Drush download, what port does it use?

I work on a Drupal 7 intranet site for a large company. The firewall on the server it is housed on currently does not allow any access to the Internet. I’ve been upgrading Drupal core and modules by downloading them to my pc and accessing the server with remote desktop client.

What are the most minimal holes that we’d have to punch in the firewall for Drush to be able to download updates from drupal.org.

Would just opening up port 22 do the trick?