Netstat Networking Utility
The netstat networking utility shows network statistics for the networking interfaces on the computer you are using. This command can be infinitely useful if you’re having a problem connecting to a certain resource – you will be able to see the current status of the connection and what port it is connecting on.
Here are the different options you can use with netstat:
H:\>netstat /? Displays protocol statistics and current TCP/IP network connections. NETSTAT [-a] [-b] [-e] [-n] [-o] [-p proto] [-r] [-s] [-v] [interval] -a Displays all connections and listening ports. -b Displays the executable involved in creating each connection or listening port. In some cases well-known executables host multiple independent components, and in these cases the sequence of components involved in creating the connection or listening port is displayed. In this case the executable name is in  at the bottom, on top is the component it called, and so forth until TCP/IP was reached. Note that this option can be time-consuming and will fail unless you have sufficient permissions. -e Displays Ethernet statistics. This may be combined with the -s option. -n Displays addresses and port numbers in numerical form. -o Displays the owning process ID associated with each connection. -p proto Shows connections for the protocol specified by proto; proto may be any of: TCP, UDP, TCPv6, or UDPv6. If used with the -s option to display per-protocol statistics, proto may be any of: IP, IPv6, ICMP, ICMPv6, TCP, TCPv6, UDP, or UDPv6. -r Displays the routing table. -s Displays per-protocol statistics. By default, statistics are shown for IP, IPv6, ICMP, ICMPv6, TCP, TCPv6, UDP, and UDPv6; the -p option may be used to specify a subset of the default. -v When used in conjunction with -b, will display sequence of components involved in creating the connection or listening port for all executables. interval Redisplays selected statistics, pausing interval seconds between each display. Press CTRL+C to stop redisplaying statistics. If omitted, netstat will print the current configuration information once.
In the real world, you will often use netstat to see what network connections are open on the network interface. The output from netstat shows the connection, what port you are connected to (e.g. 1434 or http), and the status of the connection.