North American Network Operators Group

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BGP filtering of supernets out of classful space

  • From: Jeff Haas
  • Date: Fri May 19 11:50:47 2000

In attempting to help someone with regards to BGP announcement 
filtering from the IRR we've found the following situation:

A provider in China has been assigned addresses in the
traditional class C space.  APNIC's assignment is a /16 for this allocation.
Said provider, trying to be good Internet citizens are announcing
only aggregates of /16.

However, they're running into several providers that are filtering
the announcements because they aren't /24.  Experimentation has
proven that announcing /24's will solve this problem.  This obviously
clutters up the global routing tables.

The primary justification I can see for such filtering is to prevent
"sink routing" - or catching everything else where more specific routes
don't exist.  (This would probably be a Bad Thing for the provider
foolishly making such announcements - a very effective self DoS attack.)

What methodology are providers using for these types of route
filtering issues now?

(I'll save the IRR pulpit for later.)

And yes, I have directed the provider having the routing issues to
contact each ISP doing the filtering separately.

Jeffrey Haas - Merit RSng project - [email protected]