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Internet Protocol Version 4 (IPv4) is the fourth revision of the Internet Protocol and a widely used protocol in data communication over different kinds of networks. IPv4 is a connectionless protocol used in packet-switched layer networks, such as Ethernet. It provides the logical connection between network devices by providing identification for each device. There are many ways to configure IPv4 with all kinds of devices – including manual and automatic configurations – depending on the network type.
IPv4 is based on the best-effort model. This model guarantees neither delivery nor avoidance of duplicate delivery; these aspects are handled by the upper layer transport.
IPv4 is defined and specified in IETF publication RFC 791. It is used in the packet-switched link layer in the OSI model.
IPv4 uses 32-bit addresses for Ethernet communication in five classes: A, B, C, D and E. Classes A, B and C have a different bit length for addressing the network host. Class D addresses are reserved for multicasting, while class E addresses are reserved for future use.
Class A has subnet mask 255.0.0.0 or /8, B has subnet mask 255.255.0.0 or /16 and class C has subnet mask 255.255.255.0 or /24. For example, with a /16 subnet mask, the network 192.168.0.0 may use the address range of 192.168.0.0 to 192.168.255.255. Network hosts can take any address from this range; however, address 192.168.255.255 is reserved for broadcast within the network. The maximum number of host addresses IPv4 can assign to end users is 232.
IPv6 presents a standardized solution to overcome IPv4's limiations. Because of its 128-bit address length, it can define up to 2,128 addresses.