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ETHERS(3)                BSD Library Functions Manual                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 <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 host-names hostnames
     names 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 host-name hostname
     name in the supplied string h.

     On success, ether_ntoa() returns a pointer to a string containing an ASCII representation of an ether-net ethernet
     net 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() func-tions functions
     tions will attempt to consult the NIS ethers.byname and ethers.byaddr maps in addition to the data in
     the /etc/ethers file.

SEE ALSO
     yp(4), ethers(5)

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.

BSD                             April 12, 1995                             BSD