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.\" Copyright (c) 1995

.\"     Bill Paul .  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 

.Fd #include 

.Fd #include 

.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 .