Like the DHCP server, NTP requires only firewall rules to operate (no SELinux configuration is necessary).
The NTP service uses TCP and UDP port 123, so you need to open both on the firewall.
Step 1. Use iptables to create the required firewall rules:
# iptables -I INPUT 5 -p udp -m udp –dport 123 -j ACCEPT
# iptables -I INPUT 5 -p tcp -m tcp –dport 123 -j ACCEPT
Step 2. Save the firewall rules you just created:
# service iptables save
Saving firewall rules to /etc/sysconfig/iptables: [ OK ]
Step 3. Then restart the iptables service:
# service iptables restart
iptables: Flushing firewall rules: [ OK ]
iptables: Setting chains to policy ACCEPT: filter [ OK ]
iptables: Unloading modules: [ OK ]
iptables: Applying firewall rules: [ OK ]