Telnet connection refused

I have a server on Ubuntu 14.04 listening on port 8443.

curl GET https://localhost:8443 --insecure works fine, same for wget with --no-check-certificate.

However if I try to connect to the server from any other machine, it won’t work.

Running telnet server_name 8443 from another Ubuntu machine which is in the same LAN gets me:

telnet: Unable to connect to remote host: Connection refused.

How can I fix this?

What’s need to be done in order to open the port?

Bruteforce https post using single tcp connection

So I’ve tried bruteforcing my server using thc-hydra’s https-post-form, but it floods the server very quickly and the requests start timing out.

However, If I go through the browser where the HTTP header Connection: Keep Alive is used and accepted by the server, I can make a lot of requests in rapid succession without flooding the server.

Is there a tool like hydra that can be used to send many https post requests using a single tcp connection?

Authentication of network connection failed when connecting to the internet

Authentication of network connection failed when connecting to the internet. I tried changing the DNS, Forgetting the network and connecting again, restarting my laptop and connecting to different neyworks but the same error kept happening. I am running Ubuntu 19.0.4 on an Acer Aspire E5-771 Series notebook.