The ping command.
Ping is a useful TCP/IP utility to check network connectivity. Two other useful troubleshooting tools are Ipconfig (Windows 200/XP) and Winipcfg (Windows 9x/ME), which test TCP/IP configuration.
TCP IP utility was the most useful when troubleshooting for a few reasons. It contains important information like NetBIOS over TCP IP and there connections.
Use the 'netstat' utility
Novell NetWare, and TCP/IP networks
The TCP/IP utilities are used to troubleshoot and diagnose issues with TCP/IP protocols. Ping is used to test connectivity between nodes in a network, netstat will show you ports in use and network connections, traceroute will trace the hops between routers/networks, nslookup and dig can be used to troubleshoot DNS problems.
Novell NetWare, and TCP/IP networks
netstat--A TCP/IP troubleshooting utility that displays stats and the state of the current TCP/IP connections.
Use Ping to the local loopback adaptor; that tests whether TCP/IP has been installed and is working on the system.
Tracert
A group of utility tools is also installed that can troubleshoot problems with TCP/IP. (6th Edition, - Page 928).
rtye5yeye
I'm pretty sure that it's ifconfig...