netinet_in.h(0P)	   POSIX Programmer's Manual	      netinet_in.h(0P)

PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the corresponding
       Linux manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

NAME
       netinet/in.h — Internet address family

SYNOPSIS
       #include <netinet/in.h>

DESCRIPTION
       The <netinet/in.h> header shall define the following types:

       in_port_t Equivalent to the type uint16_t as described in <inttypes.h>.

       in_addr_t Equivalent to the type uint32_t as described in <inttypes.h>.

       The <netinet_in.h> header shall define the sa_family_t type as
       described in <sys/socket.h>.

       The <netinet_in.h> header shall define the uint8_t and uint32_t types
       as described in <inttypes.h>.  Inclusion of the <netinet/in.h> header
       may also make visible all symbols from <inttypes.h> and <sys/socket.h>.

       The <netinet/in.h> header shall define the in_addr structure, which
       shall include at least the following member:


	   in_addr_t  s_addr

       The <netinet/in.h> header shall define the sockaddr_in structure, which
       shall include at least the following members:


	   sa_family_t	   sin_family	AF_INET.
	   in_port_t	   sin_port	Port number.
	   struct in_addr  sin_addr	IP address.

       The sin_port and sin_addr members shall be in network byte order.

       The sockaddr_in structure is used to store addresses for the Internet
       address family.	Pointers to this type shall be cast by applications to
       struct sockaddr * for use with socket functions.

       The <netinet/in.h> header shall define the in6_addr structure, which
       shall include at least the following member:


	   uint8_t s6_addr[16]

       This array is used to contain a 128-bit IPv6 address, stored in network
       byte order.

       The <netinet/in.h> header shall define the sockaddr_in6 structure,
       which shall include at least the following members:


	   sa_family_t	    sin6_family	   AF_INET6.
	   in_port_t	    sin6_port	   Port number.
	   uint32_t	    sin6_flowinfo  IPv6 traffic class and flow information.
	   struct in6_addr  sin6_addr	   IPv6 address.
	   uint32_t	    sin6_scope_id  Set of interfaces for a scope.

       The sin6_port and sin6_addr members shall be in network byte order.

       Prior to calling a function in this standard which reads values from a
       sockaddr_in6 structure (for example, bind() or connect()), the
       application shall ensure that all members of the structure, including
       any additional non-standard members, if any, are initialized.  If the
       sockaddr_in6 structure has a non-standard member, and that member has a
       value other than the value that would result from default
       initialization, the behavior of any function in this standard that
       reads values from the sockaddr_in6 structure is implementation-defined.
       All functions in this standard that return data in a sockaddr_in6
       structure (for example, getaddrinfo() or accept()) shall initialize the
       structure in a way that meets the above requirements, and shall ensure
       that each non-standard member, if any, has a value that produces the
       same behavior as default initialization would in all functions in this
       standard which read values from a sockaddr_in6 structure.

       The sin6_scope_id field is a 32-bit integer that identifies a set of
       interfaces as appropriate for the scope of the address carried in the
       sin6_addr field. For a link scope sin6_addr, the application shall
       ensure that sin6_scope_id is a link index. For a site scope sin6_addr,
       the application shall ensure that sin6_scope_id is a site index. The
       mapping of sin6_scope_id to an interface or set of interfaces is
       implementation-defined.

       The <netinet/in.h> header shall declare the following external
       variable:


	   const struct in6_addr in6addr_any

       This variable is initialized by the system to contain the wildcard IPv6
       address. The <netinet/in.h> header also defines the IN6ADDR_ANY_INIT
       macro. This macro must be constant at compile time and can be used to
       initialize a variable of type struct in6_addr to the IPv6 wildcard
       address.

       The <netinet/in.h> header shall declare the following external
       variable:


	   const struct in6_addr in6addr_loopback

       This variable is initialized by the system to contain the loopback IPv6
       address. The <netinet/in.h> header also defines the
       IN6ADDR_LOOPBACK_INIT macro. This macro must be constant at compile
       time and can be used to initialize a variable of type struct in6_addr
       to the IPv6 loopback address.

       The <netinet/in.h> header shall define the ipv6_mreq structure, which
       shall include at least the following members:


	   struct in6_addr  ipv6mr_multiaddr  IPv6 multicast address.
	   unsigned	    ipv6mr_interface  Interface index.

       The <netinet/in.h> header shall define the following symbolic constants
       for use as values of the level argument of getsockopt() and
       setsockopt():

       IPPROTO_IP      Internet protocol.

       IPPROTO_IPV6    Internet Protocol Version 6.

       IPPROTO_ICMP    Control message protocol.

       IPPROTO_RAW     Raw IP Packets Protocol.

       IPPROTO_TCP     Transmission control protocol.

       IPPROTO_UDP     User datagram protocol.

       The <netinet/in.h> header shall define the following symbolic constant
       for use as a local address in the structure passed to bind():

       INADDR_ANY      IPv4 wildcard address.

