IPv6 Essentials

Network Designs

When we start using IPv6, different approaches are possible. I’ll give some sample scenarios here. It is important to understand that getting started with IPv6 does not mean you have to tear down your IPv4 infrastructure or switch everything at one time. The specific mechanisms for coexistence of IPv4 and IPv6, such as 6to4 operations, tunneling, and protocol translation, are explained in Chapter 10.

The simplest way to start using IPv6 is to implement single IPv6 hosts in an IPv4 network. They will autoconfigure for a link-local IPv6 address and be able to communicate with one another over IPv6. They use ICMPv6 neighbor discovery messages to locate one another. If they also have an IPv4 stack, they can communicate with the IPv4 world. Using ISATAP, a large number of hosts within a site with no IPv6 router can communicate. If one of the IPv6 nodes is configured as a 6to4 gateway and is connected to the Internet, other IPv6 sites on the Internet can be reached through the use of a 6to4 relay router.

The next expansion step is to add an IPv6 router to the scenario. As discussed in Chapter 4, router discovery and Router Advertisement messages can be used for configuration of IPv6 hosts on the subnet. For instance, the router can be configured to advertise a subnet prefix and hop limit. Thus, all IPv6 hosts on the subnet can be configured for their address without the need for static configuration or even a DHCP server. This is all done by the autoconfiguration mechanisms, ...