title: Can't connect to specific (VPN) subnet from within docker containers
body: <p>Okay so I have a weird issue. Tl:dr; Whenever I try to access a specific subnet behind the company VPN I can access it just fine from the host system, but not from within any docker containers.</p>
  <p>Tried the same steps on Manjaro with KDE, Ubuntu 20.04 with Gnome. Not working on either. <em><strong>Works</strong></em> without config changes on Windows.</p>
  <h2>What I'm trying to do</h2>
  <ul>
  <li><p>On host system:
  <code>psql -h 10.4.red.acted -p 5433</code> gives a password prompt as intended</p>
  </li>
  <li><p>If I create a bare alpine container (<code>docker run -it alpine sh</code>), install postgresql and run the exact same command there's no prompt (no output at all) until a timeout after a couple minutes.</p>
  </li>
  <li><p>In an existing container, if I run the exact same command, or have the application handle the connection, it times out without prompt</p>
  </li>
  </ul>
  <h2>What I tried</h2>
  <p>I added a daemon.json file with a custom bip setting. That didn't change anything.</p>
  <p>I checked the subnets, they don't overlap with the docker subnet. I tried setting the subnet to 192.168.*, that didn't change anything.</p>
  <p>I checked my iptables for any blocks on port 5433 or the docker subnet. Nothing. I can't access the iptables of the server, but I can't imagine that is the issue, as connecting from the host OS works without issue.</p>
  <h2>What I know to be working</h2>
  <p>If I run the barebones alpine container with <code>docker run --network host -it alpine sh</code> I get a password prompt, it's working!?</p>
  <h3>My conclusion</h3>
  <p>This leads me to believe I need to figure out why docker won't connect to the host OS network, but that's where I'm stuck. I can't find any resources that aim towards solving this issue on a global scale. I don't want to (and in some applications am not allowed to) change docker-compose files or set custom run commands in the dockerfiles to get this to work. Am I wrong in thinking that this should just work on default config? Did I make a mistake in installing docker/docker-compose?</p>
  <p>Any pointers would be greatly appreciated.</p>