ntp servers

Glenn Satchell glenn.satchell at uniq.com.au
Tue Oct 8 01:43:48 UTC 2013

On Tue, October 8, 2013 6:11 am, Doug Barton wrote:
> On 10/07/2013 12:07 PM, Gary Johnson wrote:
>> On 2013-10-07, Steven Carr wrote:
>>> On 7 October 2013 01:01, Julie Xu <xll40 at hotmail.com> wrote:
>>>> what is default for option ntp-servers? option 4 ? 42 ? or both?
>>> NTP is option 42, option 4 is for the older time protocol.
>>> But the DHCP clients need to be configured to request/use that option.
>>> This is usually the case on Linux, but on Windows if the client is a
>>> member of Active Directory it will use the Domain Controller for time
>>> sync. Supposedly if a Windows machine is not a member of AD it will
>>> use option 42, but I've never seen that work. From what I've seen on
>>> OS X setting NTP via DHCP isn't supported.
>> I believe NTP is 56.  42 is the TZDB Timezone option, and 41 is the
>> POSIX Timezone option.
> There is no need to guess :)
> https://www.iana.org/assignments/bootp-dhcp-parameters/bootp-dhcp-parameters.xhtml#options

That's a very useful list, but there is no need to even know that. dhcpd
already knows which option to use. See dhcp-options man page:

     option ntp-servers ip-address [, ip-address... ];

       This option specifies a list of  IP  addresses  indicating
       NTP  (RFC  1035) servers available to the client.  Servers
       should be listed in order of preference.


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