Cisco IOS Cookbook, 2nd Edition

Introduction

IPv6 was initially developed to resolve a critical problem with the existing Internet Protocol (commonly called IPv4). An IPv4 address has 4 octets, or 32 bits, to identify every device on the Internet. If each node has a single unique address, then there can be at most 4,294,967,296 (that is, 2^32) devices on the Internet. And that doesn’t account for the fact that most routers and many servers have several addresses.

And, in fact, the situation is worse than that because of how IP addresses were originally allocated. With a handful of large organizations using Class A and B addresses, and large blocks of the IPv4 address range set aside for things like multicasting, the Internet Assigned Number Authority (IANA) was quickly running out of addresses. The Internet Engineering Task Force (IETF) went off to create a new version of the IP protocol with larger addresses to fix this problem.

Many options were considered, and in the end they came up with IPv6. Of course, in the meantime, because the available assignable address ranges were rapidly running out, a few simple interim standards such as NAT and CIDR were drafted that effectively saved IPv4 for many years to come.

Today the case for IPv6 is somewhat different. The force driving the new protocol is still based on increasing the number of addresses, but it is now a local rather than a global problem. Several large telephone companies, particularly in Asia, have started to encounter problems in assigning an IP address ...