475 lines
10 KiB
Groff
475 lines
10 KiB
Groff
.\" $KAME: getipnodebyname.3,v 1.6 2000/08/09 21:16:17 itojun Exp $
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.\"
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.\" Copyright (c) 1983, 1987, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" From: @(#)gethostbyname.3 8.4 (Berkeley) 5/25/95
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.\" $FreeBSD$
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.\"
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.Dd August 6, 2004
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.Dt GETIPNODEBYNAME 3
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.Os
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.\"
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.Sh NAME
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.Nm getipnodebyname ,
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.Nm getipnodebyaddr ,
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.Nm freehostent
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.Nd nodename-to-address and address-to-nodename translation
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.\"
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/socket.h
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.In netdb.h
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.Ft "struct hostent *"
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.Fn getipnodebyname "const char *name" "int af" "int flags" "int *error_num"
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.Ft "struct hostent *"
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.Fn getipnodebyaddr "const void *src" "size_t len" "int af" "int *error_num"
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.Ft void
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.Fn freehostent "struct hostent *ptr"
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.\"
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.Sh DESCRIPTION
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The
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.Fn getipnodebyname
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and
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.Fn getipnodebyaddr
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functions are very similar to
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.Xr gethostbyname 3 ,
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.Xr gethostbyname2 3
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and
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.Xr gethostbyaddr 3 .
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The functions cover all the functionalities provided by the older ones,
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and provide better interface to programmers.
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The functions require additional arguments,
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.Fa af ,
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and
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.Fa flags ,
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for specifying address family and operation mode.
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The additional arguments allow programmer to get address for a nodename,
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for specific address family
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(such as
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.Dv AF_INET
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or
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.Dv AF_INET6 ) .
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The functions also require an additional pointer argument,
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.Fa error_num
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to return the appropriate error code,
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to support thread safe error code returns.
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.Pp
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The type and usage of the return value,
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.Li "struct hostent"
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is described in
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.Xr gethostbyname 3 .
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.Pp
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For
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.Fn getipnodebyname ,
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the
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.Fa name
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argument can be either a node name or a numeric address
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string
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(i.e., a dotted-decimal IPv4 address or an IPv6 hex address).
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The
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.Fa af
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argument specifies the address family, either
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.Dv AF_INET
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or
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.Dv AF_INET6 .
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The
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.Fa flags
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argument specifies the types of addresses that are searched for,
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and the types of addresses that are returned.
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We note that a special flags value of
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.Dv AI_DEFAULT
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(defined below)
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should handle most applications.
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That is, porting simple applications to use IPv6 replaces the call
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.Bd -literal -offset
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hptr = gethostbyname(name);
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.Ed
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.Pp
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with
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.Bd -literal -offset
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hptr = getipnodebyname(name, AF_INET6, AI_DEFAULT, &error_num);
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.Ed
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.Pp
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Applications desiring finer control over the types of addresses
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searched for and returned, can specify other combinations of the
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.Fa flags
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argument.
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.Pp
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A
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.Fa flags
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of
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.Li 0
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implies a strict interpretation of the
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.Fa af
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argument:
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.Bl -bullet
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.It
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If
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.Fa flags
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is 0 and
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.Fa af
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is
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.Dv AF_INET ,
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then the caller wants only IPv4 addresses.
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A query is made for
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.Li A
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records.
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If successful, the IPv4 addresses are returned and the
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.Li h_length
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member of the
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.Li hostent
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structure will be 4, else the function returns a
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.Dv NULL
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pointer.
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.It
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If
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.Fa flags
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is 0 and if
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.Fa af
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is
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.Li AF_INET6 ,
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then the caller wants only IPv6 addresses.
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A query is made for
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.Li AAAA
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records.
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If successful, the IPv6 addresses are returned and the
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.Li h_length
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member of the
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.Li hostent
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structure will be 16, else the function returns a
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.Dv NULL
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pointer.
