IPv6

IPv6 is the sixth version of the Internet Protocol, designed to replace IPv4 and address limitations such as address exhaustion, routing scalability, and policy features. It uses 128-bit addresses, providing a vastly larger address space and enabling more flexible addressing and routing options.

Addressing and autoconfiguration: IPv6 addresses are 128 bits and written as eight groups of four hexadecimal digits separated by colons. They can be abbreviated by omitting leading zeros and collapsing consecutive zeros with a double colon once in an address. IPv6 defines unicast, multicast, and anycast address types; link-local addresses (fe80::/10) are used on a single link, while global unicast addresses are routable on the Internet. Automatic configuration uses Stateless Address Autoconfiguration (SLAAC) with router advertisements, or DHCPv6. Broadcast is not defined; multicast replaces its functions.

Header and routing: The IPv6 base header is 40 bytes with a streamlined structure and fewer optional extension headers. It includes fields such as flow label and next header. Routers do not fragment packets; fragmentation is performed by the end hosts. The simplified header and extended options aim to improve processing efficiency and routing scalability.

Transition and deployment: IPv6 and IPv4 can operate simultaneously (dual-stack). Transition mechanisms enable IPv6 deployment over existing networks, including tunneling (6to4, ISATAP, Teredo, 6in4) and translation (NAT64). Adoption has grown since the 2010s, but full global ubiquity is not universal, and many networks still rely on IPv4.

Security and policy: IPsec support is available with IPv6 but not required for operation. IPv6 includes features that support privacy, such as temporary addresses, and requires careful configuration to address new attack surfaces and security considerations.