ethers(3)

NAME

ethers, ether_line, ether_aton, ether_ntoa, ether_ntohost,

ether_hostton
- Ethernet address conversion and lookup routines

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <sys/types.h>
#include <sys/socket.h>
#include <net/ethernet.h>
int
ether_line(const   char   *l,  struct  ether_addr  *e,  char
*hostname);
struct ether_addr *
ether_aton(const char *a);
char *
ether_ntoa(const struct ether_addr *n);
int
ether_ntohost(char *hostname, const struct ether_addr *e);
int
ether_hostton(const char *hostname, struct ether_addr *e);

DESCRIPTION

These functions operate on ethernet addresses using an

ether_addr structure, which is defined in the header file

/*

* 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];

};

The function ether_line() scans l, an ASCII string in

ethers(5) format
and sets e to the ethernet address specified in the string

and h to the
hostname. This function is used to parse lines from

/etc/ethers into
their component parts.

The ether_aton() function converts an ASCII representation

of an ethernet
address into an ether_addr structure. Likewise,

ether_ntoa() converts an
ethernet address specified as an ether_addr structure into

an ASCII
string.

The ether_ntohost() and ether_hostton() functions map ether

net addresses
to their corresponding hostnames as specified in the

/etc/ethers
database. The ether_ntohost() function converts from ether

net address to
hostname, and ether_hostton() converts from hostname to eth

ernet address.

RETURN VALUES

The ether_line() function returns zero on success and non

zero if it was
unable to parse any part of the supplied line l. It returns

the
extracted ethernet address in the supplied ether_addr struc

ture e and the
hostname in the supplied string h.

On success, ether_ntoa() returns a pointer to a string con

taining an
ASCII representation of an ethernet address. If it is un

able to convert
the supplied ether_addr structure, it returns a NULL point

er. Likewise,
ether_aton() returns a pointer to an ether_addr structure on

success and
a NULL pointer on failure.

The ether_ntohost() and ether_hostton() functions both re

turn zero on
success or non-zero if they were unable to find a match in

the
/etc/ethers database.

NOTES

The user must insure that the hostname strings passed to the
ether_line(), ether_ntohost() and ether_hostton() functions

are large
enough to contain the returned hostnames.

NIS INTERACTION

If the /etc/ethers contains a line with a single + in it,

the
ether_ntohost() and ether_hostton() functions will attempt

to consult the
NIS ethers.byname and ethers.byaddr maps in addition to the

data in the
/etc/ethers file.

SEE ALSO

ethers(5), yp(8)

HISTORY

This particular implementation of the ethers library func

tions were written for and first appeared in FreeBSD 2.1.

BUGS

The ether_aton() and ether_ntoa() functions returns values

that are
stored in static memory areas which may be overwritten the

next time they
are called.

BSD April 12, 1995

BSD