A few days ago I noticed that the system clock on one of my machines was off by about 90 seconds compared to my smartphone and other machines. Long story short, ntpd.service was not properly being loaded by systemd. To quickly sync my system I manually ran sudo ntpd as a temporary work-around until I fix the issue.
In a Google search for configuring ntp, I learned that the user can specify which ntp servers to update from by editing /etc/ntp.conf. Naturally I thought it would be a good idea to use the Asia pool of ntp servers for geographical proximity reasons.
When I visited http://www.pool.ntp.org/en/ I saw the following stats for the number of ntp servers worldwide (current as of 2014-05-12):
North America 858
South America 39
All Pool Servers 3748
The vast majority of Network Time Protocol servers are located in Europe, followed by N. America (Europe has almost 3 times as many servers as N. America). I was kind of surprised to see that despite giant countries like India and China residing in Asia, there are only 217 active ntp servers in the region.
A closer look at the Asia ntp pool reveals the following:
Philippines — ph.pool.ntp.org (1)
Malaysia — my.pool.ntp.org (4)
Turkey — tr.pool.ntp.org (27)
Singapore — sg.pool.ntp.org (14)
India — in.pool.ntp.org (12)
Hong Kong — hk.pool.ntp.org (12)
United Arab Emirates — ae.pool.ntp.org (0)
Japan — jp.pool.ntp.org (38)
Bangladesh — bd.pool.ntp.org (10)
Israel — il.pool.ntp.org (1)
Korea — kr.pool.ntp.org (5)
Thailand — th.pool.ntp.org (12)
Iran — ir.pool.ntp.org (5)
Taiwan — tw.pool.ntp.org (18)
China — cn.pool.ntp.org (13)
Indonesia — id.pool.ntp.org (28)
Vietnam — vn.pool.ntp.org (5)
Pakistan — pk.pool.ntp.org (2)
Oman — om.pool.ntp.org (0)
Uzbekistan — uz.pool.ntp.org (2)
Sri Lanka — lk.pool.ntp.org (5)
Kyrgyzstan — kg.pool.ntp.org (2)
Cambodia — kh.pool.ntp.org (5)
Qatar — qa.pool.ntp.org (1)
Saudi Arabia — sa.pool.ntp.org (2)
Iraq — iq.pool.ntp.org (2)
Kazakhstan — kz.pool.ntp.org (9)
Maldives — mv.pool.ntp.org (4)
Kuwait — kw.pool.ntp.org (0)
China (13), India (12), and Korea (5) have a surprisingly low number of ntp servers for their size and/or level of economic development. Japan is number one in the region with 38 servers, followed by Indonesia (28), then Turkey (27).
Looking at the statistics over time for Asia, 180 days prior to May 12, the number of active servers fell by 57(!). I wonder what caused this huge decrease from 277 to 220 active servers (a fall of just over 20%)...
Perhaps DDOS issues described in CVE-2013-5211 ("exploited in the wild in December 2013" -- note that this is 6 months before May 2014) related to malicious monlist requests?
Looking at the statistics for all regions except S. America, 180 days ago the number of ntp servers fell across the board, though it seems that the Asia pool was hardest hit.