MQTT-SN with public IPv6 network and A8-M3 nodes

Difficulty: High Duration: 45 minutes

Prerequisites: Configure SSH Access , RIOT basics

Description: The goal of this tutorial is to discover the MQTT procotol and its contrained variant called MQTT-SN with RIOT on IoT-LAB. You will reserve 3 A8 nodes on the Saclay site, build and flash the required firmwares on the A8-M3 nodes, create a simple IPv6 network in IoT-LAB. Finally, from the saclay SSH frontend host, you’ll publish MQTT messages to the test/riot topic. The messages will be displayed by the MQTT-SN client running on the RIOT node. The first node will be used as a border router for propagating an IPv6 prefix through its wireless interface, the second node will be used a as MQTT broker (using the mosquitto.rsmb application) and the third node will run a RIOT application containing a shell and a MQTT-SN client to connect to the brober.

Connect to Saclay SSH frontend:

my_computer$ ssh <login>@saclay.iot-lab.info

Start an experiment called riot_ipv6_a8 that contains 2 A8 nodes.
```
login@saclay:~$ iotlab-auth -u <login> 
login@saclay:~$ iotlab-experiment submit -n riot_a8 -d 60 -l 2,archi=a8:at86rf231+site=saclay
```
Remember the experiment identifier returned by the last command. It’ll be used in the commands shown below, <exp_id>. The requested experiment duration is 60 minutes.

Wait a moment until all nodes are up:

  login@saclay:~$ iotlab-ssh --verbose wait-for-boot

Wait a moment until the experiment is launched (state is Running) and get the nodes list. For the next of this tutorial we suppose that you obtained a8-1.saclay.iot-lab.info and a8-2.saclay.iot-lab.info nodes.
```
login@saclay:~$ iotlab-experiment get -i <exp_id> -p
login@saclay:~$ iotlab-experiment get -i <exp_id> -n
```
Get the code of the 2020.10 release of RIOT from GitHub:
```
login@saclay:~$ mkdir -p ~/A8/riot
login@saclay:~$ cd ~/A8/riot
login@saclay:~/A8/riot$ git clone https://github.com/RIOT-OS/RIOT.git -b 2020.10-branch
login@saclay:~/A8/riot$ cd RIOT
```
Note that you can also use the RIOT development code (e.g the master branch) at your own risk : this tutorial may not fully work.

Important note: to minimize radio interferences with other experiments you can build the firmwares below to make them use a different 802.15.4 channel (default is 26).
To do so, add DEFAULT_CHANNEL=<channel> option to the make commands.

Build the required firmware for the border router node. The node node-a8-1 will act as the border router in this experiment. The border firmware is built using the RIOT gnrc_border_router example

login@saclay:~/A8/riot/RIOT$ source /opt/riot.source
login@saclay:~/A8/riot/RIOT$ make ETHOS_BAUDRATE=500000 DEFAULT_CHANNEL=<channel> BOARD=iotlab-a8-m3 -C examples/gnrc_border_router clean all
login@saclay:~/A8/riot/RIOT$ cp examples/gnrc_border_router/bin/iotlab-a8-m3/gnrc_border_router.elf ~/A8/.

Build the required firmware for the other node. RIOT gnrc_networking example will be used for this purpose.

login@saclay:~/A8/riot/RIOT$ make DEFAULT_CHANNEL=<channel> BOARD=iotlab-a8-m3 -C examples/gnrc_networking clean all
login@saclay:~/A8/riot/RIOT$ cp examples/gnrc_networking/bin/iotlab-a8-m3/gnrc_networking.elf ~/A8/

Connect to the A8 of the M3 border router: node-a8-1.

login@saclay:~$ ssh root@node-a8-1

Then flash the BR firmware on the M3 and build the required RIOT configuration tools: uhcpd (Micro Host Configuration Protocol) and ethos (Ethernet Over Serial).

root@node-a8-1:~# iotlab_flash A8/gnrc_border_router.elf
root@node-a8-1:~# cd ~/A8/riot/RIOT/dist/tools/uhcpd 
root@node-a8-1:~/A8/riot/RIOT/dist/tools/uhcpd# make clean all
root@node-a8-1:~/A8/riot/RIOT/dist/tools/uhcpd# cd ../ethos
root@node-a8-1:~/A8/riot/RIOT/dist/tools/ethos# make clean all

On the border router, the network can finally be configured automatically using the following commands:

root@node-a8-1:~/A8/riot/RIOT/dist/tools/ethos# ./start_network.sh /dev/ttyA8_M3 tap0 2001:660:3207:401::/64 500000
net.ipv6.conf.tap0.forwarding = 1
net.ipv6.conf.tap0.accept_ra = 0
----> ethos: sending hello.
----> ethos: activating serial pass through.
----> ethos: hello reply received

