By default, when server instances are created, all inbound and ountbound networking is disabled. You can allow certain types of network traffic by using Security Groups.
What about the Default security group?
This group allows for all outbound networking. We suggest attaching this security group to your server except if your server is to solely communicate on the local LAN.
Several other default security groups exist for common use cases, such as for HTTP, HTTPS, and SSH traffic when creating your Cloud instances.
If these security groups were selected during Cloud instance creation they can be attached to any server instances, otherwise they can be defined manually, under Server / Network / Security groups:
