Man page 5 : ethers

ethers - Ethernet address to IP number database

/etc/ethers contains 48 bit Ethernet addresses and their corresponding IP numbers, one line for each IP number:

Ethernet-address IP-number

The two items are separated by any number of SPACE and/or TAB characters. A # at the beginning of a line starts a comment which extends to the end of the line. The Ethernet-address is written as x : x : x : x : x : x , where x is a hexadecimal number between 0 and ff which represents one byte of the address, which is in network byte order (big-endian). The IP-number may be a hostname which can be resolved by DNS or a dot separated number.

08:00:20:00:61:CA pal

/etc/ethers

rarp(8)