PowerShell Network Test Toolkit

A PowerShell module for testing network connectivity - TCP/UDP port testing, a local port listener for validating firewall rules, and bulk testing from CSV files.

Functions

Start-PortListener

Opens a TCP listener on a specified port and logs incoming connections with timestamps. Useful for confirming that traffic from a remote host is actually reaching a server through firewalls and load balancers.

Start-PortListener -Port 443
# Listening on TCP port 443 - press CTRL+C to stop
# Address         Port  DateTime
# 10.0.0.50      49832  4/16/2026 2:30:15 PM

Test-TCPPort

Tests TCP connectivity to one or more hosts on one or more ports. Supports pipeline input and configurable timeout.

Test-TCPPort -Computer "server01","server02" -Port 80,443,3389

# Server    Port Protocol  Open Notes
# server01    80      TCP  True
# server01   443      TCP  True
# server01  3389      TCP False Connection timed out
# server02    80      TCP  True
# ...

Test-UDPPort

Tests UDP connectivity by sending a datagram and waiting for a response. Falls back to ICMP ping to distinguish between filtered ports and unreachable hosts.

Test-UDPPort -Computer "10.0.0.1" -Port 53,161

# Server    Port Protocol  Open Notes
# 10.0.0.1    53      UDP  True
# 10.0.0.1   161      UDP  True No UDP response, but host is reachable via ICMP

Test-PortsFromCSV

Bulk-tests outbound connectivity from a CSV of firewall rules. Column names are configurable to match your CSV layout.

Test-PortsFromCSV -Path ".\firewall_rules.csv" -DestinationColumn "Dest IP" -PortColumn "Dest Port" -DirectionColumn "Direction"
# Testing 47 outbound rules...
# Results: 45 passed, 2 failed out of 47 tests

Installation

# Copy the module to your PowerShell modules directory
Copy-Item -Path .\NetworkTestToolkit.psm1 -Destination "$env:USERPROFILE\Documents\WindowsPowerShell\Modules\NetworkTestToolkit\NetworkTestToolkit.psm1"

# Or import directly
Import-Module .\NetworkTestToolkit.psm1

CSV Format

For Test-PortsFromCSV, the default expected columns are Destination, Port, and Direction. Only rows where Direction contains "outbound" are tested. Use the -DestinationColumn, -PortColumn, and -DirectionColumn parameters if your CSV uses different column names.

Destination,Port,Direction
10.0.0.1,443,Outbound
10.0.0.2,1433,Outbound
10.0.0.3,80,Inbound

Use Cases

• Firewall change validation - after a firewall change, bulk-test all expected rules from a spreadsheet
• Migration readiness - verify connectivity from a new environment before cutover
• Troubleshooting - run the listener on one side and test from the other to isolate where traffic is being dropped
• Audit - periodically test that expected ports are still open (or closed)