[riot-devel] Connecting RasPi with RIOT node via 6lowpan using ULAs

Sebastian Meiling meiling.sebastian at gmail.com
Wed Feb 10 21:04:25 CET 2016

Hi all,

I'm having some trouble with a rather simple sensor network application: my goal is to query a sensor node (RIOT) using COAP/UDP over 6lowpan from a RasPi. The Pi is equipped the well known openlabs 802.15.4 transceiver module[1], it runs latest Raspbian Jessie with a self compiled wpan-enabled Linux-Kernel. The sensor node is an Atmel samr21-xpro for my initial tests I installed the gnrc_networking example from latest RIOT master. I setup a lowpan device on the Pi with same channel and pan-id as the RIOT node.

My initial findings:
- ping and data transmission using link local address works fine
- ping and data transmission using ULAs doesn't work in any direction
- setup ULA as follows:
 - RasPi 	`sudo ip addr add fd59:7f5:2065:7622::2/64 dev lowpan0`
 - RIOT-node 	`ifconfig 7 add fd59:7f5:2065:7622:0000:0000:0000:0003`

I enabled some debugging under `sys/net/gnrc/network_layer` in `icmpv6`, `ipv6`, and `ndp` to dig a little deeper. Further I used wireshark+dumpcap on the RasPi to sniff lowpan traffic. My observations for pings RasPi <-> RIOT using ULAs:

1. RIOT -> RasPi:

- no packets get out, so no wireless transmission visible on sniffer
- packet send fails with "ipv6: error determining next hop's link layer address" in gnrc_ipv6.c:_send [2]

2. RasPi -> RIOT:

- sniffer sees neighbor solicitation from RasPi for ULA of RIOT node (fd59:7f5:2065:7622::3)
- RIOT debug messages show:
  - NS is received by RIOT
  - RIOT sets neighbor cache entry for RasPi ULA
  - RIOT assembles neighbor advertisement (NA)
  - send of NA fails as before in [2]
- RasPi cannot resolve ULA, thus ping fail

Has anybody (recently) tried a similar setup using RasPi with lowpan module to connect to a RIOT node? In the RIOT wiki I found an old entry for a RasPi border gateway, this looks quite similar though I don't need the forwarding part (yet). Or asking differently: should ping via ULA work as I would expect or is there any reason that this should not work with 6lowpan. The same setup between e.g. Linux and OS X using ULAs works fine: I know 6lowpan is not IPv6 and vis-versa ...

Thanks in advance for any hint on solving this,


[1]: http://openlabs.co/store/Raspberry-Pi-802.15.4-radio
[2]: https://github.com/RIOT-OS/RIOT/blob/master/sys/net/gnrc/network_layer/ipv6/gnrc_ipv6.c#L627
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