Table of Contents
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
