What is the IPv6 equivalent of 192.168.xxx.xxx? [duplicate]

I have a server which responds differently to requests from the general internet as opposed to the intranet. For IPv4 I can simply check if the address begins with 192.168. This works for my needs. What is the equivalent for IPv6?

First of all "intranet" is not limited to 192.168. There are 3 private networks defined in RFC-1918: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16.

In IPv6, it is called a Unique local address: http://en.wikipedia.org/wiki/Unique_local_address and covered in RFC-4193 -- all addresses matching FC00::/7. Basically, you should be able to search for IPv6 addresses starting with fc or fd.