ARP Cache

The ARP cache is a table which stores mappings between Data Link Layer addresses and Network Layer addresses.

The Data Link Layer addresses are usually MAC addresses and the Network Layer addresses are most frequently IP addresses.

The ARP cache is stored in RAM by the Operating System.

Displaying the ARP cache

Under most versions of Unix and Microsoft Windows, the command `arp -a` will display the ARP cache.

Unix ARP Cache Example

$ arp -a
www.tech-faq.com (192.168.1.2) at 00:34:c4:45:73:21 on fxp0 permanent [ethernet]
fw.tech-faq.com (192.168.1.1) at 00:34:62:a1:c2:00 on fxp0 [ethernet]

Microsoft Windows ARP Cache Example

C:\>arp -a

Interface: 192.168.1.101 --- 0x80004
Internet Address Physical Address Type
192.168.1.1 00-0d-6d-bc-a8-6b dynamic
192.168.1.2 00-0e-1c-2b-e5-3c dynamic

Further Reading on the ARP Cache

To learn more about the ARP protocol, read What is ARP?

To learn how to clear the ARP cache, read How do I clear the ARP cache?