HowTo: Linux Send a Gratuitous ARPs Requests

How do I send gratuitous ARPs under Linux? How do I tell my DUMMY router that the IP is over here now, under Linux operating systems?

You can use the arping command to send a gratuitous reply using the -A option. arping can send ARP REQUEST to a neighbor host:
# arping -U {IP-HERE} -I {Interface-Name-HERE}
# arping -A -c {Number} -I {Interface-Name-HERE}
# arping -U 1.2.3.4 -I eth1
The following command will send a Gratuitous ARP reply, four times, on the eth1 interface for IP address 1.2.3.4.
# arping -c 4 -A -I eth1 1.2.3.4

Where,

1. -A : ARP reply
2. -C 4: Send it four times
3. -I eth1: Use eth1 interface
4. 1.2.3.4: Replace this with your actual IP address.

轉自：http://www.cyberciti.biz/faq/linux-networking-sending-gratuitous-arps/