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+.\"     $OpenBSD: inet.3,v 1.22 2008/12/09 19:38:38 otto Exp $
+.\"     $NetBSD: inet.3,v 1.7 1997/06/18 02:25:24 lukem Exp $
+.\"
+.\" Copyright (c) 1983, 1990, 1991, 1993
+.\"     The Regents of the University of California.  All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"     @(#)inet.3      8.1 (Berkeley) 6/4/93
+.\"
+.Dd $Mdocdate: December 9 2008 $
+.Dt INET 3
+.Os
+.Sh NAME
+.Nm inet_addr ,
+.Nm inet_aton ,
+.Nm inet_lnaof ,
+.Nm inet_makeaddr ,
+.Nm inet_netof ,
+.Nm inet_network ,
+.Nm inet_ntoa ,
+.Nm inet_ntop ,
+.Nm inet_pton
+.Nd Internet address manipulation routines
+.Sh SYNOPSIS
+.Fd #include <sys/types.h>
+.Fd #include <sys/socket.h>
+.Fd #include <netinet/in.h>
+.Fd #include <arpa/inet.h>
+.Ft in_addr_t
+.Fn inet_addr "const char *cp"
+.Ft int
+.Fn inet_aton "const char *cp" "struct in_addr *addr"
+.Ft in_addr_t
+.Fn inet_lnaof "struct in_addr in"
+.Ft struct in_addr
+.Fn inet_makeaddr "in_addr_t net" "in_addr_t lna"
+.Ft in_addr_t
+.Fn inet_netof "struct in_addr in"
+.Ft in_addr_t
+.Fn inet_network "const char *cp"
+.Ft char *
+.Fn inet_ntoa "struct in_addr in"
+.Ft const char *
+.Fn inet_ntop "int af" "const void *src" "char *dst" "socklen_t size"
+.Ft int
+.Fn inet_pton "int af" "const char *src" "void *dst"
+.Sh DESCRIPTION
+The routines
+.Fn inet_aton ,
+.Fn inet_addr ,
+and
+.Fn inet_network
+interpret character strings representing
+numbers expressed in the Internet standard
+.Dq dot
+notation.
+The
+.Fn inet_pton
+function converts a presentation format address (that is, printable form
+as held in a character string) to network format (usually a
+.Li struct in_addr
+or some other internal binary representation, in network byte order).
+It returns 1 if the address was valid for the specified address family;
+0 if the address wasn't parseable in the specified address family; or \-1
+if some system error occurred (in which case
+.Va errno
+will have been set).
+This function is presently valid for
+.Dv AF_INET
+and
+.Dv AF_INET6 .
+The
+.Fn inet_aton
+routine interprets the specified character string as an Internet address,
+placing the address into the structure provided.
+It returns 1 if the string was successfully interpreted,
+or 0 if the string was invalid.
+The
+.Fn inet_addr
+and
+.Fn inet_network
+functions return numbers suitable for use
+as Internet addresses and Internet network
+numbers, respectively.
+.Pp
+The function
+.Fn inet_ntop
+converts an address from network format (usually a
+.Li struct in_addr
+or some other binary form, in network byte order) to presentation format
+(suitable for external display purposes).
+It returns
+.Dv NULL
+if a system
+error occurs (in which case,
+.Va errno
+will have been set), or it returns a pointer to the destination string.
+The routine
+.Fn inet_ntoa
+takes an Internet address and returns an
+ASCII string representing the address in dot notation.
+The routine
+.Fn inet_makeaddr
+takes an Internet network number and a local
+network address and constructs an Internet address
+from it.
+The routines
+.Fn inet_netof
+and
+.Fn inet_lnaof
+break apart Internet host addresses, returning
+the network number and local network address part,
+respectively.
+.Pp
+All Internet addresses are returned in network
+order (bytes ordered from left to right).
+All network numbers and local address parts are
+returned as machine format integer values.
+.Sh INTERNET ADDRESSES (IP VERSION 4)
+Values specified using dot notation take one of the following forms:
+.Bd -literal -offset indent
+a.b.c.d
+a.b.c
+a.b
+a
+.Ed
+.Pp
+When four parts are specified, each is interpreted
+as a byte of data and assigned, from left to right,
+to the four bytes of an Internet address.
+Note that when an Internet address is viewed as a 32-bit
+integer quantity on a system that uses little-endian
+byte order
+(such as the Intel 386, 486 and Pentium processors)
+the bytes referred to above appear as
+.Dq Li d.c.b.a .
+That is, little-endian bytes are ordered from right to left.
+.Pp
+When a three part address is specified, the last
+part is interpreted as a 16-bit quantity and placed
+in the rightmost two bytes of the network address.
+This makes the three part address format convenient
+for specifying Class B network addresses as
+.Dq Li 128.net.host .
+.Pp
+When a two part address is supplied, the last part
+is interpreted as a 24-bit quantity and placed in
+the rightmost three bytes of the network address.
+This makes the two part address format convenient
+for specifying Class A network addresses as
+.Dq Li net.host .
+.Pp
+When only one part is given, the value is stored
+directly in the network address without any byte
+rearrangement.
