IPv6 prefixes

The IPv6 prefix concept is similar to IPv4 subnetting. An IPv6 address with a prefix is written as an IPv6 address followed by a decimal number representing the number of bits in the address that constitute the prefix. It is written as:

ipv6-address/prefix-length

where:

ipv6-address: is an IPv6 address in any notation
prefix-length: is a decimal value specifying how many of the leftmost contiguous bits of the address comprise the prefix.

For example, the following are legal representations of the 60-bit prefix 12AB00000000CD3 (hexadecimal):

12AB:0000:0000:CD30:0000:0000:0000:0000/60
12AB::CD30:0:0:0:0/60
12AB:0:0:CD30::/60

When writing both a node address and a prefix of that node address (for example, the node subnet prefix), the two can be combined as follows:

The node address

12AB:0:0:CD30:123:4567:89AB:CDEF

and its subnet number

12AB:0:0:CD30::/60

can be abbreviated as

12AB:0:0:CD30:123:4567:89AB:CDEF/60