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.

Software

Set the Time

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

Install the NTP Daemon

apt-get install ntp

Debugging

Kiss of Death

The NTP-servers may run into to a synchronization loop. KoD (Kiss of Death) will be logged.

ntp01 /var/log/syslog

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

ntp02 /var/log/syslog

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 from a DHCP-server, the system will also ask the DHCP-server for any available NTP-servers. This causes the NTP server to synchronize time against the other NTP-server and vice versa, which again causes them to loose track of time. The solution is to tell the DHCP-client to not request the NTP information from the DHCP-server.

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

request subnet-mask, broadcast-address, time-offset, routers,
        domain-name, domain-name-servers, domain-search, host-name,
        dhcp6.name-servers, dhcp6.domain-search, dhcp6.fqdn, dhcp6.sntp-servers,
        netbios-name-servers, netbios-scope, interface-mtu,
        #rfc3442-classless-static-routes, ntp-servers;
        rfc3442-classless-static-routes;

None: NTP (last edited 2020-01-30 23:17:55 by Kristian Kallenberg)