David,
Checking each prefix sounds like an awful lot of work, much better to bitbucket a entire countries prefixes if they collectively don't account for 0.nnn% of your traffic.
Except that prefixes aren't allocated by country. Prefixes are allocated to ISPs (mostly).
I guess i should have used a ;-). My point, If US operators only want to accept prefixes for 'free' from networks that account for a percentage of their traffic, your in a position to effectively blackhole much of the developing nations Internet. Is access to a countries Internet more or less important than access to a route with a different bit length or traffic level ? The size of prefix isn't necessarily the only basis for that prefixes value.
-drc
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