We are running out of IP addresses in IPv4 and all other countries than the US is pushing IPv6. The major test of IPv6 infrastructure will be carried out this summer when all major ISP's will be using IPv6 for 24 hours.

This brings up the question of what  the equivalent of a C-class is in IPv6 in terms of SEO.

The IPv6 range has so many addresses that ISP's could hand out addresses for every pixel on your website. Many hosting companies in Europe are ready to assign IPv6 addresses so what would you ask for in order to get the C-class effect?

Personally I have no idea.

Someone please correct me if I'm wrong, as this really isn't my area.


However, as I understand it, the whole classful notation in IPv4 died out in the 90s, and was replaced by CIDR. In IPv4 CIDR, a /32 is a single IP address, and a /24 is an 8 bit block of IP addresses; in other words 256, the same as a class C in classful notation. As such:

Class C = /24

Both mean a 256 (in reality 254) host subnet, e.g., the 256 IPs between, let's say, 192.168.1.0 and 192.168.1.255

With IPv6, I believe a subnet is a /64, but we're talking 18,446,744,073,709,551,616 IP addresses instead of 256, so they're not really comparable.

Even more staggering is that with IPv4, the standard allocation size was a /24 (256 IP addresses), and in Europe at least, apparently IPv6 /48s are standard, which is 1,208,925,819,614,629,174,706,176 IPs.

So will Google think that sites on the same IPv6 /48 or /64 may be related? I'm with Torben. No idea! I'm certainly not going to lose any sleep over it.

>will Google think

Probably easiest for them to see 'who owns the block'

fwiw along the lines of backlink class C diversity, ive noticed google will temporarily block scraping their serps if the activity occurs too frequently across the same class C (IPs involved were all with the same host though).