NTP Pool

Preface

In some cases you will need to configure redundant NTP connection for your Server or PC. In this case it is possible to use “pool” of NTP servers so that your NTP Client can select geographically closest NTP server (without having to configure all of the available NTP Servers).

NTP Pool creation

In general we will need to understand DNS load balancing (as well called: DNS round robin). In this case we will use one FQDN with several IP's or Alias records in DNS Zone file. According to this NTP Client has the possibility to choose one of the provided DNS records as an NTP Server

Example of zone file:

[root@DNS_Server zone]# cat example.com.db                                      # This is just an DNS Zone example
$TTL    86400
@               IN SOA  example.com root (
                                        42              ; serial (d. adams)
                                        3H              ; refresh
                                        15M             ; retry
                                        1W              ; expiry
                                        1D )            ; minimum
                IN NS           example.com.
                IN A            10.0.0.53
NTP-Server      IN A            10.0.0.3
                IN A            10.0.0.4
                IN A            10.0.0.5
NTP2-Server     IN A            10.1.0.2
                IN A            10.1.0.3

To test it, run this command:

[root@NTP-Client ~]# dig ntp-server.example.com

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6_4.6 <<>>ntp-server.example.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 21965
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;ntp-server.example.com.                        IN      A

;; ANSWER SECTION:
ntp-server.example.com.         20303     IN      A       10.0.0.3
ntp-server.example.com.         20303     IN      A       10.0.0.4
ntp-server.example.com.         20303     IN      A       10.0.0.5

NTP Client Configuration

To configure NTP Client please add in to “ /etc/ntp.conf “ file this line:

[root@NTP-Client ~]# cat /etc/ntp.conf
server ntp-server.example.com

After reload of NTPD Client Demon you shall see one of your NTP Servers as a pear to your NTPD Client Demon.

[root@NTP-Client ~]# ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*ntp-server.example.com 93.184.71.155  3 u   48  256  377   16.227    1.459  10.077

Official NTP Pool servers

Worldwide        pool.ntp.org
Asia             asia.pool.ntp.org
Europe           europe.pool.ntp.org
North America    north-america.pool.ntp.org
Oceania          oceania.pool.ntp.org
South America    south-america.pool.ntp.org

URL's

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