Router stops responding / sending traffic due to ARP

Cisco Router stops sending / Recieving traffic despite of interfaces being in  up/up state ???

First things first, check if the routing protocols,NAT and ACL are properly configured.
Ping to Default Gateway, if it is pinging properly then check if the configurations are correct and still router is not sending /receiving traffic then ARP could be flooded !

Cisco uses default arp  timeout as 14400 but some time it gets flushed

First to be sure if this is the scenario, check

                                           Router<Config># sh cpu process history

If ARP is getting flooded then the first or second most used process will be for ARP.check for memory as well as shown in below pic

Router#Show proc mem sorted

If the memory is getting completely utilized and ARP is the most used process then you need to flush the ARP records manually. you can do this using the below command.

Router<Config># arp timeout 14400

This command is used to refresh ARP after every 4 hours.