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 ⟨netinet/if_ether.h⟩:
/*
* 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 ethernet addresses to their corresponding hostnames as
specified in the /etc/ethers database.
ether_ntohost() converts from ethernet address to
hostname, and ether_hostton() converts from hostname
to ethernet address.
RETURN VALUES
ether_line() 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 structure e
and the hostname in the supplied string h.
On success, ether_ntoa() returns a pointer
to a string containing an ASCII representation of an ethernet address. If it
is unable to convert the supplied ether_addr
structure, it returns a NULL pointer. 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 return 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
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.
HISTORY
This particular implementation of the
ethers library functions were written for and first
appeared in FreeBSD 2.1.