Recommended Number of NTP Servers

Richard Laager rlaager at
Mon Nov 4 09:27:13 UTC 2019

The default for maxclock is 10. This includes the "pool" entries, of
which the stock Debian configuration has four:
pool iburst
pool iburst
pool iburst
pool iburst

As a result, the default is to use 6 pool servers. says
"the general rule is for 2n+1 to protect against 'n' falsetickers". (It
goes on to discuss the exception for n=1, which is not relevant here.)

If that's true, then it seems like odd numbers of servers are better,
all things being equal. From there, it seems like I should set maxclock
to either 11 (so 11-4 = 7 servers) or 9 (so 9-4 = 5 servers). Any flaws
in this logic?

Any thoughts on whether 7 servers or 5 servers is better? The same page
says, "Conventional wisdom is that using at least five upstream time
servers would probably be a good idea, and you may want more." The
conservative choice is 7, but is that likely to make a meaningful
difference compared to 5?


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