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

smlng s at mlng.net
Fri Apr 22 12:19:36 CEST 2016

Hi everyone,

I'm testing COAP between RIOT on Phytec pba-d-01-kw2x and Linux on RasPi+Openlabs using ULA IP addresses. 

On the Pi I run a 'radvd' to advertise a ULA prefix to RIOT, which works:
 - RIOT sends RS after boot
 - the Pi answers with RA containing ULA prefix
 - RIOT configures ULA IP on 6lo iface

COAP (or communication in general) via ULA IP works, as long as RIOT has the Pi in its routers cache. However, sometimes RIOT _forgets_ or does not set a routers entry for the Pi at all. In that case communication is not possible via ULAs, using link-local IPs works all the time. The issue seems be with the RS+RA processing. I found that sometimes RIOT does not create a routers entry on reception of a RA - though it does configure the ULA prefix correctly. 

I just had the case that RIOT configures the ULA _and_ sets a routers entry, hence communication was working. At least for about 15min, but then RIOT send another RS, Pi answers with RA, RIOT still has ULA IP configured -- BUT the routers entry for the Pi is gone and communication fails. Again: using link-local IPs still works.

Btw. even when communication via ULAs is working, RIOT never creates a ncache entry for ULA IP of the Pi but it did create an ncache entry for link-local IP of the Pi. I thought the latter is not required/allowed in 6lo but for ULAs it should create an entry?

Has somebody else observed this behavior or any hints how to resolve this?

Thanks, best

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