215 lines
5.2 KiB
Groff
215 lines
5.2 KiB
Groff
.Dd June 1, 2017
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.Dt INET 4
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.Os
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.Sh NAME
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.Nm inet
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.Nd internet protocol family
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.Sh SYNOPSIS
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.In sys/socket.h
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.In netinet/in.h
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.Pp
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.Fd #define AF_INET 1
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.Bd -literal
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typedef uint16_t sa_family_t;
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typedef uint16_t in_port_t;
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typedef uint32_t in_addr_t;
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struct in_addr {
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in_addr_t s_addr;
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};
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struct sockaddr_in {
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sa_family_t sin_family;
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in_port_t sin_port;
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struct in_addr sin_addr;
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};
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.Ed
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.Sh DESCRIPTION
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The Internet Protocol version 4 protocol family is a set of protocols using the
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Internet Protocol version 4
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.Xr ip 4
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as the network layer.
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.Dv SOCK_STREAM
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sockets are provided by the Transmission Control Protocol
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.Xr tcp 4 .
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.Dv SOCK_DGRAM
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sockets are provided by the User Datagram Protocol
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.Xr udp 4 .
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.Pp
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Hosts are addressed with a four byte Internet Protocol (IP) address stored in a
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.Vt struct in_addr
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in network byte order.
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IP addresses are notated by
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the decimal byte values interspaced with periods, e.g. 192.0.2.255.
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Subnetworks are ranges of IP addresses given by a starting IP address along with
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how many leading bits (most significant bit first) of the IP address are common
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to the network (the prefix), the first address of the the subnetwork is the
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prefix with the remaining bits set to zero, and the last address is the prefix
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with the
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remaining bits set to one.
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A subnetwork can be denoted by the starting IP address and the leading bits,
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e.g. 198.51.100.0/24 spans from 198.51.100.0 to 198.51.100.255.
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The subnet mask of a subnetwork is an IP address with the bits set that belong
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to the network prefix, e.g. the subnet mask of 203.0.113.0/24 is 255.255.255.0.
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The subnetworks 192.0.2.0/24 (TEST-NET-1), 198.51.100.0/24 (TEST-NET-2), and
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203.0.113.0/24 (TEST-NET-2) are reserved for documentation.
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The last address in a network is normally the broadcast address for the network.
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.Pp
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Services are addressed
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with a 16-bit byte port number in a
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.Vt in_port_t
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in network byte order.
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.Pp
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Sockets are addressed with the combination of a host address and port number
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stored in a
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.Vt struct sockaddr_in
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where
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.Va sin_family
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is set to
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.Dv AF_INET ,
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.Va sin_port
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is set to the 16-bit port number in network byte order, and
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.Va sin_addr
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is set to the host address in network byte order.
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.Pp
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.Va sin_port
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can be set to
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.Li 0
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(converted to network byte order)
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to request
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.Xr bind 2
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allocate a port.
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Port
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.Li 0
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is not valid as a destination port.
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.Pp
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.Va sin_addr.s_addr
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can be set to
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.Dv INADDR_ANY
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.Pq 0.0.0.0
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(converted to network byte order) to mean an unspecified address.
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When a socket is bound to the address
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.Dv INADDR_ANY ,
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messages are accepted from any address.
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In
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.Xr connect 2
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and
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.Xr sendto 2 ,
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the destination address
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.Dv INADDR_ANY
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means the current host.
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.Pp
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.Va sin_addr.s_addr
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can be set to
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.Dv INADDR_BROADCAST
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.Pq 255.255.255.255
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(converted to network byte order),
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the broadcast address of the local network.
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.Pp
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.Va sin_addr.s_addr
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can be set to
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.Dv INADDR_LOOPBACK
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.Pq 127.0.0.1
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(converted to network byte order), the address of the loopback interface
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.Xr lo 4 .
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.Dv INADDR_LOOPMASK
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.Pq 255.0.0.0
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contains the subnet mask of the loopback interface.
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.Pp
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Sockets of this protocol family can be created by passing
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.Dv AF_INET
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as the
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.Fa domain
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parameter of
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.Xr socket 2 .
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.Pp
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The network byte order is big-endian.
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.Pp
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IP addresses in 32-bit integer format in the host endian can be converted
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to network byte order using
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.Xr htobe32 3
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or
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.Xr htonl 3
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and back using
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.Xr be32toh 3
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or
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.Xr ntohl 3 .
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.Pp
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Port numbers in 16-bit integer format in the host endian can be converted
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to network byte order using
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.Xr htobe16 3
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or
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.Xr htons 3
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and back using
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.Xr be16toh 3
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or
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.Xr ntohs 3 .
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.Pp
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.Xr inet_pton 3
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can be used to convert an IP address from textual representation to binary
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representation.
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.Xr inet_ntop 3
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can be used to convert an IP address from binary representation to textual
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representation.
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.Sh EXAMPLES
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This example manually constructs and deconstructs a
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.Vt struct inaddr_in .
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.Bd -literal
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struct sockaddr_in saddr;
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memset(&saddr, 0, sizeof(saddr));
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saddr.sin_family = AF_INET;
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saddr.sin_addr.s_addr = htobe32(0xC0000201); /* 192.0.2.1 */
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saddr.sin_port = htobe16(1234);
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sa_family_t family = saddr.sin_family;
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in_addr_t addr = be32toh(saddr.sin_addr.s_addr);
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in_port_t port = be16toh(saddr.sin_port);
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.Ed
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.Sh COMPATIBILITY
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On some operating systems,
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.Vt struct sockaddr_in
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may contain padding and additional members and the structure should be
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initialized to zero prior to initializing its members.
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.Sh SEE ALSO
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.Xr socket 2 ,
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.Xr arp 4 ,
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.Xr icmp 4 ,
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.Xr ip 4 ,
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.Xr ping 4 ,
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.Xr tcp 4 ,
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.Xr udp 4 ,
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.Xr kernel 7
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.Sh STANDARDS
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.Rs
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.%A J. Postel (ed.)
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.%D September 1981
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.%R STD 5
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.%R RFC 791
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.%T Internet Protocol - DARPA Internet Program Protocol Specification
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.%Q USC/Information Sciences Institute
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.Re
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.Pp
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.Rs
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.%A Internet Engineering Task Force
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.%A J. Arkko
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.%A M. Cotton
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.%A L. Vegoda
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.%D January 2010
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.%R RFC 5737
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.%T IPv4 Address Blocks Reserved for Documentation
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.%Q Ericsson
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.%Q ICANN
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.Re
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.Pp
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The protocol family programming interface conforms to
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.St -p1003.1-2008 .
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.Sh BUGS
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The network stack implementation is incomplete and has known bugs.
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See the protocol manual pages for more information.
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.Pp
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The 4-byte address space allows only a maximum of 4294967296 addresses and is
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being exhausted.
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The Internet Protocol version 6 replaces version 4 and provides a 16-byte
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address space instead.
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