Public IPv6 (6LoWPAN/RPL) network with M3 nodes

Difficulty: Medium Duration: 45 minutes

Prerequisites: Configure SSH Access , RIOT basics

Description: The goal of this tutorial is to discover the basics of RIOT GNRC stack & tools for IoT-LAB IPv6. You will reserve 2 M3 nodes on the Saclay site, build 2 firmwares and flash them on the M3 nodes, and create a simple IPv6 network in IoT-LAB. Finally, you’ll access nodes using UDP over IPv6 from the SSH frontend (or any Host with a global IPv6 address), using the ethos_uhcpd.py tool provided on the frontend.

Connect to Saclay site host:

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

Start an experiment with 2 M3 nodes called riot_m3:
```
  login@saclay:~$ iotlab-auth -u <login>
  login@saclay:~$ iotlab-experiment submit -n riot_m3 -d 60 -l 2,archi=m3: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 the experiment is launched (state is Running) and get the nodes list. For the next of this tutorial we suppose that you obtained m3-1.saclay.iot-lab.info and m3-2.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 ~/riot
login@saclay:~$ cd ~/riot
login@saclay:~/riot$ git clone https://github.com/RIOT-OS/RIOT.git -b 2020.10-branch
login@saclay:~/riot$ cd RIOT
```
Note: you can also use the RIOT development code (e.g the master branch) but this will be at your own risk: this tutorial may not fully work.
Build the required firmware for the border router node. The node m3-1 will act as the border router in this experiment. The border firmware is built using the RIOT gnrc_border_router example.

Important note 1: we build this firmware with a baudrate of 500000. This is mandatory for ethos_uhcpd.py script to work effectively since the UART baudrate of the M3 is 500000.

