IPv6 also implements many other new features. It simplifies aspects of address assignment ([[#Stateless address autoconfiguration|stateless address autoconfiguration]]) and network renumbering ([[#prefix and router announcements|prefix and router announcements]]) when changing Internet connectivity providers. The IPv6 [[subnetwork|subnet]] size has been standardized by fixing the size of the host identifier portion of an address to 64 bits to facilitate an automatic mechanism for forming the host identifier from [[Link Layer]] media addressing information ([[MAC address]]). [[Network security]] is also integrated into the design of the IPv6 architecture, and the IPv6 specification mandates support for [[IPsec]] as a fundamental interoperability requirement.
For deployment, IPv6 is largely incompatible with IPv4 at the packet level, and translation services dohave notdeficiencies seemthat practicalmake them controversial. <ref name=4966>RFC 4966 Reasons to Move the Network Address Translator - Protocol Translator (NAT-PT) to Historic Status</ref> IPv6 and IPv4 are therefore treated as almost entirely separate networks with devices having two separate protocol stacks if they need to access both networks, with tunneling of IPv6 on IPv4 and vice versa. In December 2008, despite marking its 10th anniversary as a Standards Track protocol, IPv6 was only in its infancy in terms of general worldwide [[IPv6 deployment|deployment]]. A 2008 study<ref>[http://www.ripe.net/ripe/meetings/ripe-57/presentations/Colitti-Global_IPv6_statistics_-_Measuring_the_current_state_of_IPv6_for_ordinary_users_.7gzD.pdf ''Global IPv6 Statistics - Measuring the current state of IPv6 for ordinary users'', S. H. Gunderson (Google), RIPE 57 (Dubai, Oct 2008)]</ref> by [[Google Inc.]] indicated that penetration was still less than one percent of Internet-enabled hosts in any country. IPv6 has been implemented on all major operating systems in use in commercial, business, and home consumer environments.<ref>[http://arstechnica.com/news.ars/post/20081113-google-more-macs-mean-higher-ipv6-usage-in-us.html Google: more Macs mean higher IPv6 usage in US]</ref>
