Expect it is not just configuration. It is hardware too. I am member in a internet provider by students. We couldn't allow an UDP since we have an agreement with our uplink that we will make it impossible to host outwards facing services. To guarantee that for UDP we would need a stateful firewall, which we didn't have. Due to agreements without uplink they want to have full access to our firewall and since they only use Cisco, we are required to do so too. This means we had to shell out €€€€€ to get a firewall from Cisco and we had to put aside money to do that for years. Then our (old) core router had 90%+ load during testing of the firewall since the hardware UDP support it supposedly had was not up for the task. So we had to buy a second core router where we lucky weren't bound to Cisco due to outside obligations another €€€€ investment. It's not just stupid configuration, sometimes it is just means and it takes long strategic planning we can do as a non-profit to afford such things.