De Wikipedia :
IPv4 network standards reserve the entire 127.0.0.0/8 address block for loopback purposes. That means any packet sent to one of those 16,777,214 addresses (127.0.0.1 through 127.255.255.254) will be looped back. IPv6 has just a single address, ::1.
Portanto, para o IPv6, é apenas ::1
ou ::1/128
.