DHCP client protocol timing affected by NTP time change

Pavel Zhukov pzhukov at redhat.com
Tue Aug 8 12:29:46 UTC 2017

Eugene Grosbein <eugen at grosbein.net> writes:

> 08.08.2017 8:37, Klemen Sladic wrote:
>> Hi.
>> I am experiencing an interesting problem with DHCP client timeouts.
>> When the system boots up it set its date/time, starts DHCP client and NTP client.
>> Only after the DHCP client interface is configured, the NTP client is able to access
>> the NTP server.
>> In my case, when NTP client adjusts the date/time it is set 12 hours back because
>> of different time zone.
> That's plain wrong and that's a root of your problem.
> In no way a time zone difference should affect NTP time and kernel
> time.
Unfortunately it's not. Some systems keep local time in RTC. dhcp code
widely uses gettimeofday() and it's well known issue. Besides of that
there are systems without RTC at all (and OS can have lifetime per
interface and end up without IP address at all).

For example:

> The only case it could happen that's client keeping local time in its RTC
> instead of UTC time. Fix it to keep UTC time in the RTC and it will be fine.
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