RPL Border Router

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Border routers are routers that can be found at the edge of a network. Their function is to connect one network to another. In this tutorial we will learn how to run a simulation using the border router in Contiki 2.7. In the example which we will discuss in the rest of this tutorial the border router will be used to route data between a WSN (RPL network) and an external IP network.



The objective of this tutorial is to give you an understanding of the RPL Border Router code in Contiki 2.7 OS and learn how to simulate a network with a border router on Cooja

At the end of the tutorial you would have learnt the following:

1. Understanding the working of the rpl border router code
2. Starting a simulation on Cooja simulator.
3. Observing and validating the results

Code building blocks.

We will be using the following files

1. border-router.c
2. udp-server.c (udp-client.c can also be used)
3. slip-bridge.c (It contains callback function for processing a SLIP connection request)
4. httpd-simple.c (A simple web server forwarding page generation to a protothread)

udp-server nodes will form a DAG with the border router set as the root. The border router will receive the prefix through a [SLIP][1] (Serial Line Interface Protocol) connection and it will be communicated to the rest of the nodes in the RPL network.

Refer to the following code snippets in the file border-router.c In this piece of code the node configured as the border router waits for the prefix to be set. Once it receives the prefix, the border router is set as the root of the DAG after which it sets the prefix of the rest of the nodes in the network.

/* Request prefix until it has been received */ 
 while(!prefix_set) { 
   etimer_set(&et, CLOCK_SECOND); 

 dag = rpl_set_root(RPL_DEFAULT_INSTANCE,(uip_ip6addr_t *)dag_id); 
 if(dag != NULL) { 
   rpl_set_prefix(dag, &prefix, 64); 
   PRINTF("created a new RPL dag\n"); 

By default the border router hosts a simple web page. However, this can be disabled by defining WEBSERVER as seen the code snippet below. This webpage is displayed when the IPv6 address of the border router is entered in the browser. Refer to the file httpd-simple.c for the following code snippet

PROCESS(border_router_process, "Border router process");
/* No webserver */
/* Use an external webserver application */
#include "webserver-nogui.h"

Compiling the code

The code for RPL border router can be found at /contiki-2.7/examples/ipv6/rpl-border-router. Use the following command to compile the code for the border router

cd /contiki-2.7/examples/ipv6/rpl-border-router 
make TARGET=sky. 

Once this command has been successfully executed, a file named border-router.sky will be created. This file will be used to program one of the motes as the border router on Cooja. For the purpose of this tutorial we will select TMote Sky as our target.

In order to demonstrate the functionality of the border router we will create a network of nodes with the border router as the root. For creating such a network we will user the udp-server.c code. This code can be found at /contiki-2.7/examples/ipv6/rpl-udp . Use the following command to compile the code for rpl-udp

cd /contiki-2.7/examples/ipv6/rpl-udp 
make TARGET=sky 

Once this command has been successfully executed a file named udp-server.sky will be created. This file will be used to program the remaining nodes in Cooja simulator. These nodes will form a DAG with the rpl border router as the root.

Testing on Cooja

Upon the successful completion of the above mentioned steps we are ready to create a simulation in Cooja. Start the Cooja simulator using the following command

cd /contiki-2.7/tools/cooja 
ant run

When the GUI launches execute the following steps to create a simulation.

1. From 'File' select 'New Simulation'. Select 'UDGM', enter the name of the simulation and click on 'create'.
2. Click on 'Motes'. From the drop down menu select 'Add New Motes' followed by 'Create new motes' and select the mote type as 'Sky'.
3. Browse to the location '/contiki-2.7/examples/ipv6/rpl-border-router' and select the file rpl-border-router.sky. Click on 'Create'. Add one mote of this type.
4. Repeat step 2 and 3 but this time browse to the location /contiki-2.7/examples/ipv6/rpl-udp' and select the file udp-server.sky. Add 3 - 4 motes of the type udp-server
5. Once the motes have been added you can position the motes.

Cooja motes.png

Select the options under View as shown below. These will help you creating a topology of your choice.

