CMD (run as admin)

netstat -an
Display all open ports on the current device
youtube explanation here

ping /t
Ping a specific address to determine that there is a good connection. The /t is for endless ping.

Trace the route from your device to the selected IP. It will bring up a list of all the routers the ping is passing to reach the end IP.
Youtube explanation here

Is tracing the route to the end IP, with a specification of the delay on each router.
Youtube explanation here

Show the status on all your netcards.

add /release to release all ip adresses on your system

add /renew to pull new adresses from the DHCP servers.

add /flushdns to clean up your dns buffer. 
youtube explanation here