Virtualization

If you have a small network and you are using Citrix XenServer, then you might want to use it as your time server. It’s important that your XenServer has proper time for your VMs, so why not go one step further. You can have it as the main source of time, even for your primary domain controller. I would even set up an alias on your DNS server named: time

To set up XenServer for serving time, there are only a couple things you need. First I recommend reading over Citrix’s documentation real quick to get a high level view of things: CTX116307

Edit your /etc/ntp.conf and set it up for the time servers you want to sync with.

Here is a sample output of: nano /etc/ntp.conf

server 0.pool.ntp.org
server 1.pool.ntp.org
server 2.pool.ntp.org
server 3.pool.ntp.org

restrict 192.168.0.0 mask 255.255.0.0 nomodify notrap

Restart the time service:
service ntp restart

Make sure the service starts up when the server reboots:
chkconfig ntpd on

Check that your server is synchronizing time, this may take a few minutes (look for the * on the left of the hostname):
ntpq -p
The last part of this process involves opening up UDP port 123 on XenServer’s firewall, iptables, so that hosts can grab the time from our server.

nano /etc/sysconfig/iptables

Add the following line before the REJECT rule (usually the last line): -A RH-Firewall-1-INPUT -p udp –dport 123 -j ACCEPT

Finally you can restart the iptables service and begin testing from another host on your network using: ntpdate -b time.yournetwork.com.

service iptables restart

Please feel free to comment and leave suggestions if you have an issue.