Updating Router ARP Cache

During the ip migration or swapping one of the common issue the admin face with the Data Center(DC) is ARP caching on the router. The router is usually setup to clear the ARP cache after long hours. So we may need to contact the Data center network admin to clear the arp cache or have to wait for until it clears itself. On heavy loaded web servers this down time may cause money loss. We can use arping or send_arp tools to update the roter ARP cache from the new server.


For example if your swapped ip address is , login in to the new server and execute the arping with the following syntax.


  • # arping -U -I eth0


-UUnsolicited ARP mode.
-I — Your ethernet interface.


Using send_arp to release ARP Cache


If you are on cluster environment using the send_arp command is the best way.


  • # send_arp [-i dev] src_ip_addr src_hw_addr targ_ip_addr tar_hw_addr
  • #  send_arp -i eth0 <old_server_mac-add> <new_server_mac-add>


Wait for few minutes and try pinging or access the ip address from your location.