Many public git repositories have several alternate URLs; for instance, the kernel.org repositories have git://, https://, and https:// URLs.
The common URL schemes for git repositories are:
ssh:// – default port 22
git:// – default port 9418
https:// – default port 80
https:// – default port 443
Above list gives you the respective ports which needs to be kept open on the firewall to be able use your Git repositories.
The git:// protocol uses port 9418, so you should make sure your firewall allows outbound connections to this port.
If you use csf ensure this port is enabled in TCP_IN and TCP_OUT.
To test if the git:// is working you can try the following command on the server
netstat -ntpl|grep -i 9418
To test it externally you can telnet to the port for the respective server’s ip.