[Battlemesh] routing daemons fighting to enforce sysctl settings

[Daniel Golle]

Hi!

I'm currently helping to switch from some ancient OLSR1-based
hand-crafted and hard-to-maintain firmware to a Libre-Mesh based
environment. In order to integrate with the existing OLSR1 mesh, some
nodes should run BMX6/7 as well as OLSRd (using 2 devices is not an
option, we just don't have enough of them). While this generally works
nicely due to the routing-table-import features of BMX6, there is a
single very annoying problem:
Both routing daemons try changing sysctl settings in conflicting ways
without any means for the user to disable that 'egocentric' behaviour.
olsrd[21487]: Writing '0' (was 2) to /proc/sys/net/ipv4/conf/all/rp_filter
bmx7[1237]: INFO  check_proc_sys_net(): changing /proc/sys/net/ipv4/conf/all/rp_filter from 0 to 2

I generally believe that a routing daemon shouldn't take-over the OS to
a degree which makes co-existence with other routing daemons or other
networking stuff impossible. Currently both, OLSRd and BMX repeatingly
try to enforce settings even in /proc/sys/net/ipv*/conf/all/ which thus
affects all interfaces and not only the ones governed by that specific
protocol.

I had a discussion with Henning about a similar issue I had with OLSRd
changing send_redirects without any way to configure it not to touch
sysctl values. Now the problem came back and kinda confirms my opinion
that setting sysctl options (/proc/sys/net/*) is a task to be carried
out by the OS, ie. netifd on OpenWrt/LEDE or connman or NetworkManager
or whatever-you-use.

Thus my demand to routing protocols developers: Please at least create
a way to tell your routing daemon "don't touch my sysctl, I'll take
care of it myself!". This should imho be the default for the
OpenWrt/LEDE build of the routing daemons and netifd should handle
stuff like rp_filter and send_redirects -- the routing daemon might
still warn you about UCI settings known to cause problems under certain
conditions.



Cheers


Daniel