IPv6 prefixes explained

IPv6 addresses are hard to read. Prefixes are also new for us. In this article I will show common prefixes and how to use them.

IPv6 addresses

There are many ways to express an IPv6 address. For example, the addresses below are all valid and equivalent:

2001:0db8:0000:0000:0000:0000:1428:57ab
2001:0db8:0000:0000:0000::1428:57ab
2001:0db8:0:0:0:0:1428:57ab
2001:0db8:0:0::1428:57ab
2001:0db8::1428:57ab
2001:db8::1428:57ab

The important lesson here is that the IPv6 addresses are complex and long. One or any number of consecutive groups of 0 value may be replaced with two colons (::).

Prefixes

You can specify a prefix on an IP address. Prefixes have the syntax /#bits, like 2001:db8::/32. Prefixes are only used for routing as networks that connect computers are expected to have a /64 prefix.

Each group of octets in an IP address represents 16 bits, giving us a total of 8 groups. A mask of /32 is thus the two first groups.

IP	2001	:	0db8	:	0000	:	0000	:	0000	:	0000	:	1428	:	57ab
Prefix	/16		/32		/48		/64		/80		/96		/112		/128

Sources

Wikipedia is used as the main source. Their article on IPv6 is used as the source.