It's a couple of years old now, but RIPE have quite a good article on the visibility of various lengths of IPv4 and IPv6 prefixes at the time:
https://labs.ripe.net/Members/dbayer/visibility-of-prefix-lengths Edward Dore Freethought Internet ----- Original Message ----- From: "Paul Mansfield" <[email protected]> To: [email protected] Sent: Wednesday, 17 April, 2013 11:18:14 AM Subject: Re: [uknof] First one of these I've received... what's considered to be the smallest v4 block which would be globally routable given BGP prefix filtering?
