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The term subnet mask is only used within IPv4. Both IP versions however use the CIDR concept and notation. In this, the IP address is followed by a slash and the number (in decimal) of bits used for the network part, also called the routing prefix. For example, an IPv4 address and its subnet mask may be 192.0.2.1 and 255.255.255.0, respectively.
Some large / 8 blocks of IPv4 addresses, the former Class A network blocks, are assigned in whole to single organizations or related groups of organizations, either by the Internet Corporation for Assigned Names and Numbers (ICANN), through the Internet Assigned Numbers Authority (IANA), or a regional Internet registry.
The result of the bitwise AND operation of IP address and the subnet mask is the network prefix 192.0.2.0. The host part, which is 130, is derived by the bitwise AND operation of the address and the ones' complement of the subnet mask.
Special address blocks Address block Address range Number of addresses Scope Description 0.0.0.0/8 0.0.0.0–0.255.255.255 16 777 216: Software Current (local, "this") network [1]
The Internet Engineering Task Force (IETF) has reserved the IPv4 address block 169.254.0.0 / 16 (169.254.0.0 – 169.254.255.255) for link-local addressing. [1] The entire range may be used for this purpose, except for the first 256 and last 256 addresses (169.254.0.0 / 24 and 169.254.255.0 / 24), which are reserved for future use and must not be selected by a host using this dynamic ...
As shown in the example below, in order to calculate the directed broadcast address to transmit a packet to an entire IPv4 subnet using the private IP address space 172.16.0.0 / 12, which has the subnet mask 255.240.0.0, the broadcast address is calculated as 172.16.0.0 bitwise ORed with 0.15.255.255 = 172.31.255.255. Directed broadcasts always ...
Instead, an address in the 100.64.0.0 / 10 range is assigned on the CPE's Internet-facing interface, and this address is translated again to one of the public IPv4 addresses of the ISP's core routers. Using shared address space allows ISPs to continue to use IPv4 as they were used to.
For link-local addressing, IPv4 uses the special block 169.254.0.0 / 16, [1] while IPv6 hosts use the prefix fe80:: / 10. More commonly addresses are assigned by a DHCP server, often built into common networking hardware like computer hosts or routers. Most IPv4 hosts use link-local addressing only as a last resort when a DHCP server is ...