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.\" Copyright (c) 1995
.\"     Bill Paul <wpaul@ctr.columbia.edu>.  All rights reserved.
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.\"     $Id: ethers.3,v 1.2 2001-09-27 12:01:53 chris Exp $
.\"
.Dd April 12, 1995
.Dt ETHERS 3
.Os FreeBSD 2.1
.Sh NAME
.Nm ethers ,
.Nm ether_line ,
.Nm ether_aton ,
.Nm ether_ntoa ,
.Nm ether_ntohost ,
.Nm ether_hostton
.Nd Ethernet address conversion and lookup routines
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/socket.h>
.Fd #include <net/ethernet.h>
.Ft int
.Fn ether_line "char *l" "struct ether_addr *e" "char *hostname"
.Ft struct ether_addr *
.Fn ether_aton "char *a"
.Ft char *
.Fn ether_ntoa "struct ether_addr *n"
.Ft int
.Fn ether_ntohost "char *hostname" "struct ether_addr *e"
.Ft int
.Fn ether_hostton "char *hostname" "struct ether_addr *e"
.Sh DESCRIPTION
These functions operate on ethernet addresses using an
.Ar ether_addr
structure, which is defined in the header file
.Aq Pa netinet/if_ether.h :
.Bd -literal -offset indent
/*
 * The number of bytes in an ethernet (MAC) address.
 */
#define ETHER_ADDR_LEN          6

/*
 * Structure of a 48-bit Ethernet address.
 */
struct  ether_addr {
        u_char octet[ETHER_ADDR_LEN];
};
.Ed
.Pp
The function
.Fn ether_line
scans
.Ar l ,
an
.Tn ASCII
string in
.Xr ethers 5
format and sets
.Ar e
to the ethernet address specified in the string and
.Ar h
to the hostname. This function is used to parse lines from
.Pa /etc/ethers
into their component parts.
.Pp
The
.Fn ether_aton
function converts an
.Tn ASCII
representation of an ethernet address into an
.Ar ether_addr
structure. Likewise,
.Fn ether_ntoa
converts an ethernet address specified as an
.Ar ether_addr
structure into an
.Tn ASCII
string.
.Pp
The
.Fn ether_ntohost
and
.Fn ether_hostton
functions map ethernet addresses to their corresponding hostnames
as specified in the
.Pa /etc/ethers
database. 
.Fn ether_ntohost
converts from ethernet address to hostname, and
.Fn ether_hostton
converts from hostname to ethernet address.
.Sh RETURN VALUES
.Fn ether_line
returns zero on success and non-zero if it was unable to parse
any part of the supplied line
.Ar l .
It returns the extracted ethernet address in the supplied
.Ar ether_addr
structure
.Ar e
and the hostname in the supplied string
.Ar h .
.Pp
On success, 
.Fn ether_ntoa
returns a pointer to a string containing an
.Tn ASCII
representation of an ethernet address. If it is unable to convert
the supplied
.Ar ether_addr
structure, it returns a
.Dv NULL
pointer. Likewise,
.Fn ether_aton
returns a pointer to an
.Ar ether_addr
structure on success and a
.Dv NULL
pointer on failure.
.Pp
The
.Fn ether_ntohost
and
.Fn ether_hostton
functions both return zero on success or non-zero if they were
unable to find a match in the
.Pa /etc/ethers
database.
.Sh NOTES
The user must insure that the hostname strings passed to the
the
.Fn ether_line ,
.Fn ether_ntohost
and
.Fn ether_hostton
functions are large enough to contain the returned hostnames.
.Sh NIS INTERACTION
If the
.Pa /etc/ethers
contains a line with a single + in it, the
.Fn ether_ntohost
and
.Fn ether_hostton
functions will attempt to consult the NIS
.Pa ethers.byname
and
.Pa ethers.byaddr
maps in addition to the data in the
.Pa /etc/ethers
file.
.Sh SEE ALSO
.Xr yp 4 ,
.Xr ethers 5
.Sh BUGS
.Pp
The
.Fn ether_aton
and
.Fn ether_ntoa
functions returns values that are stored in static memory areas
which may be overwritten the next time they are called.
.Sh HISTORY
This particular implementation of the
.Nm ethers
library functions were written for and first appeared in
.Fx 2.1 .