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.El
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.Pp
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Other constants can be logically-ORed into the
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.Fa flags
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argument, to modify the behavior of the function.
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.Bl -bullet
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.It
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If the
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.Dv AI_V4MAPPED
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flag is specified along with an
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.Fa af
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of
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.Dv AF_INET6 ,
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then the caller will accept IPv4-mapped IPv6 addresses.
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That is, if no
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.Li AAAA
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records are found then a query is made for
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.Li A
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records and any found are returned as IPv4-mapped IPv6 addresses
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.Li ( h_length
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will be 16).
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The
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.Dv AI_V4MAPPED
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flag is ignored unless
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.Fa af
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equals
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.Dv AF_INET6 .
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.It
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The
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.Dv AI_V4MAPPED_CFG
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flag is exact same as the
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.Dv AI_V4MAPPED
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flag only if the kernel supports IPv4-mapped IPv6 address.
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.It
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If the
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.Dv AI_ALL
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flag is used in conjunction with the
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.Dv AI_V4MAPPED
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flag, and only used with the IPv6 address family.
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When
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.Dv AI_ALL
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is logically or'd with
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.Dv AI_V4MAPPED
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flag then the caller wants all addresses: IPv6 and IPv4-mapped IPv6.
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A query is first made for
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.Li AAAA
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records and if successful, the
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IPv6 addresses are returned.
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Another query is then made for
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.Li A
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records and any found are returned as IPv4-mapped IPv6 addresses.
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.Li h_length
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will be 16.
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Only if both queries fail does the function
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return a
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.Dv NULL
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pointer.
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This flag is ignored unless af equals
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AF_INET6.
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If both
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.Dv AI_ALL
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and
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.Dv AI_V4MAPPED
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are specified,
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.Dv AI_ALL
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takes precedence.
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.It
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The
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.Dv AI_ADDRCONFIG
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flag specifies that a query for
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.Li AAAA
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records
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should occur only if the node has at least one IPv6 source
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address configured and a query for
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.Li A
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records should occur only if the node has at least one IPv4 source address
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configured.
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.Pp
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For example, if the node has no IPv6 source addresses configured,
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and
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.Fa af
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equals AF_INET6, and the node name being looked up has both
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.Li AAAA
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and
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.Li A
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records, then:
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(a) if only
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.Dv AI_ADDRCONFIG
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is
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specified, the function returns a
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.Dv NULL
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pointer;
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(b) if
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.Dv AI_ADDRCONFIG
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.Dv AI_V4MAPPED
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is specified, the
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.Li A
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records are returned as IPv4-mapped IPv6 addresses;
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.El
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.Pp
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The special flags value of
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.Dv AI_DEFAULT
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is defined as
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.Bd -literal -offset
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#define AI_DEFAULT (AI_V4MAPPED_CFG | AI_ADDRCONFIG)
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.Ed
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.Pp
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We noted that the
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.Fn getipnodebyname
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function must allow the
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.Fa name
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argument to be either a node name or a literal address string
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(i.e., a dotted-decimal IPv4 address or an IPv6 hex address).
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This saves applications from having to call
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.Xr inet_pton 3
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to handle literal address strings.
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When the
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.Fa name
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argument is a literal address string,
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the
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.Fa flags
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argument is always ignored.
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.Pp
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There are four scenarios based on the type of literal address string
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and the value of the
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.Fa af
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argument.
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The two simple cases are when
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.Fa name
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is a dotted-decimal IPv4 address and
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.Fa af
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equals
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.Dv AF_INET ,
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or when
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.Fa name
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is an IPv6 hex address and
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.Fa af
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equals
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.Dv AF_INET6 .
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The members of the
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returned hostent structure are:
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.Li h_name
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points to a copy of the
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.Fa name
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argument,
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.Li h_aliases
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is a
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.Dv NULL
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pointer,
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.Li h_addrtype
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is a copy of the
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.Fa af
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argument,
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.Li h_length
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is either 4
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(for
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.Dv AF_INET )
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or 16
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(for
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.Dv AF_INET6 ) ,
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.Li h_addr_list[0]
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is a pointer to the 4-byte or 16-byte binary address,
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and
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.Li h_addr_list[1]
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is a
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.Dv NULL
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pointer.
