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Re: node disjoint and SRLG (was: questions on draft-bryant-ipfrr-tunnels

Subject: Re: node disjoint and SRLG was: questions on draft-bryant-ipfrr-tunnels-01.txt
From: Alia Atlas
Date: Tue, 23 Nov 2004 10:58:33 -0500

The percentage that is missing is then those that require a single primary tunnel for repair? These are the number for repair for node failure? I'm trying to get a sense of what the benefit from LFA is versus the tunnels versus the DF versus the secondary, etc. I'm interested in the different benefits for link protection and for node protection.
In a somewhat related question, I understand that you are using a
next-next-hop to proxy for destinations. Is it possible that you miss a
viable LFA to a destination because of this? I.e., the neighbor may be LFA
with respect to the destination but not the next-next-hop?
Also, how do you handle the ECMP cases where you may have multiple
next-next-hops (even from the same next-hop)? That seems like a
per-destination decision.

At 04:40 AM 11/23/2004, mike shand wrote:
Alia, these may not be in the form you would like (but since I have them to hand....).
These are the same networks as before. df% is the percentage of repairs
which required directed forwarding (the same as before, the fraction of
individual repairs which needed DF). LFA% is the percentage which simply
used LFA (i.e. no tunnels)
Note that is no tunnels for ALL traffic. This doesn't mean that this is
the percentage of traffic which would not be tunnelled. That would be much
higher, since we can easily do per destination LFA determination.
In case that is not clear, let me elaborate for the simple link failure
case. We can compute a repair for the failure of SE. Sometimes we can
repair ALL traffic (even that with a destination of E) by using LFA. Other
times we will need a tunnel to get to E. However, in that case, we can
compute the set of destinations which have LFAs, and we would only use the
tunnel for the remaining traffic. Of course it would theoretically be
possible to compute different tunnels for different destinations, but that
is not computational feasible.

sec %   df%     LFA%
0.79%   4.6%    69.4%
13.77%  41.9%   45.5%
3.98%   19.1%   66.3%
1.47%   1.2%    59.3%
0.50%   1.3%    79.4%
4.64%   1.3%    61.9%
0.00%   0.0%    62.6%

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