Problem: When you run “show arp” on an edge router/firewall you see thousands of public IPs. This will eat up the memory and cause things to run slowly. I even saw in once case where “show run” revealed nothing, it would just come back blank because there wasn’t any memory available to perform the command.
Solution: Chances are the default route is using an interface as a destination and not an IP. Such as
ip route 0.0.0.0 0.0.0.0 Gig0/0
Change this to use an IP address and not an interface. If an interface is used then there is no MAC that can be used as a destination and so the router sends an ARP request for the destination IP and adds it to the local table.