Re: [Lsr] draft-lin-lsr-flex-algo-metric-00

Hi Mengxiao,

please see inline:

On 25/03/2022 07:35, Chenmengxiao wrote:
> Hi Peter,
> 
> Thank you for the comments.
> 
> Time for the presentation is very limited. Glad to receive your comments 
> here.
> 
> I agree that flex-algo is much easier to deploy and manage than MT, 
> which make it a popular tool now.
> 
> But I think using algorithm-specific link metric will not cause the loss 
> of this property.
> 
> For example, flex-algo 128 and flex-algo 129 need to use different 
> metrics of the same metric-type for the same link.
> 
> Solution A: Use algorithm-based metric for algorithm 128 and algorithm 129
> 
> Solution B: Use metric-type-based metric for metric-type 128 and 
> metric-type 129 (according to Shraddha's suggestion, 
> draft-ietf-lsr-flex-algo-bw-con)
> 
> Both in the two solutions, extra link metric tlvs need to be advertised, 
> and they are stored locally, no matter algorithm-based or metric-type-based.

yes, but for B, any other algorithm may share the metric used for algo 
128 or 129. That is not possible with A.

You may argue that in your case you only have two algos, so the result 
ts similar. Yes, but from the architecture perspective there is a 
difference. Not to mention that for A we would need to extend the FAD.

> 
> During path computation, the difference is that, solution A needs to 
> check if there is algorithm-based metric for the link. If yes, 
> algorithm-based metric is preferred. If no, common metric is used.
> 
> IMHO, even if the algorithm-specific link metric is used, flex-algo is 
> still light weight, compared with MT.

not really, because it advertise algo specific metric that can not be 
used by any other algo, which is similar to topology specific metric in MT.

I would encourage you to consider option B as a solution for your problem.

thanks,
Peter

> 
> Thanks,
> 
> Mengxiao Chen
> 
> -----Original Message-----
> From: Lsr [mailto:lsr-bounces@ietf.org] On Behalf Of Peter Psenak
> Sent: Thursday, March 24, 2022 11:09 PM
> To: lsr@ietf.org
> Subject: [Lsr] draft-lin-lsr-flex-algo-metric-00
> 
> Hi,
> 
> as I was unable to make my comments during the presentation, let me put
> 
> them here:
> 
> When we started with the flex-algo work, there has been a lengthy
> 
> discussion on why not to use the multi-topology (MT) instead. We always
> 
> wanted flex-algo to be light weight and as a result easy to deploy and
> 
> manage. I believe that was one of the reasons why flex-algo has been
> 
> successfully deployed. We do not want to loose that very property of the
> 
> flex-algo architecture.
> 
> What you are proposing is what MT was invented for and we do not want
> 
> flex-algo to become a new version of MT.
> 
> You have two ways to solve your problem:
> 
> a) use MT
> 
> b) if you want to solve your problem with flex-algo, please use what
> 
> already exists in flex-algo. Please look at
> 
> draft-ietf-lsr-flex-algo-bw-con as others have pointed out.
> 
> thanks,
> 
> Peter
> 
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