/usr/lib/firewalld/services/ Current File: //usr/lib/firewalld/services/dns.xml

<?xml version="1.0" encoding="utf-8"?>
<service>
  <short>DNS</short>
  <description>The Domain Name System (DNS) is used to provide and request host and domain names. Enable this option, if you plan to provide a domain name service (e.g. with bind).</description>
  <port protocol="tcp" port="53"/>
  <port protocol="udp" port="53"/>
</service>