The Nessus user interface uses port 8834. If not already open, open port 8834 by consulting your firewall vendor's documentation for configuration instructions.
If you configured the Nessus server on a host with 3rd-party firewall such as ZoneAlarm or Windows firewall, you must configure it to allow connections from the IP addresses of the clients using Nessus.
Nessus and FirewallD
You can configure Nessus to work with FirewallD. When you install Nessus on RHEL 7, CentOS 7, and Fedora 20+ systems using firewalld, you can configure firewalld with the Nessus service and Nessus port.
To open the ports required for Nessus, use the following commands:
>> firewall-cmd --permanent --add-service=nessus
>> firewall-cmd --reload