[c-nsp] vs isis routing levels

[Mark Tinka]

On Sunday, December 22, 2013 02:36:01 PM Adam Vitkovsky 
wrote:

> Anyways even without LFA, on an up to date HW the SPF
> (full/incremental) is in order of microseconds.
> So I'd checkout the spf logs to see how long it takes to
> complete full SFP for 1500 priority 1 prefixes (i.e.
> loopbacks) multiply by 10 to account for the metro
> networks and if that's still acceptable I'd keep it all
> L2. I guess programing the line-cards is still the
> biggest holdup and this is solved by the (r)LFA.

I suppose the issue with fast covergence is not how quickly 
each individual router reacts to the fault, but how long it 
takes the entire network to do so (the sum of the parts).

LFA is helpful because the repair is localized (it's a 
device problem, not a network problem), and immune to the 
time taken/needed to run a full SPF after link failure 
detection, i.e., LFA negates the need to wait for 
convergence, from the point of view of a single device, and 
the network at large.

Mark.
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