[ntp:questions] [Pool] NTP Pool Servers and DynDNS

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Thu May 12 21:22:59 UTC 2011


On Fri Feb 4 2011 Dave Hart wrote in [Pool]:
> Vincent Zweije wrote:
>> Dave Hart wrote:
>>> In my view, it would be good for ntpd to keep track of
>>>  the hostname originally used to configure the association
>>>  and (at least by default) use leftover alternate
>>>  addresses or re-resolve the name after the association
>>>  becomes unreachable.
>>
>> Wouldn't it be better to re-resolve when the DNS record
>>  TTL expires?  Provided the resolver library gives access
>>  to the TTL, of course.
>
> It doesn't, in our case.  ntpd name resolution is built on
>  getaddrinfo() which provides an answer but not a time remaining.
> Moreover, it's risky to re-resolve before using all addresses,
>  or you might end up stuck using only the first (few) of
>  the addresses.
>
> Anyway, this is a detail of an imaginary capability.
>  We can hash out a solution once ntpd actually re-resolves
>  non-pool hostnames.

Why not just use the pool directive instead of the server directive?
  (or have NTP internally do so.)
 {Even if / when they only resolve to one IP each.}

Is there any significant down side to doing:
 # ntpd 4.2.7
 restrict source nomodify
 pool ntp.example.com          # [192.0.32.10]
 pool cronos.example.net       # [198.51.100.11]
 pool tempus.example.org       # [203.0.113.18]
 pool time.example.edu         # [169.254.132.33]
 pool clock.example.test       # [192.0.2.123]
 pool tick.example.localhost   # [127.254.123.60]
 pool tock.example.invalid     # []
 pool 0.zone.pool.ntp.org      # [###.###.###.#], [###.##.###.##], [###.#.###.###]

instead of:
 # ntpd 4.2.7
 restrict source nomodify
 server ntp.example.com        # [192.0.32.10]
 server cronos.example.net     # [198.51.100.11]
 server tempus.example.org     # [203.0.113.18]
 server time.example.edu       # [169.254.132.33]
 server clock.example.test     # [192.0.2.123]
 server tick.example.localhost # [127.254.123.60]
 server tock.example.invalid   # []
 pool 0.zone.pool.ntp.org      # [###.###.###.#], [###.##.###.##], [###.#.###.###]

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