The flags field can contain such values as: U , which indicates that the network link is up H , which indicates that destination address refers to a host rather than a network G , which indicates that the routing rule specifies a gateway
To permanently add hostname 's Ethernet address to the ARP tables. The hwaddr argument specifies the hardware address, which is by default expected to be an Ethernet address specified as six hexadecimal bytes separated by colons.
arp -s hostname hwaddr
deletes all ARP entries relating to the given host. This switch may be used to force the interface to re-attempt obtaining the Ethernet address for the IP address in question. This is useful when a misconfigured system has broadcasted wrong ARP information (of course, you have to reconfigure the broken host first).