Re: DHCP renewal changes routing table

[Dan Williams <dcbw redhat com>]

On Thu, 2015-06-04 at 13:45 +0200, Thomas Haller wrote:
> On Do, 2015-06-04 at 04:55 -0600, Nicolas Bock wrote:
> > Hi,
> >
> > When I run the Juniper Network Connect client (ncsvc) it terminates 
> > every time the DHCP license is renewed. The log files of ncsvc are 
> > unfortunately rather cryptic, but it appears as if the DHCP renewal 
> > leads to a change in the routing table which triggers a "rmon.error" 
> > in ncsvc which then tears down the VPN tunnel. Using timestamps the 
> > following two events correlate:
> >
> > 20150603133456.514649 ncsvc[p6870.t6870] rmon.error Route to 
> > destination 192.168.1.1 is missing mask 255.255.255.255 with gw 
> > 0.0.0.0, metric 1, if_id 0, disconnecting (routemon.cpp:628)
> >
> > which coincides with the following journal entries:
> >
> > Jun 03 13:34:55.454967 host NetworkManager[1805]: address 
> > 192.168.1.16
> > Jun 03 13:34:55.454985 host NetworkManager[1805]: plen 24
> > Jun 03 13:34:55.454990 host NetworkManager[1805]: expires in 300 
> > seconds
> > Jun 03 13:34:55.455026 host NetworkManager[1805]: gateway 192.168.1.1
> > Jun 03 13:34:55.455035 host NetworkManager[1805]: nameserver 
> > '192.168.1.1'
> > Jun 03 13:34:55.455210 host NetworkManager[1805]: (wlp6s0): DHCPv4 
> > state changed bound -> bound
> > Jun 03 13:34:55.456679 host dbus[1799]: [system] Activating via 
> > systemd: service name='org.freedesktop.nm_dispatcher' unit='dbus
> > -org.freedesktop.nm-dispatcher.service'
> > Jun 03 13:34:55.461372 host dbus[1799]: [system] Successfully 
> > activated service 'org.freedesktop.nm_dispatcher'
> > Jun 03 13:34:55.462021 host nm-dispatcher[8295]: Dispatching action 
> > 'dhcp4-change' for wlp6s0
> > Jun 03 13:34:56.514958 host systemd-networkd[1803]: tun0 : lost 
> > carrier
> >
> > Besides the ncsvc error listed above I sometimes also see this one:
> >
> > 20150603132151.174661 ncsvc[p6870.t6870] rmon.error Unauthorized new 
> > route to 192.168.1.0/0.0.0.0 has been added        (conflicts with 
> > our route to 0.0.0.0), disconnecting (routemon.cpp:598)
> >
> > Both seem to indicate that the routing table is changed on DHCP 
> > renewal. Is there a way to prevent networkmanager from doing this? Or 
> > is this problem caused by something else possibly?
>
> as you suspect, this is caused by NetworkManager. At various times
> (e.g. when activating a connection, or on new DHCP lease), NM will
> reinstall routes.
>
>
> recently there was a related email thread:
> https://mail.gnome.org/archives/networkmanager-list/2015
> -May/msg00016.html
>
> but no solution either.
>
>
> We could change NM not only do any system-modification when it will
> actually have any effect.
> Like, re-installing a route, only if it is not yet currently there.

In NM 1.0.x we still have nm_platform_ip4_route_sync() which already
checks array_contains_ip4_route(), so shouldn't that prevent
re-installation of device-specific routes that are already there?  Or
this is only about the default route and subnet routes from the
NMDefaultRouteManager?

Dan