Steam link firewalld config file. Place in /etc/firewalld/services.

steam-link-server.xml

<?xml version="1.0" encoding="utf-8"?>
<service version="1">
  <short>steamlink</short>
  <description>Server side to allow steam link in home streaming to be able to connect.</description>
  <port protocol="udp" port="27031"/>
  <port protocol="tcp" port="27036"/>
  <port protocol="tcp" port="27031"/>
  <port protocol="udp" port="27036"/>
  <protocol value="tcp"/>
</service>