IPv4 BGP Table Reduction Analysis - Prefixes Filter by RIRs Minimum Allocations Boundaries

Andy Davidson andy at nosignal.org
Sun Dec 2 14:59:19 UTC 2007


On 29 Nov 2007, at 22:05, Eduardo Ascenco Reis wrote:

> Although the BGP data is around one month old and the original  
> focus was on Brazilian AS and IP prefixes, the general analysis  
> covers all Regional Internet Registries (RIRs).
[...]
> The methodology shows a good efficiency (around 40%) reducing BGP  
> table size, but the estimated number of affect prefixes are also  
> high (around 30%).

This is an interesting piece of work, and highlights an interesting  
model (40% table size saving hurts 30% of traffic.)

I have a couple of thoughts:

from the text:
> Although representing less than 1% of all suboptimal and  
> unreachable prefixes, /20 prefixes call attention because of their  
> mask size to be expected as normal. In this experiment all /20  
> affected prefixes are from 2 RIPE CIDR (62/8 and 212/7) with /19  
> longest prefix, which data could eventually be used by RIPE to  
> reviews these CIDR policy allocations. This is only one use example  
> of applications that can be derived from analysis like this one.

Do you still have the lab setup ?  Could you work out what happens to  
the routing table and traffic routing if you permit one deaggregation  
per rir prefix ?  I.e. This /19 is permitted to become two /20s, but  
it is not permitted to become four /21.  My desire would be to see  
the resolved routing table look almost as trim as your 40% saving,  
but a significant amount of traffic routed as intended by the  
originating network.

Lastly, perhaps another comment for your recommendations and  
conclusions section could be that traffic is hurt most in this model  
for networks who deaggregate most.  Lets encourage people who read  
this document to infer that aggregating their prefixes would improve  
their reach in the post 250k routing table world.

Andy




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