The netstat command is used for displaying network connections, routing tables, interface statistics, masquerade connections, and multicast memberships on Unix-like operating systems. It provides valuable information about active TCP connections, UDP ports in use, listening ports, routing table entries, and network interface statistics. Netstat is crucial for network troubleshooting, monitoring network performance, and diagnosing connectivity issues.
To find IP addresses using netstat, you can use specific options depending on your operating system. On Unix-like systems, you can use netstat -rn to display the routing table, which includes IP addresses associated with network interfaces and routing entries. On Windows, netstat -r provides similar information. Alternatively, netstat -an displays all active connections and their associated IP addresses.
To use netstat to check connections on a specific port, you can specify the port number using the appropriate options. For example, on Unix-like systems, netstat -an | grep PORT_NUMBER will display active connections (both listening and established) on the specified port number. On Windows, netstat -an | find “PORT_NUMBER” achieves a similar result by filtering connections based on the specified port number.
To check active connections using the netstat command, you can use options such as -a to display all connections, -t for TCP connections, -u for UDP connections, and -n to show numerical addresses instead of resolving hostnames. For example, netstat -an will show all active connections with numerical addresses and ports. You can filter the output further using tools like grep on Unix-like systems or find on Windows to focus on specific connections or port numbers.
Using netstat in a shell script involves writing a script that includes the netstat command with desired options and possibly using other Unix utilities to process or manipulate the output. For example, a simple shell script might use netstat -an | grep “ESTABLISHED” to find established connections and perform further actions based on the results. Shell scripting with netstat allows automation of network monitoring tasks, generation of reports, or integration with other system management tasks.