DHCP client protocol timing affected by NTP time change

Klemen Sladic gosturnca at gmail.com
Tue Aug 8 01:37:21 UTC 2017


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
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
of different time zone.
I have set a short lease time and noted, that from that point on, there is
no renew
requests initiated by the client.

So, I wonder, is it possible that instead of after 15 seconds the client
will try to
renew in 12 hours and 15 seconds since the time has been set 12 hours in the

Example (timeout calculation is just as an example):
1. bootup, system time Aug 8 02:00:00pm
2. start DHCP client acquire IP at Aug 8 02:01:00pm
    calculated renew on Aug 8 02:01:15pm
3. NTP at 02:01:05PM sets system time to Aug 8 02:01:05AM
4. DHCP client waits nearly 12 hours until system time is Aug 8 02:01:15pm

I will look at the source code, but just like to ask if someone knows if
this is
how it should behave or maybe I am missing something (configuration etc.).

Thank you very much in advance.

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