How can you manually add an entry to your system’s ARP cache?

A.
Directly edit /etc/arp-cache

B.
Run add-arp hostname FF:FF:FF:FF:FF:FF

C.
Run ping -a hostname

D.
Run arp -s hostname FF:FF:FF:FF:FF:FF

E.
Edit arp.conf and restart arpd

Explanation:
From the man pages:
-s hostname hw_addr, –set hostname
Manually create an ARP address mapping entry for host hostname with hardware address set to
hw_addr class, but for most classes one can assume that the usual presentation can be used. For the
Ethernet class, this is 6 bytes in hexadecimal, separated by colons. When adding proxy arp entries
(that is those with the publish flag set a netmask may be specified to proxy arp for entire subnets.
This is not good practice, but is supported by older kernels because it can be useful. If the temp flag
is not supplied entries will be permanent stored into the ARP cache.