Ping— This utility is an extremely useful diagnostic tool that initiates a simple test of network connectivity and reports on whether the other computer responds.
Configuration information utilities— Each OS vendor provides some form of utility that displays TCP/IP configuration information and lets you check whether the IP address, subnet mask, DNS server, and other parameters are configured properly.
arp— This lets you view and configure the contents of the ARP cache, which associates IP addresses with physical/MAC addresses.