Check TCP/443 reachability with netcat

Wed, 04 Nov 2026 15:00:00 +0100

When I troubleshoot routing or firewall access, I start with a quick TCP check from the Linux VM or Kubernetes pod that needs connectivity:

nc -zv ifconfig.io 443

In my example, netcat reported succeeded! for TCP/443. That confirms a TCP connection to the resolved address for ifconfig.io from the tested client at that moment. It does not prove which route was taken, which firewall or ZTNA rule matched, or whether HTTPS/TLS works.

Listen on TCP/443 with netcat

Wed, 04 Nov 2026 13:00:00 +0100

During ZTNA testing, I used a temporary netcat listener on a Linux test host to check whether a remote connection could reach TCP/443.

nc -lvnp 443

When the connection appeared in the listener, I knew the TCP session had reached the test port. I then checked the ZTNA policy logs to confirm which access rule matched. Netcat alone cannot identify the policy that allowed the traffic.

This was a TCP connectivity check, not an HTTPS/TLS test. Binding to port 443 may require elevated permissions on Linux, and netcat syntax can vary by implementation.

Netcat on Ivan Versluis — Networknet

Check TCP/443 reachability with netcat

Listen on TCP/443 with netcat