bill001g :
You can buy a whole book on how subnetting works there is no simple answer other than to go study it. There are many many free resources on the internet.
I have heard IPv6 was going to replace everything for the last 15yrs and it still has not happened. To get IPv6 from a ISP you need to pay extra in most cases and there are only a small number of commercial sites that use it. The only place it is really used is in china and other similar places that were very late to adopt internet and got shut out of the ip pools. You will see real ipv6 address on mobile phones but they also have private ipv4 addresses that are natted and used for the vast majority of the applications.
Hard to say so far everyone has done a very good job of getting around the shortage of ip addresses.
I just got my HE IPv6 Tunnel setup
ping www.google.com
Pinging www.google.com [2607:f8b0:4009:805::1014] with 32 bytes of data:
Reply from 2607:f8b0:4009:805::1014: time=19ms
Reply from 2607:f8b0:4009:805::1014: time=17ms
Reply from 2607:f8b0:4009:805::1014: time=17ms
Reply from 2607:f8b0:4009:805::1014: time=17ms
Ping statistics for 2607:f8b0:4009:805::1014:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 17ms, Maximum = 19ms, Average = 17ms
nslookup
Default Server: pfsense.localdomain
Address: 192.168.1.1
> www.google.com
Server: pfsense.localdomain
Address: 192.168.1.1
Non-authoritative answer:
Name: www.google.com
Addresses: 2607:f8b0:4009:805::1014
173.194.46.84
173.194.46.81
173.194.46.83
173.194.46.82
173.194.46.80
> quit
ping 173.194.46.84
Pinging 173.194.46.84 with 32 bytes of data:
Reply from 173.194.46.84: bytes=32 time=13ms TTL=54
Reply from 173.194.46.84: bytes=32 time=12ms TTL=54
Reply from 173.194.46.84: bytes=32 time=13ms TTL=54
Reply from 173.194.46.84: bytes=32 time=12ms TTL=54
Ping statistics for 173.194.46.84:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 12ms, Maximum = 13ms, Average = 12ms
As you can see, the latency is about 40% higher! Good news is I can still speedtest 46/46 on my 50/50 connection, and it does show up as IPv6 traffic, but only for IPv6 enabled speed sites.
We are only just now reaching the real shortage of IPs. We're down to our last /8 in the USA. The rest of the world grew up with few IPs, but now the USA is about to get hit with reality.
It's not going to be a brick wall by any means, but prices and issues will start to crop up. For companies not grandfathered in from the beginning of the Internet, you only lease IP addresses. If you can't show a good reason every year for you to keep your IPs, they can take them back.
This may cause some companies to have to restructure some of their public facing networks because they may lose their IPs that they've had for years.