Addressing IPv6 Hosts

Throughout this section there have been clues as to how hosts, and specifically interfaces, obtain their IPv6 addresses. The three methods by which an IPv6 host can obtain an IP address include stateless autoconfiguration, statefulautoconfiguration, or manually.
Stateless autoconfiguration is the easiest IPv6 address allocation method available. When used, stateless autoconfiguration uses the network prefix information contained in router advertisements as the first 64 bits of its addresses, and then appends its MAC address in EUI-64 format as the interface portion. This method is especially useful in environment where a DHCP server is neither configured nor present. On local networks without a router, a host using stateless autoconfiguration will use the link local network prefix and append to this its EUI-64 format MAC address.

For a higher degree on control over which addresses IPv6 interfaces use, statefulautoconfiguration can use another addressing method. When an IPv6 node sends out its router solicitation message at startup, the router can be configured to include whether a DHCP server should be used in its reply. If a DHCP server should be used, the node will used attempt to find a DHCP server through the use of multicasts. This is again an improvement over IPv4, where clients attempting to lease an IP address from a DHCP server use broadcast messages.

Finally, IPv6 addresses can also be configured manually. While generally not suggested for individual hosts, certain network nodes (such as routers) will require explicit configuration. Given the length and complexity of IPv6 addresses, it is generally best to use either stateful or stateless autoconfiguration for hosts to reduce potential errors and keep things simple.

Note: You may be curious about how DNS works in an IPv6 environment. Not surprisingly, the method is very similar to DNS in IPv4. However, when a host is attempting to obtain the IPv6 address associated with a fully qualified domain name (FQDN) or hostname, it sends a DNS query looking for the AAAA record associated with the host, rather than the standard A record used to resolve IPv4 addresses.

Author: Dan DiNicolo

Dan DiNicolo is a freelance author, consultant, trainer, and the managing editor of 2000Trainers.com. He is the author of the CCNA Study Guide found on this site, as well as many books including the PC Magazine titles Windows XP Security Solutions and Windows Vista Security Solutions. Click here to contact Dan.