Internet Protocol version 4 is the fourth iteration of the Internet Protocol (IP) and it is the first version of the protocol to be widely deployed. IPv4 is the dominant network layer protocol on the internet and when ignoring its successor IPv6 it is the only protocol used on the internet. IPv4 is a data-oriented protocol to be used on a packet switched internetwork (e.g., Ethernet). It is a best effort protocol in that it doesn’t guarantee delivery. It doesn’t make any guarantees on the correctness of the data; it may result in duplicated packets and/or packets out-of-order. All of these things are addressed by an upper layer protocol (e.g., TCP, UDP). The entire purpose of IP is to provide unique global computer addressing to ensure that two computers over the internet can uniquely identify one another.
IPv4 Address Architecture
In the case of IPv4 there have been a number of iterations of address architecture, starting with the original specification of the so-called 8/24 split, using 8 bites to identify the network and 24 bits to identify the end host, then the adoption of the Class-based address system, to the current classless setup, where addresses in the range 0.0.0.0 through to 188.8.131.52 are assigned for use as global unicast addresses, addresses in the range 184.108.40.206 though to 220.127.116.11 are assigned for multicast use, and the remaining addresses, from 240.0.0.0 through to 255.255.255.254 are reserved for future definition by the IETF [RFC3330].
IPv4 uses 32-bit (4-byte) addresses, which limits the address space to 4,294,967,296 possible unique addresses. However, many are reserved for special purposes such as private networks (~18 million addresses) or multicast addresses (~1 million addresses). This reduces the number of addresses that can be allocated as public Internet addresses and as the number of addresses available is consumed, an IPv4 address shortage appears to be inevitable in the long run.
This limitation has helped stimulate the push towards IPv6, which is currently in the early stages of deployment and is currently the only contender to replace IPv4.
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