How to use the command Test-NetConnection (with examples)

Test-NetConnection is a powerful and versatile command available in PowerShell that assists network administrators and users in diagnosing and troubleshooting network connection issues. It provides an array of diagnostic information about network connectivity, including the ability to ping remote devices, test specific TCP ports, and probe TraceRoute. This command is particularly useful for verifying the status of connections and ensuring that networks are performing as expected. Let’s explore these use cases in detail with examples.

Use case 1: Test a connection and display detailed results

Code:

Test-NetConnection -InformationLevel Detailed

Motivation: This use case is essential for users who want to gather comprehensive information about their network connection. By using the -InformationLevel Detailed parameter, users can acquire a deeper understanding of the connectivity status, which includes various metrics and data points. This is particularly useful when troubleshooting network issues that are not obvious, as the detailed output can provide insights into potential points of failure or areas where optimization may be required.

Explanation:

• Test-NetConnection: This is the primary command being executed, which prompts PowerShell to start a network diagnostic check.
• -InformationLevel: This parameter modifies the depth of information returned by the command.
• Detailed: This argument specifies that the output should include detailed diagnostic information. It enriches the typical network function analysis with in-depth details, such as the latency, response times, and the connection’s status, effectively supporting comprehensive diagnostics.

Example Output: When you run this command, you might receive an output similar to the following:

WARNING: Detailed Network Connection Test Results: 

InterfaceAlias       : Ethernet
InterfaceIndex       : 12
SourceAddress        : 192.168.1.5
NetRoute (NextHop)   : 192.168.1.1
PingSucceeded        : True
PingReplyDetails (RTT): 15ms
TcpTestSucceeded     : True
TraceRoute           :
Hop                  : 1, IP Address: 192.168.1.1, HostName: home.gateway, RTT: 10ms
Hop                  : 2, IP Address: 172.16.0.1, HostName: border.gateway, RTT: 20ms
...

This output reveals not just the success of a ping operation but also the entire path your packet takes with a trace route, the exact interfaces involved, and more.

Use case 2: Test a connection to a remote host using the specified port number

Code:

Test-NetConnection -ComputerName ip_or_hostname -Port port_number

Motivation: This particular use case is invaluable when verifying connectivity to a specific service running on a port on a remote machine. Often, network issues arise not from the inability to reach a machine but from blocked ports or services that are down. Network administrators and support staff use this command to confirm whether a TCP connection can be opened to a given port on a specified server, which is critical for diagnosing service connectivity issues such as blocked Firewalls, security group policies, or inactive services.

Explanation:

• Test-NetConnection: Initiates the network connectivity check.
• -ComputerName: This argument specifies the target device’s hostname or IP address. It directs the command to the network device with which you are testing connectivity.
• -Port: This argument denotes the specific port number you wish to test connectivity with on the target device. By providing this parameter, the command will attempt to open a TCP connection on that specified port, indicating whether or not access to that port is allowed and functioning.

Example Output: Once the command runs, you may receive an output resembling the following:

ComputerName     : www.example.com
RemoteAddress    : 93.184.216.34
RemotePort       : 80
InterfaceAlias   : Ethernet
SourceAddress    : 192.168.1.5
TcpTestSucceeded : True

In this sample output, the system clearly indicates that a connection was successfully established to www.example.com on port 80, signifying that both the host and port are accessible and, assuming a web service is running on port 80, that it is likely functioning correctly.

Conclusion:

The Test-NetConnection command in PowerShell serves as an invaluable tool for network diagnostics. Whether it is to attain detailed diagnostic metrics or to verify connectivity on specific ports, the command empowers users with essential information for troubleshooting and maintaining healthy network operations. By adopting these use cases, IT professionals can vastly improve their ability to diagnose network issues, ensuring connectivity and performance are maintained at optimal levels.