Centos ntpd can't sync [closed]
Your remote peers are unreachable. This might be because of a local restriction in /etc/ntp.conf, a local firewall setting, or an upstream firewall setting or connectivity issue between you and your NTP servers.
The contents of your /etc/ntp.conf and iptables diagnostics indicate that the problem isn't likely your local configuration. Your tcpdump -ni eth0 'udp port 123' confirms that the packets are leaving your system successfully, but aren't being replied to.
So it seems like you have an upstream connectivity problem.