[BusyBox] Lease remembering in udhcpc?

Rainer Weikusat rainer.weikusat at sncag.com
Mon Aug 22 08:33:46 UTC 2005

Josef Wolf <> writes:
> On Sun, Aug 21, 2005 at 06:17:58PM +0200, Rainer Weikusat wrote:
>> The second is not so easy, though, because all times in DHCP are
>> relative to the beginning of a particular negotiation cycle, which
>> means that the client can neither reliably determine if the lease is still
>> valid (the host clock could have changed arbitrarily in the meantime)
> Umpf... I can't believe you're really worrying about the clock.

The people who wrote the DHCP specification apparently did. 

> I understand that DHCP times are relative. But this doesn't mean that
> they can't be converted to a more sane format.

RFC2131 gives a rationale for this:

	3.3 Interpretation and representation of time values


          As clients and servers may not have synchronized clocks, times are
	  represented in DHCP messages as relative times, to be interpreted
	  with respect to the client's local clock. 

It is certainly possible to disagree with this rationale, but this is
then against the specification. Furthermore, the DHCP client cannot
'cope' with clock changes it has no knowledge of. It can ignore them,
and thereby possibly interfere with some administrators policy
descision. I'd agree that it is unlikely that this will actually
happen in practice, but it is nonetheless possible.                  

>> nor does it know if it is still usable at all (client might be running
>> on a different subnet).
> So what? it _might_ be on a different subnet. But in 99.9999% it will be
> on the _same_ subnet.  But even _if_ it happens to be on a different
> subnet: what's the problem?

This depends on what you consider to be "a problem": The behaviour is
incorrect with reference to the specification. This is something you
may or may not care for, but should still (IMHO) know about, if you
write code that interoperates with devices that implement this

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