ETHERS(3) BSD Library Functions Manual ETHERS(3)NAME
ethers, ether_line, ether_aton, ether_aton_r, ether_ntoa, ether_ntoa_r,
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);
struct ether_addr *
ether_aton_r(const char *a, struct ether_addr *e);
char *
ether_ntoa(const struct ether_addr *n);
char *
ether_ntoa_r(const struct ether_addr *n, char *buf);
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 struc‐
ture, 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() and ether_aton_r() functions convert ASCII representa‐
tion of ethernet addresses into ether_addr structures. Likewise, the
ether_ntoa() and ether_ntoa_r() functions convert ethernet addresses
specified as ether_addr structures into ASCII strings.
The ether_ntohost() and ether_hostton() functions map ethernet addresses
to their corresponding hostnames as specified in the /etc/ethers data‐
base. The ether_ntohost() function converts from ethernet address to
hostname, and ether_hostton() converts from hostname to ethernet 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 structure e and the
hostname in the supplied string h.
On success, ether_ntoa() and ether_ntoa_r() functions return 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. ether_ntoa() stores the result in a static buffer;
ether_ntoa_r() stores the result in a user-passed buffer.
Likewise, ether_aton() and ether_aton_r() return a pointer to an
ether_addr structure on success and a NULL pointer on failure.
ether_aton() stores the result in a static buffer; ether_aton_r() stores
the result in a user-passed buffer.
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 ALSOethers(5), yp(8)HISTORY
This particular implementation of the ethers library functions were writ‐
ten for and first appeared in FreeBSD 2.1. Thread-safe function variants
first appeared in FreeBSD 7.0.
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.
ether_ntoa_r() accepts a character buffer pointer, but not a buffer
length. The caller must ensure adequate space is available in the buffer
in order to avoid a buffer overflow.
BSD October 30, 2007 BSD
