IPVersion

IPVersion is a designation used in networking to indicate which version of the Internet Protocol is being used for a given packet, address, or communication session. The two main versions in use today are IPv4 and IPv6. Software, routers, and protocols use IPVersion to determine how to interpret addresses, headers, and payloads, and to apply appropriate routing and security rules.

IPv4 is the fourth version; uses 32-bit addresses, commonly written in dotted-decimal notation. The IPv4 header includes fields such as version, header length, total length, TTL, protocol, source and destination addresses. IPv4 supports fragmentation and has limited address space, leading to the deployment of network address translation to conserve addresses.

IPv6 is the successor with 128-bit addresses, written in hexadecimal colon-separated notation. IPv6 headers are simplified, with fixed size and a different set of fields; fragmentation is handled by the sending host or at the endpoints, not by routers. IPv6 provides improved support for autoconfiguration, neighbor discovery, and built-in support for IPsec in theory, though deployment varies. The version field in IPv6 headers is 6.

Transition and interoperability: To enable coexistence, techniques such as dual-stack deployments, tunneling mechanisms (6to4, Teredo) and translation approaches (NAT64, NPTv6) are used. In software, IPVersion is typically represented as an enumerated type or constant values (4 or 6) alongside other addressing information, and routing stacks use it to select appropriate processing paths.

See also: Internet Protocol, IPv4, IPv6, IP address, routing.