On Sun, Sep 2, 2012 at 8:37 AM, Earl Ramirez earlaramirez@gmail.com wrote:
On Sun, 2012-09-02 at 07:46 +0000, Artifex Maximus wrote:
Hello!
I would like to setup an NTP server for my Windows network using CentOS 6.3 with firewall turned on. As I learned the NTP protocol uses port 123 UDP. I have two NIC cards. One for internal network and one for access internet. Both cards in private address range. The problem is when I am using firewall described below the client cannot access the server. No idea why. Without firewall everything works flawless. So the problem is not in the NTP configuration. No idea why but with disabled firewall the first query gives error but all other query is work. I am using arpwatch to see what is happen on network (new machines and so). Not know is that related to the problem or not.
First I had used the system-config-firewall generated firewall (standard firewall with port 123:udp added). No success, client cannot connect.
Next I made a script for myself and saved with 'service iptables save' command. The configuration is:
eth0 10.0.0.99/24 eth1 10.0.1.10/24
The script for making firewall rules: iptables -P INPUT ACCEPT iptables -F iptables -A INPUT -i lo -j ACCEPT iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT iptables -A INPUT -p tcp --dport 22 -j ACCEPT iptables -A INPUT -i eth0 -s 10.0.0.0/24 -p udp --dport 123 -j ACCEPT iptables -A INPUT -i eth0 -s 10.0.0.0/24 -p tcp --dport 123 -j ACCEPT iptables -A INPUT -m limit --limit 5/min -j LOG --log-prefix "iptables denied: " --log-level 7 iptables -A INPUT -j DROP iptables -P FORWARD DROP iptables -P OUTPUT ACCEPT
I might be wrong but I think you need to add the IP Address of the NTP server
Why? I am using a more general form of INPUT rule.
you can also use tcpdump to capture the traffic between the clients and the ntp server to see what is being blocked.
Thanks for your answer. Good idea and I'll do it.
# iptables -A OUTPUT -o eth0 -p udp -s <client IPs> --sport 123 -d <NTP Server IP> --dport 123 -m state --state NEW -j ACCEPT.
I am using
iptables -P OUTPUT ACCEPT
which allows all OUTPUT traffic on all interface as default rule. So I do not think that I need any more specific rule.
Bye, a