Gratuitous ARPs whenever you need them

Today I cloned a VM which had several IPs bounded to eth0. When I brought up the clone eth0 answered pings from my workstation (which is on a different network), but eth0:1, eth0:2, .. eth0:N did not. virt-clone had changed the MAC address as expected but why would a mac address change cause this problem? Turns out that the router between my workstation and dom0 had the old MAC address in its ARP cache and the ARP cache timeout is set high enough that I'd have to wait for it in order to reach the other IPs. But why wouldn't eth0 also be affected? Apparently when you boot a server it sends a Gratuitous ARP for eth0 but not eth0:1 etc. So the ARP cache for eth0 was updated but not the other IPs bound to eth0. What I wanted was to send a Gratuitous ARP for every IP bound to eth0 so that the cache would be refreshed. This is where arping is useful. E.g. to send a gratuitous ARP for the IP 192.168.6.212 whose gateway is 192.168.6.1, run:

/sbin/arping -s 192.168.6.212 -I eth0 192.168.6.1

From there it was just a matter of using a bash loop:

for x in `ifconfig | grep 192 | awk {'print $2'} | sed s/addr://g`; 
  do /sbin/arping -c 1 -s $x -I eth0 192.168.6.1 ;
done

I'm lucky my co-workers were able to help me understand this problem.