November 2, 1997 ETHERS 3

### NAME

ether_ntoa, ether_aton, ether_ntohost, ether_hostton, ether_line, - get ethers entry

### LIBRARY

Standard C Library (libc, -lc)

### SYNOPSIS

```char``*` ether_ntoa(```const struct ether_addr *e`)
```struct` `ether_addr``*` ether_aton(```const char *s`)
```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 *line``, struct ether_addr *e``, char *hostname`)

### DESCRIPTION

Ethernet addresses are represented by the following structure:

  `

      struct ether_addr {
              u_char  ether_addr_octet[6];
      };

  `

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(``) 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.

The ether_ntohost(``) and ether_hostton(``) functions interrogate the data base 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. 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; if a + appears alone on a line in the file, then ether_hostton(``) will consult the ```ethers.byname` YP map, and ether_ntohost(``) will consult the ```ethers.byaddr` YP map.

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 ```hostname` buffer for ether_line(``) and ether_ntohost(``) should be at least ```MAXHOSTNAMELEN` + 1 characters long, to prevent a buffer overflow during parsing.

### 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 NetBSD1.0.

### 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.