When configuring a firewall, two basic rules can be defined:
- Block everything
- Allow everything
It is generally advisable to block everything, only allowing explicitly what you want, as this is the more secure policy. In this case, you need to develop a configuration job prior to installation to allow those services needed for the network to operate correctly.
The allow everything rule greatly simplifies configuration and setup. However, it means you have to foresee all types of possible access that you would want to disable. Therefore, this type of policy implies more work and difficulty.