Scenario 1 — IIS default website bound to 443 blocking Veeam

She considered running Veeam on port 8443 internally, then setting up an IIS ARR (Application Request Routing) reverse proxy on port 443 that forwarded traffic. Elegant in theory. In practice, Veeam’s API hard-codes redirect URLs in its authentication handshake. The moment the proxy forwarded a request, Veeam would generate a callback URL with :8443 , the browser would throw a CORS error, and backup jobs would fail with cryptic "token mismatch" errors.

John checked the list of running processes on the server and found that a new application, called "Acme Secure Gateway", had been installed by a colleague a few days ago. The application was designed to provide secure access to the company's network, but it appeared to be using port 443, which was causing the conflict with Veeam.

Locate port 443 and look at the column to see the executable name. ⚠️ Common Culprits Occupying Port 443

If the server is multi-role and the application currently using Port 443 cannot be changed (e.g., a critical internal web portal), you can configure Veeam to use alternate ports. However, be aware that this may complicate firewall rules and is not supported for Veeam Cloud Connect providers.

Sometimes, the port is reserved by the system’s HTTP driver ( http.sys ).

Suggested success metrics

Now you know the name of the offender.