4.3 ARP Cache

4.3 ARP Cache

Essential to the efficient operation of ARP is the maintenance of an ARP cache on each host. This cache maintains the recent mappings from Internet addresses to hardware addresses. The normal expiration time of an entry in the cache is 20 minutes from the time the entry was created.

We can examine the ARP cache with the arp (8) command. The -a option displays all entries in the cache:

 bsdi %  arp -a  sun (140.252.13.33) at 8:0:20:3:f6:42     svr4 (140.252.13.34) at 0:0:c0:c2:9b:26 

The 48-bit Ethernet addresses are displayed as six hexadecimal numbers separated by colons. We discuss additional features of the arp command in Section 4.8.