title: VirtualBox port forwarding issue
body: <p>I'm having a strange issue with port forwarding. I've used it many times and it seems to work without issue for me (Ubuntu guest, Ubuntu host).</p>
  
  <p>I'm now dealing with a problem where a specific NodeJS-based server will curl in the guest but not the host, despite port forwarding set on that port. I'm running another server on the same box (with a different port on both guest and host) which is working normally, so I know it's not a system problem with virtualbox, etc.</p>
  
  <p>I've found numerous port forwarding questions and lots of solutions, but none of them have worked for me. I've checked that my firewall is not a problem. I've tried running both tcp and udp. I've tried changing the port from 3000 to 8123 which I know I have used successfully in the past. I've tried messing with almost every possible configuration of 0.0.0.0 and 127.0.0.1.</p>
  
  <p>Basically, I'm out of ideas and looking for other things to try. What else could cause this type of issue? Are there any other debugging strategies to try?</p>