ETHER_ATON(3) | Library Functions Manual | ETHER_ATON(3)

# NAME

`ether_aton`, `ether_ntoa`, `ether_ntohost`, `ether_hostton`, `ether_line` — get ethers entry

# SYNOPSIS

`#include <sys/types.h>`
`#include <sys/socket.h>`
`#include <net/if.h>`
`#include <netinet/in.h>`
`#include <netinet/if_ether.h>`

char *
`ether_ntoa`(const struct ether_addr *e);

struct ether_addr *
`ether_aton`(const char *s);

int
`ether_ntohost`(char *hostname, 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);

# DESCRIPTION

Ethernet addresses are represented by the following structure:

    struct ether_addr {
            u_int8_t  ether_addr_octet[ETHER_ADDR_LEN];
    };

The `ether_ntoa`() function converts this structure into an ASCII string of the form “xx:xx:xx:xx:xx:xx”, consisting of 6 hexadecimal numbers separated by colons. It returns a pointer to a static buffer that is reused for each call. The `ether_aton`() function converts an ASCII string of the same form and to a structure containing the 6 octets of the address. It returns a pointer to a static structure that is reused for each call. `ether_aton`() will return NULL if the string does not represent a valid address.

The `ether_ntohost`() and `ether_hostton`() functions interrogate the database mapping host names to Ethernet addresses, /etc/ethers. The `ether_ntohost`() function looks up the given Ethernet address and writes the associated host name into the character buffer passed. This buffer should be `MAXHOSTNAMELEN` characters in size. The `ether_hostton`() function looks up the given host name and writes the associated Ethernet address into the structure passed. Both functions return zero if they find the requested host name or address, and -1 if not.

Each call reads /etc/ethers from the beginning.

The `ether_line`() function parses a line from the /etc/ethers file and fills in the passed struct ether_addr and character buffer with the Ethernet address and host name on the line. It returns zero if the line was successfully parsed and -1 if not. The character buffer should be `MAXHOSTNAMELEN` characters in size.

# FILES

/etc/ethers

# SEE ALSO

ethers(5)

# HISTORY

The `ether_ntoa`(), `ether_aton`(), `ether_ntohost`(), `ether_hostton`(), and `ether_line`() functions were adopted from SunOS and appeared in NetBSD 0.9B.

# BUGS

The data space used by these functions is static; if future use requires the data, it should be copied before any subsequent calls to these functions overwrite it.

June 29, 2025 | Debian