NTP

Keeping time is important. Especially when debugging an issue between servers. It is a pain comparing logfiles with a time skew. For that reason we will configure two NTP servers that all clients will synchronize their time to.

Configuring a redundant NTP server does not really make any sense. The DHCP server sends option ntp-servers to the DHCP clients, so if one NTP server is down, then the other will get the request instead.

Network

The NTP servers will have fixed IP-addresses. That is configured in the DHCP servers list of statically assigned IP-adresses by using the Domains MAC address.

• 192.168.1.40 ntp01
• 192.168.1.41 ntp02

Software

Set the Time

apt-get install ntpdate
ntpdate pool.ntp.org
hwclock --systohc

Install the NTP Daemon

apt-get install ntp

Debugging

If the following show up in the NTP servers log, the NTP server is synchronizing against itself.

Jan 30 06:39:30 ntp01 ntpd[464]: receive: KoD packet from 192.168.1.41 has inconsistent xmt/org/rec timestamps. Ignoring. Jan 30 07:04:15 ntp02 ntpd[511]: receive: KoD packet from 192.168.1.40 has inconsistent xmt/org/rec timestamps. Ignoring.

While getting its IP-address via DHCP, the system will also ask the DHCP-server for any available NTP-servers. This causes the NTP server to synchronize time against itself, which again causes it to loose track of time. The solution is to tell its DHCP-client to not request the NTP information from the DHCP-server.

Make the following changes in /etc/dhcp/dhclient.conf

        #rfc3442-classless-static-routes, ntp-servers;
        rfc3442-classless-static-routes;