setting ntp with dhcp

Giovane C. M. Moura giovane.moura at
Mon Oct 4 07:18:24 UTC 2021

Thanks everyone for their answers.

To summarize:

 1. NTP from DHCP usage:
    * Not all clients accept DHCP configs for NTP (like android phones)
    * WiFi VoIP phones use ntp from dhcp (default) -- Google Fiber case

      showed that VOIP phones may fail to register if DHCP provides 	
      unreachable NTP servers.
2. DOCSIS devices use TIME protocol, and sometimes NTP as well
3. Most devices likely to use hard-coded values

I'm approaching this a researcher, trying to understand these settings
usage in the wild.

W.r.t. Hal Murray bursts queries, that's interesting, we also run some
servers that we share on the NTPPool but we don't see such bursts -- we
see sort of a stable timeseries with thousands of NTP queries per second.

thanks everyone for sharing their thoughts and experiences,


On 10/1/21 5:05 PM, Mukund Sivaraman wrote:
> Hi Giovane
> On Fri, Oct 01, 2021 at 04:12:15PM +0200, Giovane C. M. Moura via NANOG wrote:
>> hello folks,
>> So DHCP can also be used to set NTP servers on clients, for both
>> IPv4[rfc2132] and IPv6[rfc5908].
>> I'm looking for statistics on setting NTP servers on clients using DHCP,
>> in the wild. Does anyone know if there is any available somewhere?
>> I'm also looking for reports from operators and their experiences on
>> this, and why they use (or not) this DHCP feature, and what types of
>> networks is this deployed, and their motivations, etc.
> Some PC OSs such as Linux distributions obey the "ntp-servers" ISC DHCP
> option (mapped to option code 42 in RFC 2132 section 8.3) and configure
> the client's NTP service with it.
> But not all DHCP clients do. E.g., Android phones ignore this option
> completely.
> We use this option in our office to configure a local timeserver (uses a
> Garmin GPS 18x LVC receiver), but it only works on client machines that
> attempt to make use of that option.
> 		Mukund

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