.\"	$OpenBSD: inet_lnaof.3,v 1.4 2019/08/30 20:06:07 jmc Exp $
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.\"     @(#)inet.3	8.1 (Berkeley) 6/4/93
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.Dd $Mdocdate: August 30 2019 $
.Dt INET_LNAOF 3
.Os
.Sh NAME
.Nm inet_makeaddr ,
.Nm inet_netof ,
.Nm inet_lnaof
.Nd routines for manipulating classful Internet Protocol version 4 (IPv4) addresses
.Sh SYNOPSIS
.In arpa/inet.h
.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_lnaof "struct in_addr in"
.Sh DESCRIPTION
As originally designed,
IP version 4 split each address into a network part and local network
address part, encoding that split into the address itself.
It is frequency-encoded;
the most-significant bit is clear in Class A addresses,
in which the high-order 8 bits are the network number.
Class B addresses use the high-order 16 bits as the network field,
and Class C addresses have a 24-bit network part.
.Pp
The routine
.Fn inet_makeaddr
takes an Internet network number and a local
network address and constructs an Internet address
from it.
.Pp
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 SEE ALSO
.Xr gethostbyname 3 ,
.Xr inet_addr 3 ,
.Xr inet_net_ntop 3 ,
.Xr hosts 5
.Sh HISTORY
The
.Nm inet_makeaddr ,
.Nm inet_lnaof ,
and
.Nm inet_netof
functions appeared in
.Bx 4.2 .