Occasionally when you are migrating virtual machines (when using Vmware, Hyper-V, XEN, etc.) in a datacenter enviornment a router can get stuck with old ARP entries.  Removing and republishing the route can do this for you, however the fastest way from a Linux server to clear old ARP entries is arping if you do not have direct access to the routers or do not want to contact support. Generally, running a arping from the affect ip address will remove the old entry and reannounce ARP properly.  Below is a example command to remove a bad ARP entry:

arping 100.37.111.161 -I eth1 -s 100.37.111.166

In the above example command, the first address would be the network gateway, the  -I syntax indicates the interface used, and the -s would be the affected ip address that contains old ARP entries.