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That's why filtering /20 only without re-aligning the holes in the block won't work. In the end /20 make the routing table looks pretty but they are black-holing lots of traffic.

Well, it won't. The proposal for filtering is to filter on assigment boundary, and for swamp space filter on /24. Now, what will break is people punching holes in their PA space for multihomed users. Funny enough, this has never been discussed (to my knowledge) as a problem in PTOMAIN WG of the IETF. There the argument was for traffic engineering and commercial relationships...

Even for PI and swamp space, if the organization divides their space among different ISPs for multi-homed links. You still got a problem.

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As we all agree that re-assign address is NOT practical at all thus just filtering /20 block is not a good solution.

That is not the suggestion. See above. The assignments per block and RIR is well known.

Well known and lots of holes in it. That's the problem. Ping Lu Cable & Wireless USA Network Tools and Analysis Group W: +1-703-292-2359 E: plu@cw.net