Netstat Command
The netstat command, it can show details about individual network connections, overall and protocol-specific networking statistics, and much more, all of which could help troubleshoot certain kinds of networking issues.
Netstat Command Syntax
netstat [-a] [-b] [-e] [-f] [-n] [-o] [-p protocol] [-r] [-s] [-t] [-x] [-y] [time_interval] [/?]
How to Read Command Syntax
| Netstat Command List | |
|---|---|
| Option | Explanation |
| netstat | Execute the netstat command alone to show a relatively simple list of all active TCP connections, which, for each one, will show the local IP address (your computer), the foreign IP address (the other computer or network device), along with their respective port numbers, as well as the TCP state. |
| -a | This switch displays active TCP connections, TCP connections with the listening state, as well as UDP ports that are being listened to. |
| -b | This netstat switch is very similar to the -o switch listed below, but instead of displaying the PID, it will display the process’s actual file name. Using -b over -o might seem like it’s saving you a step or two but using it can sometimes greatly extend the time it takes netstat to fully execute. |
| -e | Use this switch with the netstat command to show statistics about your network connection. This data includes bytes, unicast packets, non-unicast packets, discards, errors, and unknown protocols received and sent since the connection was established. |
| -f | The -f switch will force the netstat command to display the Fully Qualified Domain Name (FQDN) for each foreign IP address when possible. |
| -n | Use the -n switch to prevent netstat from attempting to determine hostnames for foreign IP addresses. Depending on your current network connections, using this switch could considerably reduce the time it takes for netstat to fully execute. |
| -o | A handy option for many troubleshooting tasks, the -o switch displays the process identifier (PID) associated with each displayed connection. See the example below for more about using netstat -o. |
| -p | Use the -p switch to show connections or statistics only for a particular protocol. You can not define more than one protocol at once or execute netstat with -p without defining a protocol. |
| protocol | When specifying a protocol with the -p option, you can use tcp, udp, tcpv6, or udpv6. If you use -s with -p to view statistics by protocol, you can use icmp, ip, icmpv6, or ipv6 in addition to the first four I mentioned. |
| -r | Execute netstat with -r to show the IP routing table. This is the same as using the route command to execute route print. |
| -s | The -s option can be used with the netstat command to show detailed statistics by protocol. You can limit the statistics shown to a particular protocol by using the -soption and specifying that protocol, but be sure to use -s before -p protocol when using the switches together. |
| -t | Use the -t switch to show the current TCP chimney offload state instead of the typically displayed TCP state. |
| -x | Use the -x option to show all NetworkDirect listeners, connections, and shared endpoints. |
| -y | The -y switch can be used to show the TCP connection template for all connection. You cannot use -y with any other netstat option. |
| time_interval | This is the time, in seconds, that you’d like the netstat command to re-execute automatically, stopping only when you use Ctrl-C to end the loop. |
| /? | Use the help switch to show details about the netstat command’s several options. |
Make all that netstat information in the command line easier to work with by outputting what you see on the screen to a text file using a redirection operator. See How to Redirect Command Output to a File for complete instructions.
Netstat Command Examples
Here are several examples showing how the netstat command might be used:
Show Active TCP Connections
netstat -fIn this first example, we execute netstat to show all active TCP connections. However, we want to see the computers that we’re connected to in FQDN format [-f] instead of a simple IP address.
Here’s an example of what you might see:
Active ConnectionsProto Local Address Foreign Address StateTCP 127.0.0.1:5357 VM-Windows-7:49229 TIME_WAITTCP 127.0.0.1:49225 VM-Windows-7:12080 TIME_WAITTCP 192.168.1.14:49194 75.125.212.75:http CLOSE_WAITTCP 192.168.1.14:49196 a795sm.avast.com:http CLOSE_WAITTCP 192.168.1.14:49197 a795sm.avast.com:http CLOSE_WAITTCP 192.168.1.14:49230 TIM-PC:wsd TIME_WAITTCP 192.168.1.14:49231 TIM-PC:icslap ESTABLISHEDTCP 192.168.1.14:49232 TIM-PC:netbios-ssn TIME_WAITTCP 192.168.1.14:49233 TIM-PC:netbios-ssn TIME_WAITTCP [::1]:2869 VM-Windows-7:49226 ESTABLISHEDTCP [::1]:49226 VM-Windows-7:icslap ESTABLISHED
As you can see, there were 11 active TCP connections when netstat was executed in this example. The only protocol (in the Proto column) listed is TCP, which was expected because we didn’t use -a.
