Why when the Internet does not work, peers (IP phones) stop registering on the server?

Question

freepbx

Hello!
Yesterday I noticed such a feature of our FreePBX server:
when we lost the Internet, all IP phones in the company stopped registering on the server. On the server itself, it showed that there was registration (checked with the sip show peer NUMBER command), but the phones "fell off" and did not work.
What could it be?

Answer 1

An old problem related to DNS.
Two Solutions