+.Pp
+All numbers supplied as
+.Dq parts
+in a dot notation
+may be decimal, octal, or hexadecimal, as specified
+in the C language (i.e., a leading 0x or 0X implies
+hexadecimal; a leading 0 implies octal;
+otherwise, the number is interpreted as decimal).
+.Sh INTERNET ADDRESSES (IP VERSION 6)
+In order to support scoped IPv6 addresses,
+.Xr getaddrinfo 3
+and
+.Xr getnameinfo 3
+are recommended rather than the functions presented here.
+.Pp
+The presentation format of an IPv6 address is given in RFC 2373:
+.Pp
+There are three conventional forms for representing IPv6 addresses as
+text strings:
+.Bl -enum
+.It
+The preferred form is x:x:x:x:x:x:x:x, where the 'x's are the
+hexadecimal values of the eight 16-bit pieces of the address.
+Examples:
+.Bd -literal -offset indent
+FEDC:BA98:7654:3210:FEDC:BA98:7654:3210
+1080:0:0:0:8:800:200C:417A
+.Ed
+.Pp
+Note that it is not necessary to write the leading zeros in an
+individual field, but there must be at least one numeral in
+every field (except for the case described in 2.).
+.It
+Due to the method of allocating certain styles of IPv6
+addresses, it will be common for addresses to contain long
+strings of zero bits.
+In order to make writing addresses
+containing zero bits easier, a special syntax is available to
+compress the zeros.
+The use of
+.Dq \&:\&:
+indicates multiple groups
+of 16 bits of zeros.
+The
+.Dq \&:\&:
+can only appear once in an
+address.
+The
+.Dq \&:\&:
+can also be used to compress the leading and/or trailing zeros in an address.
+.Pp
+For example the following addresses:
+.Bd -literal -offset indent
+1080:0:0:0:8:800:200C:417A  a unicast address
+FF01:0:0:0:0:0:0:43         a multicast address
+0:0:0:0:0:0:0:1             the loopback address
+0:0:0:0:0:0:0:0             the unspecified addresses
+.Ed
+.Pp
+may be represented as:
+.Bd -literal -offset indent
+1080::8:800:200C:417A       a unicast address
+FF01::43                    a multicast address
+::1                         the loopback address
+::                          the unspecified addresses
+.Ed
+.It
+An alternative form that is sometimes more convenient when
+dealing with a mixed environment of IPv4 and IPv6 nodes is
+x:x:x:x:x:x:d.d.d.d, where the 'x's are the hexadecimal values
+of the six high-order 16-bit pieces of the address, and the 'd's
+are the decimal values of the four low-order 8-bit pieces of the
+address (standard IPv4 representation).
+Examples:
+.Bd -literal -offset indent
+0:0:0:0:0:0:13.1.68.3
+0:0:0:0:0:FFFF:129.144.52.38
+.Ed
+.Pp
+or in compressed form:
+.Bd -literal -offset indent
+::13.1.68.3
+::FFFF:129.144.52.38
+.Ed
+.El
+.Sh DIAGNOSTICS
+The constant
+.Dv INADDR_NONE
+is returned by
+.Fn inet_addr
+and
+.Fn inet_network
+for malformed requests.
+.Sh SEE ALSO
+.Xr byteorder 3 ,
+.Xr gethostbyname 3 ,
+.Xr getnetent 3 ,
+.Xr inet_net 3 ,
+.Xr hosts 5 ,
+.Xr networks 5
+.Rs
+.%R RFC 2373
+.%D July 1998
+.%T "IP Version 6 Addressing Architecture"
+.Re
+.Rs
+.%R RFC 3493
+.%D February 2003
+.%T "Basic Socket Interface Extensions for IPv6"
+.Re
+.Sh STANDARDS
+The
+.Nm inet_ntop
+and
+.Nm inet_pton
+functions conform to the IETF IPv6 BSD API and address formatting
+specifications.
+Note that
+.Nm inet_pton
+does not accept 1-, 2-, or 3-part dotted addresses; all four parts
+must be specified.
+This is a narrower input set than that accepted by
+.Nm inet_aton .
+.Sh HISTORY
+The
+.Nm inet_addr ,
+.Nm inet_network ,
+.Nm inet_makeaddr ,
+.Nm inet_lnaof ,
+and
+.Nm inet_netof
+functions appeared in
+.Bx 4.2 .
+The
+.Nm inet_aton
+and
+.Nm inet_ntoa
+functions appeared in
+.Bx 4.3 .
+The
+.Nm inet_pton
+and
+.Nm inet_ntop
+functions appeared in BIND 4.9.4.
+.Sh BUGS
+The value
+.Dv INADDR_NONE
+(0xffffffff) is a valid broadcast address, but
+.Fn inet_addr
+cannot return that value without indicating failure.
+Also,
+.Fn inet_addr
+should have been designed to return a
+.Li struct in_addr .
+The newer
+.Fn inet_aton
+function does not share these problems, and almost all existing code
+should be modified to use
+.Fn inet_aton
+instead.
+.Pp
+The problem of host byte ordering versus network byte ordering is
+confusing.
+.Pp
+The string returned by
+.Fn inet_ntoa
+resides in a static memory area.