Recommended Number of NTP Servers

[James Browning]

On Mon, Nov 4, 2019, at 5:23 PM Richard Laager via devel <devel at ntpsec.org>
wrote:

> Each of these names (N.debian.pool.ntp.org) resolves to only 4 IPs.* The
> four of them resolve to (mostly) non-overlapping IPs. In other words, if
> I resolve only one name, I get 4 IPs, but if I resolve all four names, I
> get 15 IPs. If I wait 150 seconds for the TTL to expire, I do get more
> IPs. But using all four names definitely gets me IPs a lot faster, which
> makes a difference for initial convergence.
>
> * I'm ignoring IPv4 vs IPv6 here and considering only one address
> family, which is relevant to IPv4-only hosts. Though apparently only one
> of the four names is returning AAAA records.
>

That would be N=2. You only need to wait for the timeout to expire if
you are using a caching resolver (you are). If one of the nameservers
for the pool is directly asked (you should not) you can get answers
faster.
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