The loopback IP address in IPv6 format is: 0000:0000: 0000:0000: 0000:0000: 0000:0001
which is shortened to: 0:0: 0:0: 0:0: 0:1
which is then shortened to (keep last 2 words, ie. 4 bytes, to match IPv4): :0:1 (But I still don't know why it's double colons instead of single colon before 1, maybe for implying that there are 4 bytes here)
and simplified as: ::1
Expand ::1 into IPv4 format, it is: 0.0.0.1
But this is not the same as 127.0.0.1, where's the number 127?