| > I get a dynamic /64 prefix from my ISP at home, which would be large even if it were assigned to my work office; why is the maximum prefix length /48 for a single site and /32 for 3k sites? The default subnet size for IPv6 is /64, and a single "site" is /48. There are 16 bits between those. Comparing with IPv4, where a 'typical' subnet is /24, if you were given 16 of space to play with as you see fit, you'd be assigned a /8—i.e., an entire Class A. (Which is what most companies use now anyhow—i.e. 10/8—and then have to futz around with NAT.) So a 'typical' IPv6 allocation is as many IP addresses as what some of the largest corporations have. Plus all of those addresses are available for use on the public Internet is you wish: just change your firewall from default-deny to allow certain segments. > Aside from the obvious argument of wastefulness, aren't we just priming the same issue we have with IPv4 now to occur thirty, forty years down the line? No. The numbers involved with IPv6 are literally astronomical: * Stars in the Milky Way: 400 Billion * Galaxies in the universe: 2 Trillion So (4x10^11 )x(2x10^12 )=8x10^23 stars in the universe. * Size of IPv6 address space: 3.4x10^38 Find the ratio between addresses and stars: * 3.4x10^38 / 8x10^23 IPv6 offers about 430 trillion times more addresses than estimated stars in the universe. From Tom Coffee's presentation "An Enterprise IPv6 Address Planning Case-Study" * https://www.youtube.com/watch?v=7Tnh4upTOC4 Another way of looking at it: * math property: x^y = x^(a+b) = (x^a )x(x^b ) * IPv4 addresses are 32 bits (2^32 ) * 2^32 ~ 4.3 billion * So the IPv4 Internet has ~4.3B devices on it * IPv6 subnets are 64 bits, /64 (2^64 ) So, a IPv6 2^64 subnet is the same as (2^32 )x(2^32 ), which means (4.3B)x(IPv4 Internet). I.e., a single IPv6 subnet can hold the equivalent of four billion (IPv4) Internets. A third way: * On the surface of the Earth (land+water), there are 8.4 IPv4 addresses per km^2. Not counting the oceans, that would be 28 IPv4 addresses per km^2 land. * IPv6 gives 10^17 addresses per mm^2 (yes, square millimeter). In terms of volume, 10^8 IPv6 addresses per mm^3 throughout the Earth. * Via: https://news.ycombinator.com/item?id=28326806#unv_28331245 |