As we all know the IPv4 address for localhost is 127.0.0.1 (loopback address). What is the IPv6 address for localhost and for 0.0.0.0 as I need to block some ad hosts.
As we all now that IPv4 address for
localhostis127.0.0.1(loopback address).
Actually, any IPv4 address in 127.0.0.0/8 is a loopback address.
In IPv6, the direct analog of the loopback range is ::1/128. So ::1 is the one and only IPv6 loopback address.
And while the hostname localhost will normally resolve to 127.0.0.1 or ::1, I have seen cases where someone has bound it to an IP address that is not a loopback address. This is a bit crazy ... but sometimes people do it.
Blocking 0.0.0.0 makes no sense. In IPv4 it is never routed. The equivalent in IPv6 is the ::/128 address ... which is also never routed.
The 0.0.0.0 and ::/128 addresses are reserved to mean "any address". So, for example a program that is providing a web service may bind to 0.0.0.0 port 80 to accept HTTP connections via any of the host's IPv4 addresses.
For more information, read the Wikipedia pages on IPv4 & IPv6 addresses:
For a URL use http://[::1]:80/ or http://[::1]/
The ipv6 localhost is ::1. The unspecified address is ::. This is defined in RFC 4291 section 2.5.
For use in a /etc/hosts file as a simple ad blocking technique to cause a domain to fail to resolve, the 0.0.0.0 address has been widely used because it causes the request to immediately fail without even trying, because it's not a valid or routable address. This is in comparison to using 127.0.0.1 in that place, where it will at least check to see if your own computer is listening on the requested port 80 before failing with 'connection refused.' Either of those addresses being used in the hosts file for the domain will stop any requests from being attempted over the actual network, but 0.0.0.0 has gained favor because it's more 'optimal' for the above reason. "127" IPs will attempt to hit your own computer, and any other IP will cause a request to be sent to the router to try to route it, but for 0.0.0.0 there's nowhere to even send a request to.
All that being said, having any IP listed in your hosts file for the domain to be blocked is sufficient, and you wouldn't need or want to also put an ipv6 address in your hosts file unless -- possibly -- you don't have ipv4 enabled at all. I'd be really surprised if that was the case, though. And still though, I think having the host appear in /etc/hosts with a bad ipv4 address when you don't have ipv4 enabled would still give you the result you are looking for which is for it to fail, instead of looking up the real DNS of say, adserver-example.com and getting back either a v4 or v6 IP.
Just for the sake of completeness: there are IPv4-mapped IPv6 addresses, where you can embed an IPv4 address in an IPv6 address (may not be supported by every IPv6 equipment).
Example: I run a server on my machine, which can be accessed via http://127.0.0.1:19983/solr. If I access it via an IPv4-mapped IPv6 address then I access it via http://[::ffff:127.0.0.1]:19983/solr (which will be converted to http://[::ffff:7f00:1]:19983/solr)
来源：https://stackoverflow.com/questions/40189084/what-is-ipv6-for-localhost-and-0-0-0-0