[systemd-devel] systemd-resolved cannot survive router reinstall

[Anatol Pomozov]

Hi

Sorry for the delay, just got back home.

On Tue, Aug 12, 2014 at 12:19 PM, Tom Gundersen <teg at jklm.no> wrote:
> On Tue, Aug 12, 2014 at 2:48 AM, Anatol Pomozov
> <anatol.pomozov at gmail.com> wrote:
>> Thanks for the instructions, here is the log
>> https://gist.github.com/anatol/cb497118cfad6af3dc60
>>
>> The interesting entries are:
>> Aug 11 17:30:25 theserver systemd-networkd[32648]: ICMPv6 CLIENT:
>> Received Router Advertisment flags MANAGED/OTHER
>> Aug 11 17:30:25 theserver systemd-networkd[32648]: ICMPv6 CLIENT:
>> Received Router Advertisment flags MANAGED/OTHER
>> Aug 11 17:30:30 theserver systemd-networkd[32648]: ICMPv6 CLIENT:
>> Received Router Advertisment flags MANAGED/OTHER
>>
>> Is it the "heartbeat" message from the router?
>
> This is IPv6 router advertisment. Not related to your DHCPv4 problems.
>
> When the router is rebooted, we should expect to get -LOWER_UP
> followed by +LOWER_UP in the logs (same as when unplugging the cable).
> Could you try running "ip monitor link" when rebooting the rooter and
> paste whatever events you get? How about when you unplug/replug the
> cable?

I just realized that all my computers (except the home server that has
the dhcp problem) are either connected directly to router via cable or
use wifi (i.e. also connected directly). This means when router power
cycles all directly connected machines see it and thus renew the dhcp
lease. But the home server is connected via switch so it is located in
its own network segment. Even if router reboots, that segment stays
healthy and the server does not notice any "problem" with the router.
It thinks that the lease is OK. I need to unplug/plug the cable
connected to the home server - this brings networkd down/up and
eventually updates the lease.

So the problem is not in networkd, sorry for the noise. The problem is
in OpenWRT that uses dnsmasq and stores dhcp lease information on
tmpfs. If I reboot the router it looses all the leases and machines
should update the information somehow. This is a problem for machines
in a separate network segment. I can not believe that OpenWRT
developers never tested such configuration. I am going to contact
openwrt/dnsmasq maillist and ask what is the right way to solve the
issue.

PS According to off-list discussion with Tom FORCERENEW dhcp option
http://tools.ietf.org/html/rfc3203 is what suppose to fix this issue.
But dnsmasq does not support it.

PPS NetworkManager has a higher-level connectivity checking. It can be
configured to read an url content periodically and if it returns
unexpected result then connection considered broken.