The ethers database contains information regarding known 48-bit ethernet addresses of hosts on an Internetwork. The data is stored in a file called /etc/ethers in the following format:
Items are separated by any number of blanks and/or tab characters. A # at the start of a line indicates the beginning of a comment that extends to the end of the line. A + at the start of a line will cause the ethers(3) library functions to use data stored in the NIS ethers.byname and ethers.byaddr maps in addition to the data in the /etc/ethers file.
An ethernet address is expressed in ASCII form as "x:x:x:x:x:x" where x is a hexadecimal value between 0x00 and 0xFF. The address values should be in network order. Hostnames specified in the /etc/ethers database should correspond to entries in the hosts(5) file.
The ether_line function in the standard C library can be used to break individual lines in the /etc/ethers database into their individual components: a binary Ethernet address stored as an ether_addr structure, and a hostname stored as a character string.