Quiz Entry - updated: 2026.07.14
What do the special addresses ::/128 and ::1/128 mean?
:: (all zeros) is the "unspecified" address meaning "I have no address yet"; ::1 is the loopback — IPv6's equivalent of IPv4's 127.0.0.1.
| Address | Name | Meaning |
|---|---|---|
::/128 (128 zero bits) |
Unspecified | Indicates the absence of an address — used as a source while a host is still configuring itself |
::1/128 (127 zeros + one 1) |
Loopback | Refers to the host itself ("localhost") |
The unspecified address is what a host puts in the source field during Duplicate Address Detection, before it owns a valid address. You can never route to :: — it only ever appears as a placeholder source.
Tip: ::1 is to IPv6 what 127.0.0.1 is to IPv4 — type ping ::1 to test the local stack.