Re: Every user?
@AC on the subject of sharing the external IPv4:
Yes and no. Most ADSL ISPs will give the "outside" of your router its own public IPv4 address - your household will share this address, but your neighbours ill not. They *might* give it an RFC-1918 private address and then have a bunch of such routers hiding behind a (much smaller) group of public addresses that are imposed by NAT on a large router in the guts of the ISP's network. This is known as "Carrier Grade NAT", and introduces its own collection of weirdness, mostly related to how protocols like SIP can allow direct media connections between households that belong to the same CGNAT router. (There are also secondary weirdnesses in that the individual household is no longer able to freely change its internal RFC-1918 numbering plan, and it is in no way apparent which address range(s) he can use, aside from the default one.)