While I was reading through this documentation I found this :
Code:
http://www.tdoi.org/mirrors/bieringer/Linux+IPv6-HOWTO/x530.html
3.2.3.3. Assigned by provider for hierarchical routing
These addresses are delegated to Internet service providers (ISP) and begin with
2001:

Is this (2001) special case for the link above ? or it is for all IPv6 addresses ?