       The <netinet/in.h> header shall define the following symbolic constant
       for use as a destination address in the structures passed to connect(),
       sendmsg(), and sendto():

       INADDR_BROADCAST
		       IPv4 broadcast address.

       The <netinet/in.h> header shall define the following symbolic constant,
       with the value specified, to help applications declare buffers of the
       proper size to store IPv4 addresses in string form:

       INET_ADDRSTRLEN 16. Length of the string form for IP.

       The htonl(), htons(), ntohl(), and ntohs() functions shall be available
       as described in <arpa/inet.h>.  Inclusion of the <netinet/in.h> header
       may also make visible all symbols from <arpa/inet.h>.

       The <netinet/in.h> header shall define the following symbolic constant,
       with the value specified, to help applications declare buffers of the
       proper size to store IPv6 addresses in string form:

       INET6_ADDRSTRLEN
		       46. Length of the string form for IPv6.

       The <netinet/in.h> header shall define the following symbolic
       constants, with distinct integer values, for use in the option_name
       argument in the getsockopt() or setsockopt() functions at protocol
       level IPPROTO_IPV6:

       IPV6_JOIN_GROUP Join a multicast group.

       IPV6_LEAVE_GROUP
		       Quit a multicast group.

       IPV6_MULTICAST_HOPS
		       Multicast hop limit.

       IPV6_MULTICAST_IF
		       Interface to use for outgoing multicast packets.

       IPV6_MULTICAST_LOOP
		       Multicast packets are delivered back to the local
		       application.

       IPV6_UNICAST_HOPS
		       Unicast hop limit.

       IPV6_V6ONLY     Restrict AF_INET6 socket to IPv6 communications only.

       The <netinet/in.h> header shall define the following macros that test
       for special IPv6 addresses. Each macro is of type int and takes a
       single argument of type const struct in6_addr *:

       IN6_IS_ADDR_UNSPECIFIED
	     Unspecified address.

       IN6_IS_ADDR_LOOPBACK
	     Loopback address.

       IN6_IS_ADDR_MULTICAST
	     Multicast address.

       IN6_IS_ADDR_LINKLOCAL
	     Unicast link-local address.

       IN6_IS_ADDR_SITELOCAL
	     Unicast site-local address.

       IN6_IS_ADDR_V4MAPPED
	     IPv4 mapped address.

       IN6_IS_ADDR_V4COMPAT
	     IPv4-compatible address.

       IN6_IS_ADDR_MC_NODELOCAL
	     Multicast node-local address.

       IN6_IS_ADDR_MC_LINKLOCAL
	     Multicast link-local address.

       IN6_IS_ADDR_MC_SITELOCAL
	     Multicast site-local address.

       IN6_IS_ADDR_MC_ORGLOCAL
	     Multicast organization-local address.

       IN6_IS_ADDR_MC_GLOBAL
	     Multicast global address.

       The following sections are informative.

APPLICATION USAGE
       Although applications are required to initialize all members (including
       any non-standard ones) of a sockaddr_in6 structure, the same is not
       required for the sockaddr_in structure, since historically many
       applications only initialized the standard members. Despite this,
       applications are encouraged to initialize sockaddr_in structures in a
       manner similar to the required initialization of sockaddr_in6
       structures.

       Although it is common practice to initialize a sockaddr_in6 structure
       using:


	   struct sockaddr_in6 sa;
	   memset(&sa, 0, sizeof sa);

       this method is not portable according to this standard, because the
       structure can contain pointer or floating-point members that are not
       required to have an all-bits-zero representation after default
       initialization. Portable methods make use of default initialization;
       for example:


	   struct sockaddr_in6 sa = { 0 };

       or:


	   static struct sockaddr_in6 sa_init;
	   struct sockaddr_in6 sa = sa_init;

       A future version of this standard may require that a pointer object
       with an all-bits-zero representation is a null pointer, and that
       sockaddr_in6 does not have any floating-point members if a floating-
       point object with an all-bits-zero representation does not have the
       value 0.0.

RATIONALE
       The INADDR_ANY and INADDR_BROADCAST values are byte-order-neutral and
       thus their byte order is not specified. Many implementations have
       additional constants as extensions, such as INADDR_LOOPBACK, that are
       not byte-order-neutral. Traditionally, these constants are in host byte
       order, requiring the use of htonl() when using them in a sockaddr_in
       structure.

FUTURE DIRECTIONS
       None.

SEE ALSO
       Section 4.10, Host and Network Byte Orders, <arpa_inet.h>,
       <inttypes.h>, <sys_socket.h>

       The System Interfaces volume of POSIX.1‐2017, connect(), getsockopt(),
       htonl(), sendmsg(), sendto(), setsockopt()

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  In the event of any discrepancy between this version and the
       original IEEE and The Open Group Standard, the original IEEE and The
       Open Group Standard is the referee document. The original Standard can
       be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2017		      netinet_in.h(0P)