Why should I get IP addresses from my ISP rather than from the RIPE NCC?
The RIPE NCC cannot guarantee that any address space that it allocates can be globally routable. This is because filtering policies that bigger network providers use around the world are beyond our control.
The best way to avoid filtering problems is to make sure that your network is numbered into the address range of a larger network (such as that of your upstream ISP), so that many addresses can be aggregated and announced globally as a single route. Because a global route has a shorter prefix, it will increase its chances of being unaffected by the filtering policies of large transit providers.
It is in the interests of the Internet community as a whole that the number of separate routes in the global routing tables be kept to a minimum. This is why we encourage organisations to obtain address space from upstream ISPs wherever possible.