true, as Joel points out, that this draft references many drafts which are not yet RFCs – and in some cases are not even WG documents. Therefore, it is definitely premature to last call this draft.
>>   I also want to point out that the direction TEAS WG has moved to recommends that routing protocols NOT be used as a means of supporting NRP.
>>   https://www.ietf.org/archive/id/draft-ietf-teas-nrp-scalability-03.html#name-scalabliity-design-principl states:
>>   “…it is desirable for NRPs to have no more than small impact (zero being preferred) on the IGP information that is propagated today, and to not required additional SPF computations beyond those that are already required.”
>>   https://www.ietf.org/archive/id/draft-ietf-teas-nrp-scalability-03.html#name-scalabliity-design-principl states:
>>   “The routing protocols (IGP or BGP) do not need to be involved in any of these points, and it is important to isolate them from these aspects in order that there is no impact on scaling or stability.”
>>   Another draft which is referenced is https://datatracker.ietf.org/doc/draft-dong-lsr-sr-enhanced-vpn/ - which is not a WG document and – based on the recommendations in draft-ietf-teas-nrp-scalability – I would argue that the IGPs should NOT be extended as proposed in this draft. So if a WG adoption call were to initiated for draft-dong-lsr-sr-enhanced-vpn, I would oppose it.
>>   This then puts draft-ietf-lsr-isis-sr-vtn-mt in the position of publishing information about a solution which the IETF is discouraging. I do not know why the IETF would want to do this.
>>   If, despite all of the above, at some point it is judged not premature to publish this draft, I think the draft should at least include statements indicating that this approach is not a recommended deployment solution.
>>      Les
>>    From: Lsr <[e-mail]> On Behalf Of Joel Halpern
>> Sent: Wednesday, January 10, 2024 3:22 PM
>> To: Acee Lindem <[e-mail]>; [e-mail]; [e-mail]
>> Subject: Re: [Lsr] [Teas] Fwd: Working Group Last Call for "Applicability of IS-IS Multi-Topology (MT) for Segment Routing based Network Resource Partition (NRP)" - draft-ietf-lsr-isis-sr-vtn-mt-06
>>   Given that the documents that provide the basic definitions needed for this are still active Internet Drafts, it seems premature to last call this document.
>> As a lesser matter, it seems odd that draft-ietf-teas-ietf-network-slices, which defines the terms needed to understand this draft, is an Informative reference.
>> Yours,
>> Joel
>> PS: I considered not writing this email, as it seems quite reasonable to use MT to support what I expect NRPs to be.  So in principle I think the document is a good idea.
>> On 1/10/2024 6:12 PM, Acee Lindem wrote:
>> Note that we are last calling this informational document relating to IS-IS deployment of NRPs using multi-topology. If you have comments, please send them to the LSR list.
>>   Thanks,
>> Acee
>>
>>
>>
>> Begin forwarded message:
>>   From: Acee Lindem <[e-mail]>
>> Subject: Working Group Last Call for "Applicability of IS-IS Multi-Topology (MT) for Segment Routing based Network Resource Partition (NRP)" - draft-ietf-lsr-isis-sr-vtn-mt-06
>> Date: January 8, 2024 at 5:50:21 PM EST
>> To: Lsr <[e-mail]>
>>   This begins a two week LSR Working Group last call for the “Applicability of IS-IS Multi-Topology (MT) for Segment Routing based Network Resource Partition (NRP)”. Please express your support or objection prior to Tuesday, January 23rd, 2024.
>>
>> Thanks,
>> Acee
>>   
>>
>>
>> _______________________________________________
>> Teas mailing list
>> [e-mail]
>> https://www.ietf.org/mailman/listinfo/teas