[systemd-devel] Changing configurations with networkd

[Michael Olbrich]

On Wed, Jul 23, 2014 at 04:46:26PM +0200, Marcel Holtmann wrote:
> Hi Michael,
> 
> >>> I think the lease should be remembered and reused in this case.
> >> 
> >> Hm, this sounds like a bug somewhere. When the new discover is sent
> >> out it should send the same identifying information to the server, and
> >> hence be given the same lease back again. Wireshark should tell you if
> >> the fault is networkd's or the DHCP server.
> > 
> > I get the same address at first, but after several minutes the DHCP server
> > decides to offer a new address. I should note, that I have a 10 minute
> > lease time for debugging purposes, so that might make the problem more
> > prominent. I'll see if I can figure out what happens here.
> 
> look at your DHCP server and see what lease time it really hands out after reboot.
> 
> However this is between you and your DHCP server. If you configure a lease
> time of 10 minutes, then that is the only guaranteed time for a given IP
> address. There is no mandate that the server has to give you the same address
> after 10 minutes when you ask again. It is valid to just get a different one.
> And that many home routers try to give you back the same one does not mean
> that they are required to do so.
> 
> The nice DHCP servers will remember your Ethernet address and/or identity
> information and give you back your old IP address. Either with the left over
> lease time or with a brand new lease time. There is really no need to store
> this information on disk. If the lease expired the information on disk are
> stale as well. And since our DHCP implementation is so fast, it makes really
> no difference.
> 
> It is safer start out with a brand new DHCP lease instead of having to deal
> with renewal during boot. At least that way you know the DHCP server is still
> there and you have a valid IP address. Just re-using a stored IP with a
> left-over lease is not safe anyway. You never know what changed in the
> network when you were off.

I think there was some misunderstanding here. I don't want to keep the
lease across reboots. I don't care about that. I think networkd should
remember the lease when restarting networkd only and not send a new dhcp
discover.

Michael

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