Why is no configuration required for Elastix, which is behind NAT?

Question

Asterisk

Began to understand IP telephony. And today there was a task to install Elastix, several internal phones, in general, everything is simple. Well, since I heard everywhere that Asterisk, which is located behind NAT, needs to be configured in a special way, I thought that today I will configure it all and at the same time figure it out.
But it was not there. I just installed Elastix, created a trunk, extensions, incoming / outgoing routing for calls. and all with a minimal configuration, and it all worked.
The network is: Provider> Dlink-dir300> Elastix, phones, computers.
Question: Why does everything work with standard settings without any port forwarding and settings for Asterisk, although it is behind NAT? What do I not understand?

Answer 1

because during the installation process, modern electrics
1) includes stun (helps to find out the external address)
2) includes nat=comedia
+your provider, most likely, requires registration, in fact,
this is enough for normal routers.