Q: Ip6tables prefix subnet I have a rule in iptables v4 that block prerouting from this IP: 224.0.0.0/3
What is IP6 address equivalent?
I used this website
http://www.gestioip.net/cgi-bin/subnet_calculator.cgi
It says "6to4 prefix": 2002:e000:0000::/48 - Is this 224.0.0.0/3 equivalent?

A: Stop thinking that each IPv4 address has a 1:1 equivalent IPv6 address. You should be asking about the purpose of the firewall rule (and about whether that purpose is applicable to IPv6 in the first place), not about literal translation.

224.0.0.0/3 has a specific meaning – it is the IPv4 Multicast address space. Its equivalent, the IPv6 Multicast address space, would be ff00::/8.
However, keep in mind that certain types of multicast are required for IPv6, so you should be very careful about what to block. Specifically, various IPv6 features use link-local scope multicast in the ff02::/16 prefix and you should never block this /16 for input/output.
(Though, link-local means that it will never be routed so it's safe to block it for forwarding.)
It's also safe to block other multicast scopes, so as long as you allow ff02::/16, you probably can safely block the rest of ff00::/8.

It says "6to4 prefix": 2002:e000:0000::/48 - Is this 224.0.0.0/3 equivalent?

No.
6to4 is a tunnel service, not a direct 1:1 translation – it's only built in such a way that the IPv4 host 1.2.3.4 automatically gets the rights to the corresponding 2002:0102:0304::/48 prefix, but beyond that, the two kinds of addresses are absolutely not equivalent.
This also implies that 6to4 mappings are only valid for unicast destinations, not multicast.
