= 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 ==

Disable the preinstalled ntp server
{{{
systemctl disable systemd-timesyncd
}}}

=== Set the Time ===
{{{
apt-get install sntp
sntp pool.ntp.org
hwclock --systohc
}}}

=== Install the NTP Daemon ===
{{{
apt-get install chrony
}}}

=== Configuration ===

Make sure chrony accepts connections from other hosts. Add the following line to `/etc/chrony/chrony.conf`
{{{
allow all
}}}

Restart chrony
{{{
service chrony restart
}}}
== 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;
}}}

== References ==
 * https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=968105