[Dnsmasq-discuss] OpenWRT, modem restarts and lost dhcp leases

[Anatol Pomozov]

Hi

This is a follow-up for a discussion that I had in systemd maillist
[1]. Here is description of the problem:

I have a router (Archer C7 V2) where I use patched version of OpenWRT.
It uses dnsmasq as a dhcp server for my local network. OpenWRT uses a
file on tmpfs to store the dhcp leases. When I reboot modem the files
on tmpfs are lost and dnsmasq needs to build the dhcp lease database
from anew. All the machines that are connected directly to the modem
(via cable or via wifi) work fine here - they notice that data link
went down and when it gets back they update DHCP information.

The problem is when some machine is located in a different network
segment. In this case the data layer stays healthy, machine does not
notice anything wrong with the network and dhcp client does not update
DHCP lease at the router. So I cannot ping my machine by the name
anymore, pinging by ip works fine. To update the lease I need to power
cycle the ethernet switch that serves that network segment. But of
course it is not the best solution.

So my question what is the solution for such problem? Should dnsmasq
ask on start all the machines to update their dhcp leases? Is it what
FORCERENEW option is? I see that FORCERENEW is not implemented in
dnsmasq.

[1] http://lists.freedesktop.org/archives/systemd-devel/2014-August/022363.html