Our internet router sometimes (5 to 20 minutes in a day) becomes unresponsive for the public interface of our VPN device 'nortel contivity'. When we look into the logs/alerts on router we found that at the time of outage the router requests arp for the contivity IP and mac address 'all zeros' 0000.0000.0000. We have configured the router for manual arp entry for contivity public ip, even than why does it request arp abnormally? This vpn outage occures for 5 to 20 minutes without any pattern i.e. sometimes quite frequently and sometimes once in a month or so. Surprisingly, recently the IP becomes responsive as soon as we use 'clear arp-cache' command at router. CEF is enabled by default. What do you think where is the problem existing?