| IPv6 address | Leading bits | IPv4 example | Description |
|---|---|---|---|
| ::/128 | 0000....0000/128 (128 bits of zeroes) | Unspecified address | |
| ::1/128 | 0000...0001/128 (all zeroes except very last bit) | 127.0.0.1 | Loopback address |
| FF00::/8 | 1111 1111000... (8 leading zeroes) | 224.0.0.0 through 239.255.255.255 | Multicast address |
| FE80::/10 | 1111 1110 10... | Link local unicast | |
| FEC0::/10 | 1111 1110 11... | 10.0.0.0/8 | Site local unicast (deprecated by IETF) |
| Everything else | Global unicast |
The Link Local Unicast is an address that is not permitted to "leak" off of the local network segement. The Site Local Unicast is similarly not permitted to leak out of an enterprise network (similar to RFC 1918 addresses). Note, however, that the Site Local Unicast definition is no longer considered part of the IPv6 addressing standard.
In addition, there are standard methods for encapsulating IPv4 addresses inside of IPv6 addresses. The so-called "IPv4-Compatible Address" follows the convention of just putting the IPv4 address into the last 32 bits of the 128-bit IPv6 address and padding all of the higher order bits with zeroes. For example, the address 192.168.11.1 would be written as 0:0:0:0:0:0:C0A8:0B01 or ::C0A8:B01, or following another convenient standard for representing IPv6 address that contain IPv4 address, ::192.168.11.1. Once again, this method is also deprecated because it doesn't match well with newer methods for interoperating IPv4 and IPv6 networks. However, you will sometimes see it in use in older IPv6 implementations.
Another common method for writing IPv4 addresses inside of IPv6 addresses is called "IPv4-Mapped Addressing", and it follows a similar strategy. Once again, the last 32 bits encapsulate the IPv4 address, but in this method, the IPv4 address is padded by 16 binary ones and 80 zeroes. So this time the address 192.168.11.1 becomes 0:0:0:0:0:FFFF:C0A8:0B01, or ::FFFF:C0A8:B01.
Finally, some Cisco documentation talks about so-called Site-Local addressing, which has a binary prefix of 1111 1110 11, or FEC0::/10 in hex. The Site-Local addressing concept has now been deprecated and removed from the IPv6 standard. While individual sites are free to continue using this addressing scheme and manually block these addresses from leaking out of a particular administrative area by means of access-lists, these addresses are now considered to be standard unicast addresses.