Note that we propagate another subnetwork for the border router (M3 node) in our LLN, 2001:660:3207:401::/64. You can find informations about IPv6 subnetting for A8-M3 nodes here. You can also get this prefix directly on the A8 node:

root@node-a8-1:~# printenv
INET6_PREFIX_LEN=64
INET6_PREFIX=2001:0660:3207:401
INET6_ADDR=2001:0660:3207:0400::1/64

Now, in another terminal, log on the remaining A8 node, node-a8-2. We are going to configure and start the MQTT-SN broker as follows:

my_computer$ ssh <login>@saclay.iot-lab.info
login@saclay:~$ ssh root@node-a8-2

Edit a file config.conf (vim config.conf) with the following content:

# add some debug output
trace_output protocol
   
# listen for MQTT-SN traffic on UDP port 1885
listener 1885 INADDR_ANY mqtts
  ipv6 true
   
# listen to MQTT connections on tcp port 1886
listener 1886 INADDR_ANY
  ipv6 true

Important, note the global IPv6 address of this node, since we’ll use it to connect to the MQTT broker from the node:

root@node-a8-2:~# ip -6 -o addr show eth0
2: eth0    inet6 2001:660:3207:400::66/64 scope global        valid_lft forever preferred_lft forever
2: eth0    inet6 fe80::fadc:7aff:fe01:98fc/64 scope link        valid_lft forever preferred_lft forever

And finally start the broker:

root@node-a8-2:~# broker_mqtts config.conf
20170715 001526.077 CWNAN9999I Really Small Message Broker
20170715 001526.084 CWNAN9998I Part of Project Mosquitto in Eclipse
(http://projects.eclipse.org/projects/technology.mosquitto)
20170715 001526.088 CWNAN0049I Configuration file name is config.conf
20170715 001526.099 CWNAN0053I Version 1.3.0.2, Jul 11 2017 14:55:20
20170715 001526.102 CWNAN0054I Features included: bridge MQTTS 
20170715 001526.104 CWNAN9993I Authors: Ian Craggs (icraggs@uk.ibm.com), Nicholas O'Leary
20170715 001526.111 CWNAN0300I MQTT-S protocol starting, listening on port 1885
20170715 001526.115 CWNAN0014I MQTT protocol starting, listening on port 1886

You now have a running MQTT/MQTT-SN broker running on node-a8-2.

This broker is reachable :

from the SSH frontend using MQTT on port 1886
from any M3 nodes behind the border router using MQTT-SN on port 1885 (in our case, node-a8-3, see below)

Finally, in a third terminal, log on the SSH frontend, build and flash the RIOT MQTT-SN example firmware on the M3:

   my_computer$ ssh <login>@saclay.iot-lab.info
   login@saclay:~$ source /opt/riot.source
   login@saclay:~$ cd ~/A8/riot/RIOT
   login@saclay:~/A8/riot/RIOT$ make BOARD=iotlab-a8-m3 -C examples/emcute_mqttsn
   login@saclay:~/A8/riot/RIOT$ iotlab-ssh flash-m3 examples/emcute_mqttsn/bin/iotlab-a8-m3/emcute_mqttsn.elf -l saclay,a8,3

You can now login to the A8 and connect to the M3 via the serial port to access the RIOT shell:

   login@saclay:~$ ssh root@node-a8-3
   root@node-a8-2:~# miniterm.py /dev/ttyA8_M3 500000 -e
   > help
   Command        
     Description
   ---------------------------------------
   con                  connect to MQTT broker
   discon               disconnect from the current broker
   pub                  publish something
   sub                  subscribe topic
   unsub                unsubscribe from topic
   will                 register a last will
   reboot               Reboot the node
   ps                   Prints information about running threads.
   ping6                Ping via ICMPv6
   random_init          initializes the PRNG
   random_get           returns 32 bit of pseudo randomness
   ifconfig             Configure network interfaces
   ncache               manage neighbor cache by hand
   routers              IPv6 default router list

Use the con command to connect to the MQTT-SN broker on node-a8-2 and subscribe to the test/riot topic using the sub command.

   > con 2001:660:3207:400::66 1885
   > sub test/riot

In a fourth terminal, connect to the SSH frontend and use the preinstalled mosquitto client CLI to publish and subscribe to topics on the MQTT broker running on node-a8-2
```
   login@saclay:~$ mosquitto_pub -h 2001:660:3207:400::66 -p 1886 -t test/riot -m iotlab
```
On the RIOT shell (node-a8-3, third terminal), you get the following message:
```
   ### got publication for topic 'test/riot' [1] ###
   iotlab
```

If everything works as described, you are able to use MQTT-SN with RIOT on IoT-LAB. Congratulations !
Now play with mosquitto_sub on the frontend side (fourth terminal) and the pub command in the RIOT node shell (third terminal) to exchange messages from the node to the frontend.