R: not rewriting next-hop, pointing default, ...

For ISPs with a lot of direct (i.e., private) peers, on the public
NAP routers you may want to consider not installing the routes from the
private peers. This approach could reduce the damage to your private
links by default-pointing attack. It may also make you less likely
a target due to black-holing of certain traffic.

This approach is not applicable if transit service is provided at
the public NAP.

-- Enke