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IPv6 addresses are assigned to organizations in much larger blocks as compared to IPv4 address assignments—the recommended allocation is a / 48 block which contains 2 80 addresses, being 2 48 or about 2.8 × 10 14 times larger than the entire IPv4 address space of 2 32 addresses and about 7.2 × 10 16 times larger than the / 8 blocks of IPv4 ...
Such a dual-stack DNS server holds IPv4 addresses in the A records and IPv6 addresses in the AAAA records. Depending on the destination that is to be resolved, a DNS name server may return an IPv4 or IPv6 IP address, or both. A default address selection mechanism, or preferred protocol, needs to be configured either on hosts or the DNS server.
At the top level, the IP address pool is managed by the Internet Assigned Numbers Authority (IANA). The total IPv4 address pool contains 4 294 967 296 (2 32 ) addresses, while the size of the IPv6 address pool is 2 128 ( 340 282 366 920 938 463 463 374 607 431 768 211 456 ) addresses.
A public IP address is a globally routable unicast IP address, meaning that the address is not an address reserved for use in private networks, such as those reserved by RFC 1918, or the various IPv6 address formats of local scope or site-local scope, for example for link-local addressing. Public IP addresses may be used for communication ...
Used for link-local addresses [5] between two hosts on a single link when no IP address is otherwise specified, such as would have normally been retrieved from a DHCP server 172.16.0.0/12 172.16.0.0–172.31.255.255
Some address space previously reserved by IANA has been added to the available pool. There have been proposals to use the class E network range of IPv4 addresses [76] [77] (which would add 268.4 million IP addresses to the available pool) but many computer and router operating systems and firmware do not allow the use of these addresses.
Both the IPv4 and the IPv6 specifications define private IP address ranges. [ 1 ] [ 2 ] Most Internet service providers (ISPs) allocate only a single publicly routable IPv4 address to each residential customer, but many homes have more than one computer , smartphone , or other Internet-connected device.
This means that 256 /8 address blocks fit into the entire IPv4 space. As IPv4 address exhaustion has advanced to its final stages, some organizations, such as Stanford University , formerly using 36.0.0.0 / 8 , have returned their allocated blocks (in this case to APNIC ) to assist in the delay of the exhaustion date.