sockaddrin6

sockaddr_in6 is the IPv6 socket address structure used in POSIX-style networking. It is defined in netinet/in.h and is used with socket APIs that operate on socket addresses, such as bind, connect, accept, sendto, and recvfrom. The structure holds the information necessary to identify an IPv6 endpoint.

The structure contains the following fields:

- sin6_family: the address family, which must be AF_INET6.

- sin6_port: the port number in network byte order (use htons to convert from host byte order).

- sin6_flowinfo: a 32-bit field for IPv6 flow information, used for quality-of-service features.

- sin6_addr: the 128-bit IPv6 address, represented by the in6_addr structure (often accessed as an array of 16 bytes).

- sin6_scope_id: a platform-dependent scope identifier, used to specify the interface for link-local addresses or other scoped addresses.

The in6_addr type holds the actual IPv6 address, and common helpers such as inet_pton and inet_ntop convert between textual and binary forms. Programs frequently populate sockaddr_in6 via getaddrinfo or by constructing the structure directly, setting sin6_family to AF_INET6, sin6_port with htons, and sin6_addr with a valid IPv6 address. For listening sockets, sin6_addr is often set to in6addr_any to bind on all interfaces, while sin6_scope_id may be set for link-local addresses to specify the interface.

sockaddr_in6 is the IPv6 counterpart to sockaddr_in used for IPv4 (AF_INET). Its size and layout are specific to IPv6 and may differ across platforms, but the required semantics—family, port, address, and optional scope—remain consistent for enabling IPv6 networking.