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
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);
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 structure, which is defined in the header file <net/ethernet.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 representation 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 database. 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 ensure 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 functions were written 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.