Important note 2: to minimize radio interferences with other users experiments, the firmwares used can be built for different 802.15.4 channel (default is 26, allowed values goes from 11 to 26).
To do this, add DEFAULT_CHANNEL=<channel> option to the make commands.
```
login@saclay:~/riot/RIOT/$ source /opt/riot.source
login@saclay:~/riot/RIOT/$ make ETHOS_BAUDRATE=500000 DEFAULT_CHANNEL=<channel> BOARD=iotlab-m3 -C examples/gnrc_border_router clean all
```
Use the CLI-Tools to flash the gnrc_border_router firmware that you have just built on the first M3 node. Here we use m3-1 but it may change in your case:
```
login>@saclay:~/riot/RIOT/$ iotlab-node --flash examples/gnrc_border_router/bin/iotlab-m3/gnrc_border_router.elf -l saclay,m3,1
```
Now you can configure the network of the border router on m3-1 and propagate an IPv6 prefix with ethos_uhcpd.py.
```
login@saclay:~$ sudo ethos_uhcpd.py m3-1 tap0 2001:660:3207:04c1::1/64
```
The network is finally configured:
```
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, 2001:660:3207:04c1::/64. You can find informations about IPv6 subnetting for M3 nodes here.
- Note 1: leave the terminal open (you don’t want to kill ethos_uhcpd.py, it bridges the BR to the front-end network)
- Note 2: If you have an error “Invalid prefix – Network overlapping with routes”, it’s because another experiment is using the same ipv6 prefix (e.g. 2001:660:3207:04c1::/64).
  
  You can view currently used IPv6 prefixes on the frontend SSH with this command:
```
 login@saclay:~$ ip -6 route
 2001:660:3207:4bf::/64 dev eth0  proto kernel  metric 256 
 2001:660:3207:4c1::/64 via fe80::2 dev tap0  metric 1024 
 fe80::/64 dev eth1  proto kernel  metric 256 
 fe80::/64 dev eth0  proto kernel  metric 256 
 fe80::/64 dev tap0  proto kernel  metric 256 
 default via 2001:660:3207:4bf:ff:: dev eth0  metric 1024
```
- Note 3: If you have an error “Device or resource busy”, it’s because another user is using the same tap interface (e.g. tap0). Just use another one.
  You can view currently used tap interfaces using the same command than in the previous note.

Now, in another terminal, SSH to the SSH frontend and build the required firmware for the other node. RIOT gnrc_networking example will be used for this purpose.

login@saclay:~$ cd riot/RIOT
login@saclay:~/riot/RIOT/$ source /opt/riot.source
login@saclay:~/riot/RIOT/$ make DEFAULT_CHANNEL=<channel> BOARD=iotlab-m3 -C examples/gnrc_networking clean all

Use the CLI-Tools to flash the gnrc_networking firmware that you have just built on the first M3 node. Here we use m3-2 but it may change in your case:

login@saclay:~/riot/RIOT/$ iotlab-node --flash examples/gnrc_networking/bin/iotlab-m3/gnrc_networking.elf -l saclay,m3,2

You can now interact with the second M3 node. m3-2 using nc.

my_computer$ ssh <login>@saclay.iot-lab.info
login@saclay:~$ nc m3-2 20000

You now have access to the RIOT shell and can ping another Internet host using IPv6 (let’s try a Google DNS host):

> help
> ping6 2001:4860:4860::8888
ping6 2001:4860:4860::8888
12 bytes from 2001:4860:4860::8888: id=83 seq=1 hop limit=50 time = 36.113 ms
12 bytes from 2001:4860:4860::8888: id=83 seq=2 hop limit=50 time = 34.839 ms
12 bytes from 2001:4860:4860::8888: id=83 seq=3 hop limit=50 time = 36.918 ms
--- 2001:4860:4860::8888 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2.06113456 s
rtt min/avg/max = 34.839/35.956/36.918 ms

Use RIOT shell ifconfig command to get the IP of the M3 node:

> ifconfig
Iface  7   HWaddr: 29:02  Channel: 26  Page: 0  NID: 0x23
        Long HWaddr: 36:32:48:33:46:df:a9:02 
        TX-Power: 0dBm  State: IDLE  max. Retrans.: 3  CSMA Retries: 4 
        AUTOACK  CSMA  MTU:1280  HL:64  6LO  RTR  RTR_ADV  IPHC  
        Source address length: 8
        Link type: wireless
        inet6 addr: ff02::1/128  scope: local [multicast]
        inet6 addr: fe80::1711:6b10:65fd:bd36/64  scope: local
        inet6 addr: ff02::1:fffd:bd36/128  scope: local [multicast]
        inet6 addr: 2001:660:3207:4c1:1711:6b10:65fd:bd36/64  scope: global
        inet6 addr: ff02::2/128  scope: local [multicast]

The global prefix has been successfully propagated, the IP on the M3 is 2001:660:3207:4c1:1711:6b10:65fd:bd36. Verify that it answers to “ping” from the SSH frontend (and from any computer with a global IPv6):

login@saclay:~$ ping6 -c 3 2001:660:3207:4c1:1711:6b10:65fd:bd36
PING 2001:660:3207:4c1:1711:6b10:65fd:bd36(2001:660:3207:4c1:1711:6b10:65fd:bd36) 56 data bytes
64 bytes from 2001:660:3207:4c1:1711:6b10:65fd:bd36: icmp_seq=1 ttl=61 time=45.7 ms
64 bytes from 2001:660:3207:4c1:1711:6b10:65fd:bd36: icmp_seq=2 ttl=61 time=46.5 ms
64 bytes from 2001:660:3207:4c1:1711:6b10:65fd:bd36: icmp_seq=3 ttl=61 time=44.9 ms
   
--- 2001:660:3207:4c1:1711:6b10:65fd:bd36 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 44.919/45.759/46.595/0.684 ms

Still on m3-2, let’s verify that UDP packets can be received from the SSH frontend. Use the udp command in the gnrc_networking shell to start an UDP server on the M3 node:

> udp server start 8888
udp server start 8888
Success: started UDP server on port 8888

Then from the SSH frontend, send a message by udp:

login@saclay:~$ echo "hello" > /dev/udp/2001:660:3207:4c1:1711:6b10:65fd:bd36/8888

Verify that the packet is received by the M3 node:

> PKTDUMP: data received:
~~ SNIP  0 - size:   5 byte, type: NETTYPE_UNDEF (0)
000000 68 65 6c 6c 6f
~~ SNIP  1 - size:   8 byte, type: NETTYPE_UDP (4)
   src-port: 49568  dst-port:  8888
   length: 13  cksum: 0x45fb6
~~ SNIP  2 - size:  40 byte, type: NETTYPE_IPV6 (2)
traffic class: 0x00 (ECN: 0x0, DSCP: 0x00)
flow label: 0x92520
length: 13  next header: 17  hop limit: 52
source address: 2001:660:3207:4bf::17
destination address: 2001:660:3207:4c1:1711:6b10:65fd:bd36
~~ SNIP  3 - size:  24 byte, type: NETTYPE_NETIF (-1)
if_pid: 7  rssi: 18  lqi: 255
src_l2addr: 36:32:48:33:46:d4:9a:22
dst_l2addr: 36:32:48:33:46:df:a9:02
~~ PKT    -  4 snips, total size:  77 byte

If everything works as described, the Border Router is correctly configured. Congratulations !