You can also see three sets of IP addresses in the Local Address column—the actual address of 192.168.1.14 and both IPv4 and IPv6 versions of the loopback addresses, along with the port each connection is using. The Foreign Address column lists the FQDN (75.125.212.75 didn’t resolve for some reason) along with that port as well.
Finally, the State column lists the TCP state of that particular connection.
Show Connections and Process Identifiers
netstat -oIn this example, netstat will be run normally so it only shows active TCP connections, but we also want to see the corresponding process identifier [-o] for each connection so that we can determine which program on the computer initiated each one.
Here’s what the computer displayed:
Active ConnectionsProto Local Address Foreign Address State PIDTCP 192.168.1.14:49194 75.125.212.75:http CLOSE_WAIT 2948TCP 192.168.1.14:49196 a795sm:http CLOSE_WAIT 2948TCP 192.168.1.14:49197 a795sm:http CLOSE_WAIT 2948
You probably noticed the new PID column. In this case, the PIDs are all the same, meaning the same program on the computer opened these connections.
To determine what program is represented by the PID of 2948 on the computer, open Task Manager to the Processes tab, and note the Image Name listed next to the PID we’re looking for in the PID column.1
Using the netstat command with the -o option can be very helpful when tracking down which program uses too big a share of your bandwidth. It can also help locate the destination where some kind of malware, or even an otherwise legitimate piece of software, might send information without your permission.
While this and the previous example were both run on the same computer and within just a minute of each other, you can see that the list of active TCP connections is considerably different. This is because your computer is constantly connecting to, and disconnecting from, various other devices on your network and over the internet.
Show Specific Connections Only
netstat -0 | findstr 28604The above example is similar to what we’ve already looked at, but instead of displaying all connections, we’re telling the command to show only the connections that are using a specific PID, 28604 in this example.
A similar command could be used to filter out the connections with a CLOSE_WAIT state, by replacing the PID with ESTABLISHED.
Show Protocol-Specific Stats
netstat -s -p tcp -fHere, we want to see protocol specific statistics [-s] but not all of them, just TCP stats [-p tcp]. We also want the foreign addresses displayed in FQDN format [-f].
This is what that netstat command produced for us:
TCP Statistics for IPv4Active Opens = 77Passive Opens = 21Failed Connection Attempts = 2Reset Connections = 25Current Connections = 5Segments Received = 7313Segments Sent = 4824Segments Retransmitted = 5Active ConnectionsProto Local Address Foreign Address StateTCP 127.0.0.1:2869 VM-Windows-7:49235 TIME_WAITTCP 127.0.0.1:2869 VM-Windows-7:49238 ESTABLISHEDTCP 127.0.0.1:49238 VM-Windows-7:icslap ESTABLISHEDTCP 192.168.1.14:49194 75.125.212.75:http CLOSE_WAITTCP 192.168.1.14:49196 a795sm.avast.com:http CLOSE_WAITTCP 192.168.1.14:49197 a795sm.avast.com:http CLOSE_WAIT
As you can see, various statistics for the TCP protocol are displayed, as are all active TCP connections at the time.
Show Updated Network Stats
netstat -e -t 5In this final example, netstat shows some basic network interface statistics [-e] that are continually updated in the command window every five seconds [-t 5].
Here’s what’s produced on screen:
Interface StatisticsReceived SentBytes 22132338 1846834Unicast packets 19113 9869Non-unicast packets 0 0Discards 0 0Errors 0 0Unknown protocols 0Interface StatisticsReceived SentBytes 22134630 1846834Unicast packets 19128 9869Non-unicast packets 0 0Discards 0 0Errors 0 0Unknown protocols 0^C
Various pieces of information, which you can see here and that we listed in the -e syntax above, are displayed.
The command only automatically executed one extra time, as shown by the two tables in the result. Note the ^C at the bottom, indicating that the Ctrl+C abort command was used to stop the re-running of the command.
Netstat Related Commands
The netstat command is often used with other networking related Command Prompt commands like nslookup, ping, tracert, ipconfig, and others.
[1] You might have to manually add the PID column to Task Manager. You can do this by selecting PID after right-clicking the column headings in the Process tab. If you’re using Windows 7 or on older Windows OS, select the PID (Process Identifier) checkbox from View > Select Columns in Task Manager. You might also have to choose Show processes from all users from the bottom of the Processes tab if the PID you’re looking for isn’t listed.
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