What is the cause and remedy. And, how can I block pinging router from outside world?
Now coming to your problem, on which interface are you experiencing this – serial or Ethernet interface.
On serial interfaces you would find this when there is a sudden file transfers initiated by users. You should monitor to see if there is any unauthenticated use of your network than you can either use QOS mechanisms or access-list to block those users. You would see increased drops also.
On Ethernet interfaces you would see this type of loading when any machine is sending rapid broadcasts or (as in case of serial interface) there are huge file transfers. File transfers need to be tackled in same way. Causes of broadcasts could be a malfunctioning NIC, a broken cable or virus. You need to zero in on the machine that is sending the traffic, take it out of the network and rectify the problem.
This was first published in February 2004