[riot-devel] RIOT+ULAs: no router entry

Alexander Aring alex.aring at gmail.com
Fri Apr 29 17:25:03 CEST 2016

On Fri, Apr 29, 2016 at 04:58:04PM +0200, smlng wrote:
> Hi Alex,
> hi all,
> over the last days I did some more extensive tests and enabled/added some debug output in RIOT, and I got close to the root cause of the problem. 
> TL;DR: 
> - Linux does not set the router flag in its NAs
> - but it should when `radvd` is running (or `radvd` should enable it). 
> - RIOT behaves correctly, according to RFC-4861 7.2.4.
> ----
> Now the slightly longer version; I quickly recap my setup:
> - a RasPi with OpenLabs transceiver, and `radvd` (linux-wpan version from github)
> - Atmel samr21-xpro running RIOT with `gnrc_networking` example (2016.04-branch)
> - `radvd` announces a ULA-prefix (though ULA doesn't matter, could global as well)
> I observed the following behavior:
> - RIOT send RS on boot, `radvd` on RasPi replies with RA (incl. PIO, ABRO, SLLAO)
> - RIOT parse RA, generates IP from prefix, adds NCE for router with router flag set
> - RIOT send NS for RasPi/routers link-local address -> RasPi replies with NA
> - RIOT parses NA, but router flag not set -> unset router flag in NCE of router
> - hence no more router in cache -> no ping or data transfer via non-link-local (e.g. ULA) IPs 
> so my question @alex and @linux-wpan: can I manually set/enable the routers flag for NAs in Linux Kernel? Or somehow _convince_ `radvd` to do so on startup?

Routers are indicated by the "forwarding" setting. radvd silent warns
about that if this isn't set for interfaces with RA advert is on, so far I
know you need to increase the debug level for that.

I simple set:

echo 1 > /proc/sys/net/ipv6/conf/all/forwarding

this will set forwarding for all interfaces.

Some code explaining:

See http://lxr.free-electrons.com/source/net/ipv6/ndisc.c#L838

this is at function when NS is received, the routeri flag will be set when
forwarding is enabled.

Maybe this solves all your current issues. :-)

> I'm running latest Raspbian with Kernel 'Linux raspberrypi 4.1.19+' and wpan-tools from github on the RasPi.

I would better use bluetooth-next, if possible. With all recent patches
you could also try to use 6CO in radvd.

btw: the radvd wants to accept my patches for 6lowpan 6CO stuff, but
basic 6LoWPAN-ND (first short address support for NA/NS) will be added
and short-address handling will not work with RIOT, but that's another

- Alex

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