Motes view.png

6. Now, we need to create a bridge between the RPL network simulated on Cooja and the local machine. This can be done by right clicking on the mote which is programmed as the border router. Select 'More tools for border router' and then select 'Serial Socket (SERVER)'. You will get the following message on the successful completion of this step.Note that the message says 'Listening on port 60001'

Serial Socket.png

7. Now start the simulation by clicking on Start

Tunslip utility

As mentioned in the introduction a border router helps in connecting one network to another. In this example the border router is used to route data between an RPL network and an external network. Till now we have only created the RPL network. Now we need to simulate the scenario in which this RPL network is connected to an external network. For this purpose we will use the Tunslip utility provided in Contiki. In this example tunslip creates a bridge between the RPL network and the local machine. tunslip6.c can be found in /contiki-2.7/tools Compile the tunslip6 code.

make tunslip6 

Make a connection between the RPL network and your local machine.

sudo ./tunslip6 -a aaaa::1/64

On the successful execution this command the following output will be printed on the terminal.

slip connected to ``''
opened tun device ``/dev/tun0''
ifconfig tun0 inet `hostname` up
ifconfig tun0 add aaaa::1/64
ifconfig tun0 add fe80::0:0:0:1/64
ifconfig tun0

tun0      Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  
          inet addr:  P-t-P:  Mask:
          inet6 addr: fe80::1/64 Scope:Link
          inet6 addr: aaaa::1/64 Scope:Global
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:500 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

Rime started with address
MAC 00:12:74:01:00:01:01:01 Contiki 2.7 started. Node id is set to 1.
CSMA ContikiMAC, channel check rate 8 Hz, radio channel 26
Tentative link-local IPv6 address fe80:0000:0000:0000:0212:7401:0001:0101
Starting 'Border router process' 'Web server'
*** Address:aaaa::1 => aaaa:0000:0000:0000
Got configuration message of type P
Setting prefix aaaa::
Server IPv6 addresses:

Go back to the Cooja simulator GUI and look at the dialogue box. The message has now changed to 'Client connected: /'
Client Connected.png

Verifying Results

You can verify that the address of the border router has been set by using the ping command.

user@instant-contiki:~/contiki-2.7$ ping6 aaaa::212:7401:1:101
PING aaaa::212:7401:1:101(aaaa::212:7401:1:101) 56 data bytes
64 bytes from aaaa::212:7401:1:101: icmp_seq=1 ttl=64 time=86.0 ms
64 bytes from aaaa::212:7401:1:101: icmp_seq=2 ttl=64 time=33.6 ms
64 bytes from aaaa::212:7401:1:101: icmp_seq=3 ttl=64 time=82.3 ms
64 bytes from aaaa::212:7401:1:101: icmp_seq=4 ttl=64 time=43.3 ms
64 bytes from aaaa::212:7401:1:101: icmp_seq=5 ttl=64 time=70.1 ms
--- aaaa::212:7401:1:101 ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4006ms
rtt min/avg/max/mdev = 33.669/63.090/86.015/20.985 ms

You can also ping one of the other nodes in the network. Here we are pinging node 4

 user@instant-contiki:~/contiki-2.7$ ping6 aaaa::212:7404:4:404
PING aaaa::212:7404:4:404(aaaa::212:7404:4:404) 56 data bytes
64 bytes from aaaa::212:7404:4:404: icmp_seq=1 ttl=63 time=670 ms
64 bytes from aaaa::212:7404:4:404: icmp_seq=2 ttl=63 time=703 ms
64 bytes from aaaa::212:7404:4:404: icmp_seq=3 ttl=63 time=746 ms
64 bytes from aaaa::212:7404:4:404: icmp_seq=4 ttl=63 time=674 ms
--- aaaa::212:7404:4:404 ping statistics ---
5 packets transmitted, 4 received, 20% packet loss, time 4001ms
rtt min/avg/max/mdev = 670.230/698.666/746.619/30.514 ms

The IPv6 address of a node can be checked from the log screen on Cooja. Filter the nodes by their ID
Node Address.png

You can enter the address of the border router in the web browser. The border router hosts a page which will be displayed on the browser as shown below.
RPL Browser.png

Common Issues

1. Make sure that you enter the IPv6 address properly in the command sudo ./tunslip6 -a aaaa::1/64 . There should be no spaces in aaaa::1/64. Otherwise the code will give unexpected behavior.
2. When you pause the simulation the SLIP connection is lost. It might not work properly on resuming the simulation. In such cases reload the simulation. Create a fresh SLIP connection and then run the simulation again.


[2] https://github.com/njh/contiki/blob/master/cpu/mc1322x/doc/rpl-tutorial.md
[3] Using the Contiki Cooja Simulator - Anuj Sehgal

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