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. -: 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.

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