Hi Yakov,

Thanks to point this important subject.

Consider the case where you have a link failure, it is easy for our customers 
to understand that their traffic have been impacted because the traffic was 
crossing the link that has failed.
Now, if to protect this link, we enable FRR and FRR path uses an "uncontrolled" 
path. When the link fails, traffic is switched to FRR path and may use some 
paths that is not well sized to handle this traffic.
This may create congestion on some links. Congestion will affect traffic that 
is not directly concerned by the failure, so customer will loss some traffic. 
For sure, the congestion duration will be bound to the convergence time 
(~seconds), but for some critical applications (that are not essential 
requiring LLQ -> so QoS may not fully help in this, in customer data class is 
congestionned), this is not acceptable. And customers cannot understand that 
they are impacted by an issue in another region of the world. (It's like the 
well known "Butterfly effect" :) )
This problematic is quite similar to the microloop one. Microloops are 
impacting traffic which is not directly concerned by the failure. And globally 
we already had complains for both issues (FRR using bad path and microloops).

Hope it helps to understand our concern.

Best Regards,

Stephane

-----Original Message-----
From: Yakov Rekhter [mailto:[email protected]] 
Sent: Wednesday, December 03, 2014 15:25
To: LITKOWSKI Stephane SCE/IBNF
Cc: Uma Chunduri; Alia Atlas; Loa Andersson; [email protected]; 
[email protected]; [email protected]; 
[email protected]
Subject: Re: [mpls] maturity of the MRT technology 

Stephane,

On 23/11/2014 08:47, [email protected] wrote:
 
> Hi Uma,
>
> >Is this because of domain wide deployment requirements MRT brings-in
> (as elaborated by Stewart?) or you are ok with LFA/rLFA coverage in 
> the network?
>
> No, domain-wide deployment is not an issue. The issue I see in MRT 
> (for my use case) is unoptimality of the FRR path (at least using 
> lowpoint algorithm). But anyway, as I mentioned, I'm not opposed to 
> make MRT progressing at all. It's good to have multiple tools.

While MRT may result in "unoptimality of the FRR path", why this unoptimality 
really matters that much, given that FRR suppose to be used for only a short 
period of time until IGP convergence?

Yakov.

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