Eduardo,
John G. Scudder wrote:
Eduardo,
Remember that the input to the aggregation step is the Local RIB.
Prefixes to be aggregated need to share the same next hop (not in the
BGP NEXT_HOP sense necessarily, but in the actual
what-you-put-in-the-forwarding plane sense). The AS_PATH is irrelevant
to the aggregation step. This is because the aggregation is never
exposed outside the local router. Indeed, modulo the "creating
additional routable space" issues introduced by "Type 4" of the draft it
should be impossible for an outside observer to even tell if FIB
aggregation is in use or not.
The whole thing is orthogonal to what goes on in the control plane.
As for the evaluation methodology, Lixia or one of her co-authors will
have to address that.
As far as I understood, they considered the first AS number on each path is its
"nexthop" attribute, because they don't have the actual nexthops in the data.
That's why they had to validate this approach by showing that a given router,
usually uses the same nexthop for almost all the prefixes that it reaches
through a given neighboring AS.
This might come from the fact that it always has the same IGP tie-break winner
when comparing multiple nexthops of the same neighboring AS. And most of the
time when comparing paths from the same neighboring AS you reach that BGP DP rule.
However you can find designs were having multiple nexthops at same IGP distance
from a given PE holds true for almost every (PE,neighboring AS). The plot on
such networks could have been much less favorable for the validation of the
approach I guess.
Regards,
Pierre.
--John
On Nov 11, 2009, at 2:26 PM, Eduardo Ascenço Reis wrote:
Hi,
Regarding FIB Aggregation draft (draft-zhang-fibaggregation-02.txt),
prefixes that would be aggregated share the same NEXT_HOP and AS_PATH
attributes.
Is that correct?
From Lixia presentation I got that the evaluation methodology
extracted NEXT_HOP from AS_PATH information (Route Views Archive
Base).
Thanks,
--
Eduardo Ascenço Reis
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