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Copyright 1989 AT&T.
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ethers, ether_ntoa, ether_ntoa_r, ether_aton, ether_aton_r, ether_ntohost, ether_hostton, ether_line - Ethernet address mapping operations

cc [ flag ... ] file ... -lsocket  -lnsl  [ library ... ]
#include <sys/types.h>
#include <sys/ethernet.h>

char *ether_ntoa(const struct ether_addr *e);

char *ether_ntoa_r(const struct ether_addr *e, char *s);

struct ether_addr *ether_aton(const char *s);

struct ether_addr *ether_aton_r(const char *s, struct ether_addr *e);

int ether_ntohost(char *hostname, const struct ether_addr *e);

int ether_hostton(const char *hostname, struct ether_addr *e);

int ether_line(const char *l, struct ether_addr *e, char *hostname);

These routines are useful for mapping 48 bit Ethernet numbers to their ASCII representations or their corresponding host names, and vice versa.

The function ether_ntoa() converts a 48 bit Ethernet number pointed to by e to its standard ASCII representation; it returns a pointer to the ASCII string. The representation is of the form x\|:\|x\|:\|x\|:\| x\|:\|x\|:\|x where x is a hexadecimal number between 0 and ff. The function ether_aton() converts an ASCII string in the standard representation back to a 48 bit Ethernet number; the function returns NULL if the string cannot be scanned successfully.

The functions ether_ntoa() and ether_aton() return values in per-thread buffers, one for each function. A second call to one of these functions will overwrite the previous value. The functions ether_ntoa_r() and ether_aton_r() behave identically to their non-reentrant versions; however, instead of using a per-thread buffer, they use caller supplied buffers. It is the callers responsibility to ensure that the character buffer passed to ether_ntoa_r() is at least ETHERADDRSTRL bytes large -- the minimum size to hold the ASCII representation of a 48 bit Ethernet number and a null terminator.

The function ether_ntohost() maps an Ethernet number (pointed to by e) to its associated hostname. The string pointed to by hostname must be long enough to hold the hostname and a NULL character. The function returns zero upon success and non-zero upon failure. Inversely, the function ether_hostton() maps a hostname string to its corresponding Ethernet number; the function modifies the Ethernet number pointed to by e. The function also returns zero upon success and non-zero upon failure. In order to do the mapping, both these functions may lookup one or more of the following sources: the ethers file and the NIS maps ethers.byname and ethers.byaddr. The sources and their lookup order are specified in the /etc/nsswitch.conf file. See nsswitch.conf(5) for details.

The function ether_line() scans a line, pointed to by l, and sets the hostname and the Ethernet number, pointed to by e. The string pointed to by hostname must be long enough to hold the hostname and a NULL character. The function returns zero upon success and non-zero upon failure. The format of the scanned line is described by ethers(5).

/etc/ethers /etc/nsswitch.conf

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE ATTRIBUTE VALUE

MT-Level MT-Safe

ethers (5), nsswitch.conf (5), attributes (7)