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ETHERS(3)	      DragonFly Library Functions Manual	     ETHERS(3)


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


Standard C Library (libc, -lc)


#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);


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.


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.


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.


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.


ethers(5), yp(8)


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.


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. DragonFly 4.7 October 30, 2007 DragonFly 4.7

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