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Recipe 19.5. Deciding Which NTP Pools to Use19.5.1 ProblemSo you'd like to know about other choices for ntp pools. It seems that connecting to a global pool runs the risk of using servers that are too far away for good performance. 19.5.2 SolutionThere are three classes of ntp pools available:
There is not yet a definitive list of country pools. You can check to see if one exists for your country with ping: $ ping nl.pool.ntp.org
PING nl.pool.ntp.org (194.109.206.206): 56 data bytes
64 bytes from 194.109.206.206: icmp_seq=0 ttl=49 time=240.8 msSee http://www.iana.org/cctld/cctld-whois.htmfor a list of country codes. As a general rule, use a pool when it has at least three servers. You can find this out with dig: $ dig de.pool.ntp.org
; <<>> DiG 9.2.4rc2 <<>> de.pool.ntp.org
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 13116
;; flags: qr rd ra; QUERY: 1, ANSWER: 8, AUTHORITY: 6, ADDITIONAL: 6
;; QUESTION SECTION:
;de.pool.ntp.org. IN A
;; ANSWER SECTION:
de.pool.ntp.org. 5400 IN A 81.169.174.99
de.pool.ntp.org. 5400 IN A 134.99.176.3
de.pool.ntp.org. 5400 IN A 195.185.228.210
de.pool.ntp.org. 5400 IN A 213.133.108.8
de.pool.ntp.org. 5400 IN A 217.160.141.61
de.pool.ntp.org. 5400 IN A 80.190.100.192
de.pool.ntp.org. 5400 IN A 80.237.234.15
de.pool.ntp.org. 5400 IN A 81.169.158.205
...To investigate further, run ping a few times to get an idea of roundtrip times: $ ping de.pool.ntp.org
PING de.pool.ntp.org (217.204.76.170): 56 data bytes
64 bytes from 217.204.76.170: icmp_seq=0 ttl=238 time=221.7 ms
64 bytes from 217.204.76.170: icmp_seq=1 ttl=238 time=224.3 ms
64 bytes from 217.204.76.170: icmp_seq=2 ttl=238 time=223.8 msThen run traceroute a few times. Track the number of hops, and look for timeouts: $ traceroute de.pool.ntp.org
traceroute: Warning: de.pool.ntp.org has multiple addresses; using 199.184.165.135
1 80.239.142.1 (80.239.142.1) 0.236 ms 0.129 ms 0.115 ms
2 ge-0-2-0.pr1.k88.fra.de.eurotransit.net (82.96.89.245) 0.317 ms 0.259 ms 0.248 ms
3 ffm-k88-i2-geth3-2.telia.net (213.248.79.65) 0.417 ms 0.243 ms 0.241 ms
...
11 195.185.228.210 (195.185.228.210) 9.191 ms 8.925 ms 9.094 ms11 hops and no timeouts is pretty good. Each test should be run several times to get a reasonably accurate picture. 19.5.3 DiscussionThe nice thing about using the ntp pools is that they do the work for you. Once your system is configured, you shouldn't have to fuss with it. And time server abuse is mitigated, so everyone is happy. If you have a good full-time Internet connection and want to be part of a pool, see http://www.pool.ntp.org for the details. The more time servers there are, the less load there is on each one. 19.5.4 See Also
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