摘要：The current Internet Protocol, known as IPv4 (for version 4), has served the Internet well for over 20 years, but is reaching the limits of its design. It is difficult to configure, it is running out of addressing space, and it provides no features for site renumbering to allow for an easy change of Internet Service Provider (ISP), among other limitations. Various mechanisms have been developed to alleviate these problems (for example, Dynamic Host Configuration Protocol [DHCP] and Network Address Translation [NAT]), but each has its own set of limitations.
