When running remote Git commands or SSH, your connection might time out:
$ ssh -vT git@github.com
> OpenSSH_8.1p1, LibreSSL 2.7.3
> debug1: Connecting to github.com [207.97.227.239] port 22.
> debug1: connect to address 207.97.227.239 port 22: Connection timed out
> ssh: connect to host github.com port 22: Connection timed out
> ssh: connect to host github.com port 22: Bad file number
Solving the issue
Use HTTPS
Often, the simplest solution is to simply avoid SSH entirely. Most firewalls and proxies allow HTTPS traffic without issue. To take advantage of this, change the remote URL you're using:
$ git clone https://github.com/USERNAME/REPO-NAME.git
> Cloning into 'reponame'...
> remote: Counting objects: 84, done.
> remote: Compressing objects: 100% (45/45), done.
> remote: Total 84 (delta 43), reused 78 (delta 37)
> Unpacking objects: 100% (84/84), done.
Test from a different network
If you can connect the computer to another network that doesn't have a firewall, you can try testing your SSH connection to GitHub Enterprise Cloud. If everything works as it should, contact your network administrator for help on changing the firewall settings to allow your SSH connection to GitHub Enterprise Cloud to succeed.
Using SSH over the HTTPS port
If using HTTPS is not an option, and your firewall admin refuses to allow SSH connections, you can try using SSH over the HTTPS port instead.