<P> On the Internet, data is transmitted in the form of network packets . IPv6 specifies a new packet format, designed to minimize packet header processing by routers . Because the headers of IPv4 packets and IPv6 packets are significantly different, the two protocols are not interoperable . However, in most respects, IPv6 is an extension of IPv4 . Most transport and application - layer protocols need little or no change to operate over IPv6; exceptions are application protocols that embed Internet - layer addresses, such as File Transfer Protocol (FTP) and Network Time Protocol (NTP), where the new address format may cause conflicts with existing protocol syntax . </P> <P> The main advantage of IPv6 over IPv4 is its larger address space . The length of an IPv6 address is 128 bits, compared with 32 bits in IPv4 . The address space therefore has 2 or approximately 7038340000000000000 ♠ 3.4 × 10 addresses . </P> <P> In addition, the IPv4 address space is poorly allocated; in 2011, approximately 14% of all available addresses were utilized . While these numbers are large, it was not the intent of the designers of the IPv6 address space to assure geographical saturation with usable addresses . Rather, the longer addresses simplify allocation of addresses, enable efficient route aggregation, and allow implementation of special addressing features . In IPv4, complex Classless Inter-Domain Routing (CIDR) methods were developed to make the best use of the small address space . The standard size of a subnet in IPv6 is 2 addresses, the square of the size of the entire IPv4 address space . Thus, actual address space utilization rates will be small in IPv6, but network management and routing efficiency are improved by the large subnet space and hierarchical route aggregation . </P> <P> Renumbering an existing network for a new connectivity provider with different routing prefixes is a major effort with IPv4 . With IPv6, however, changing the prefix announced by a few routers can in principle renumber an entire network, since the host identifiers (the least - significant 64 bits of an address) can be independently self - configured by a host . </P>

A requirement of the internet protocol version 6 that allows encryption is called