ETHERS(3)

NAME
ethers, ether_line, ether_aton, ether_ntoa, ether_ntohost, ether_hostton - Ethernet address conversion and lookup routines

LIBRARY
libc

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
ethers(5), yp(8)

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.