Follow these steps to add a rule to iptables to allow incoming connections on port 9998:

Edit iptables:

# vi /etc/sysconfig/iptables

Find the following line in the file:

 -A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited

Add the following line BEFORE the above line:

-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 9998 -j ACCEPT

Restart iptables:

# service iptables restart


Other Port related articles:

Required Ports for the Uptime Infrastructure Monitor Monitoring Station

What ports need to be open to add an ESX or vCenter system to Uptime Infrastructure Monitor?

What ports are required for WMI agentless monitoring

Changing the Windows Agent Port

Configuring SQL Server Ports