The –a Switch

The –a Switch
When you use the –a switch, the netstat utility displays all TCP/IP connections and all User Datagram Protocol (UDP) connections. Figure 4.2 shows a sample output produced by the netstat –a command.
The last two entries in Figure 4.2 show a protocol type of UDP and the source port nicknames of nbname and nbdatagram, which are the well-known port numbers of 137 and 138, respectively. These port numbers are commonly seen on networks that broadcast the NetBIOS name of a workstation on the TCP/IP network. You can tell that this is a broadcast because the destination address is listed as *:* (meaning “any address, any port”).  

FIGURE 4 . 2 Sample output of the netstat –a command

NOTE:

The State column has no entry because UDP is not a connection-oriented protocol and, therefore, has no connection state.

The most common use for the –a switch is to check the status of a TCP/IP connection that appears to be hung. You can determine if the connection is simply busy or is actually hung and no longer responding.