One of the things that come up whenever IPv6 is mentioned on certain news sites, is that there are people out there who think that NAT solves all of the address size problems and doesn’t have any negatives. I could present a whole series of blog articles on why NAT is the work of the devil, and presents a clear and present danger to life, liberty, and the pursuit of happiness (I might be exaggerating just a touch here).
The naive approach to a security issue originating from a certain network address is to block that network address permanently, pending an appropriate response, or temporarily. Not a bad idea although it does resemble a game of hunt the wumpus, and to assist in this, there are community based collective blocklists.
But what happens when you block an address, and that address is the public address of a NAT device? You block everyone sharing that public address, which could be just a household or it could be thousands of unconnected people. For instance, I have up to 32,000 people behind a handful of public IP addresses.
And yes I do regularly see problems where blocks have been put in place, and from what I can see this is a problem that is widely shared amongst people who NAT.
And once you are blocked in this way, you may be able to get it removed if you manage to identify which blocklist you are on, stop the network abuse and it has a well-run mechanism for removal. Most blocklists (including the ones I run) don’t work this way.
Every IP address has a reputation associated with it, and if you share a public IP address that has a poor reputation, parts of the Internet will disappear for you, and these include some well known services.