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Re: LFAs and ECMP

Subject: Re: LFAs and ECMP
From: Alia Atlas
Date: Mon, 14 Feb 2005 15:21:37 -0500
At 12:15 PM 2/14/2005, mike shand wrote:
So describe the above example as a case of how ECMP doesn't guarantee protection - and then up to the implementation/operator to decide what the preference between protection type and cost is?
Don't we already have to discuss the same sort of issues with respect to
LFAs? ie. you may be able to get a viable LFA where you couldn't otherwise
by relaxing the protection type.
We do. The draft describes the selection of an alternate for each primary
next-hop, so it's really part of that... I can just add in an advisory bit
with the example.
But if it were a choice between using an ECMP which may not actually protect against the failure, and using an LFA which is guaranteed to protect against any failure, then I think I would probably choose the latter. It is only in cases where there was no "perfect" LFA that I might be tempted to use a less than unconditionally OK ECMP (or even LFA).
Right. The draft says one should pick an alternate that gives the best
protection possible.
But as you say, to some extent it is an operator/implementation choice.
So I'll clarify a bit with the example - and leave it as the should.


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