Verifying Connectivity - Testing Port Connectivity

Tools for Transport Layer Connectivity Testing

Netcat (Linux and macOS)

• Purpose: Tests connectivity at the transport layer.
• Command: nc
• Mandatory arguments:
  • host: The target host.
  • port: The target port.
• Example: nc google.com 80 attempts to establish a connection on port 80 to google.com.
  • If the connection fails, the command exits.
  • If the connection succeeds, a blinking cursor appears, allowing you to send application layer data.
• Flags:
  • -z (zero input/output mode):
    • Checks the status of a port without sending data.
  • -v (verbose):
    • Provides human-readable output.
    • Useful for determining if a connection to the port is possible.
• Example with flags: nc -z -v <host> <port>

Test-NetConnection (Windows)

• Purpose: Similar functionality to Netcat.
• Basic Usage: Test-NetConnection <host>
  • Defaults to using ICMP echo request, similar to ping.
  • Displays more data than ping, including the data link layer protocol.
• Port Connectivity Testing: Test-NetConnection <host> -Port <port>
  • Tests connectivity to a specific port.

Additional Notes

• Both Netcat and Test-NetConnection have functionalities beyond simple port connectivity tests.
• Further reading is recommended to explore their full capabilities.