The arp command is useful for viewing the ARP cache. If two hosts on the same subnet cannot ping each other successfully, try running the arp -a command on each computer to see if the computers have the correct MAC addresses listed for each other. Use IPConfig to determine a host's media access control address. If another host with a duplicate IP address exists on the network, the ARP cache may have had the media access control address for the other computer placed in it. Use arp -d to delete an entry that may be incorrect. Add entries by using arp -s.