Re: DHCP renewal changes routing table

On Thu, Jun 4, 2015 at 6:07 AM, Thomas Haller <thaller redhat com> wrote:
On Do, 2015-06-04 at 05:56 -0600, Nicolas Bock wrote:
Thanks Thomas for the helpful comments.

It sounds like that there is no solution at the moment through
networkmanager-1.0.2, right? I was naively considering some script in
/etc/NetworkManager/dispatcher.d, but from the email threads you link
it sounds like as if the routing table update would happen anyway.

A dispatcher script would not prevent NM from adding any routes.

Maybe using the VPN, you use it together with a connection
that either only has static configuration
or that suppresses routes from DHCP
that might work well enough, but that's not a real solution.

Could I do that such that nm uses the normal approach while not using
ncsvc, and switches to ignoring routes while under VPN?


Thanks again for the help!


On Thu, Jun 4, 2015 at 5:45 AM, Thomas Haller <thaller redhat com>
On Do, 2015-06-04 at 04:55 -0600, Nicolas Bock wrote:

When I run the Juniper Network Connect client (ncsvc) it
every time the DHCP license is renewed. The log files of ncsvc
unfortunately rather cryptic, but it appears as if the DHCP
leads to a change in the routing table which triggers a
in ncsvc which then tears down the VPN tunnel. Using timestamps
following two events correlate:

20150603133456.514649 ncsvc[p6870.t6870] rmon.error Route to
destination is missing mask with gw, 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
Jun 03 13:34:55.454985 host NetworkManager[1805]: plen 24
Jun 03 13:34:55.454990 host NetworkManager[1805]: expires in 300
Jun 03 13:34:55.455026 host NetworkManager[1805]: gateway
Jun 03 13:34:55.455035 host NetworkManager[1805]: nameserver
Jun 03 13:34:55.455210 host NetworkManager[1805]: (wlp6s0):
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
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
'dhcp4-change' for wlp6s0
Jun 03 13:34:56.514958 host systemd-networkd[1803]: tun0 : lost

Besides the ncsvc error listed above I sometimes also see this

20150603132151.174661 ncsvc[p6870.t6870] rmon.error Unauthorized
route to has been added        (conflicts
our route to, 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:

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.

There was an idea to add a feature to "propert routes".
It's not clear how this feature could look like, but probably it
be designed in a way, that you can tell NM ~not to configure~

IMO ncsvc should allow you to white-list certain routes, so you
say: don't tear down VPN when somebody messes with


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