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.Pp
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When
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.Fa name
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is a dotted-decimal IPv4 address and
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.Fa af
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equals
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.Dv AF_INET6 ,
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and
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.Dv AI_V4MAPPED
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is specified,
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an IPv4-mapped IPv6 address is returned:
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.Li h_name
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points to an IPv6 hex address containing the IPv4-mapped IPv6 address,
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.Li h_aliases
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is a
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.Dv NULL
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pointer,
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.Li h_addrtype
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is
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.Dv AF_INET6 ,
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.Li h_length
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is 16,
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.Li h_addr_list[0]
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is a pointer to the 16-byte binary address, and
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.Li h_addr_list[1]
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is a
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.Dv NULL
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pointer.
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.Pp
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It is an error when
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.Fa name
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is an IPv6 hex address and
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.Fa af
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equals
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.Dv AF_INET .
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The function's return value is a
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.Dv NULL
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pointer and the value pointed to by
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.Fa error_num
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equals
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.Dv HOST_NOT_FOUND .
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.Pp
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The
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.Fn getipnodebyaddr
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function
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takes almost the same argument as
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.Xr gethostbyaddr 3 ,
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but adds a pointer to return an error number.
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Additionally it takes care of IPv4-mapped IPv6 addresses,
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and IPv4-compatible IPv6 addresses.
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.Pp
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The
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.Fn getipnodebyname
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and
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.Fn getipnodebyaddr
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functions
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dynamically allocate the structure to be returned to the caller.
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The
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.Fn freehostent
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function
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reclaims memory region allocated and returned by
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.Fn getipnodebyname
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or
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.Fn getipnodebyaddr .
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.\"
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.Sh FILES
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.Bl -tag -width /etc/nsswitch.conf -compact
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.It Pa /etc/hosts
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.It Pa /etc/nsswitch.conf
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.It Pa /etc/resolv.conf
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.El
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.\"
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.Sh DIAGNOSTICS
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The
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.Fn getipnodebyname
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and
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.Fn getipnodebyaddr
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functions
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returns
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.Dv NULL
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on errors.
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The integer values pointed to by
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.Fa error_num
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may then be checked to see whether this is a temporary failure
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or an invalid or unknown host.
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The meanings of each error code are described in
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.Xr gethostbyname 3 .
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.\"
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.Sh SEE ALSO
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.Xr getaddrinfo 3 ,
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.Xr gethostbyaddr 3 ,
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.Xr gethostbyname 3 ,
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.Xr getnameinfo 3 ,
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.Xr hosts 5 ,
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.Xr nsswitch.conf 5 ,
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.Xr services 5 ,
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.Xr hostname 7 ,
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.Xr named 8
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.Pp
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.Rs
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.%A R. Gilligan
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.%A S. Thomson
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.%A J. Bound
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.%A W. Stevens
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.%T Basic Socket Interface Extensions for IPv6
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.%R RFC2553
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.%D March 1999
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.Re
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.\"
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.Sh STANDARDS
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The
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.Fn getipnodebyname
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and
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.Fn getipnodebyaddr
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functions
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are documented in
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.Dq Basic Socket Interface Extensions for IPv6
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(RFC2553).
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.\"
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.Sh HISTORY
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The implementation first appeared in KAME advanced networking kit.
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.\"
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.Sh BUGS
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The
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.Fn getipnodebyname
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and
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.Fn getipnodebyaddr
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functions
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do not handle scoped IPv6 address properly.
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If you use these functions,
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your program will not be able to handle scoped IPv6 addresses.
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For IPv6 address manipulation,
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.Fn getaddrinfo 3
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and
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.Fn getnameinfo 3
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are recommended.
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.Pp
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The text was shamelessly copied from RFC2553.
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