SLIP is the “mostly obsolete” wikipedia:Serial Line Internet Protocol. “On personal computers, SLIP has been largely replaced by the Point-to-Point Protocol (PPP), which is better engineered, has more features and does not require its IP address configuration to be set before it is established. On microcontrollers, however, SLIP is still the preferred way of encapsulating IP packets due to its very small overhead.”

Contiki uses SLIP to bridge the wireless IPv6 network onto a PC via a USB connection. So with your Zigduino plugged into your PC, and the right software running on each, traffic from the wireless IP network can reach your site-wide Ethernet network and potentially beyond.

On Zigduino, there is only one UART exposed. This means we have to choose between reading debug messages and connecting to our PC via SLIP. This change is exposed by adding “WITH_SLIP=1” to the makefile or command line for any particular project. Projects made “WITH_SLIP” will expect to talk to a slip tunnel on the PC side.

Speaking of the PC side… In order for SLIP to work, something on the host PC has to be listening. Using Instant Contiki, the 'tunslip6' will do this. Running it in Linux creates a 'tun0' interface which gives the connected Zigduino an address of aaaa::1 on your local network.

First, built the tunslip6 tool. This works without modification on Instant Contiki.

 
$ cd tools 
$ make tunslip6 

Now make and upload the border router itself. Be sure to include “WITH_SLIP=1” to turn on slip for this node, and “WITH_WEBSERVER=0” to exclude a web server from this node.

 
$ cd examples/ipv6/rpl-border-router 
$ make TARGET=avr-zigduino savetarget 
$ make WITH_SLIP=1 WITH_WEBSERVER=0 -j10 
$ make upload AVRDUDE_PORT=/dev/ttyUSB0 

Ok, now it's built. Let's bring up the slip interface on Linux. Note that the baud rate here has to match the baud rate in the uart setup on the board, which is currently 38400. That's a little slow, but I'll work on bringing it up in future revisions. Also note the “v6” switch. That turns on maximum debugging output so we can follow along.

$ sudo ../../../tools/tunslip6 aaaa::1/64 -s /dev/ttyUSB0 -B 38400 -v6 
********SLIP started on ``/dev/ttyUSB0 opened tun device ``/dev/tun0 
ifconfig tun0 inet `hostname` up 
ifconfig tun0 add aaaa::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:127.0.1.1  P-t-P:127.0.1.1  Mask:255.255.255.255           
     inet6 addr: aaaa::1/64 Scope:Global           
     UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1500  Metric:1           
     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) 
tun0 Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00             
     inet addr:127.0.0.1  P-t-P:127.0.0.1  Mask:255.255.255.255           
     inet6 addr: aaaa::1/64 Scope:Global           
     UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1500  Metric:1           
     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) 
IP addresses [4 max] fdfd::3 fe80::11:22ff:fe33:4403 RPL-Border router started 
*** Address:aaaa::1 => aaaa:0000:0000:0000 SIN: 10 Got configuration message of type P 
Setting prefix aaaa:: created a new RPL dag Server IPv6 addresses:  aaaa::11:22ff:fe33:4403  
fdfd::3  fe80::11:22ff:fe33:4403 

It's helpful that tunslip6 is putting through the debug messages from the Zigduino. So we can see the boot-up process complete successfully.

We should now be able to ping the border router from the host PC. First, we can ping its auto-configured aaaa::/64 address

$ ping6 aaaa::11:22ff:fe33:4403 
PING aaaa::11:22ff:fe33:4403(aaaa::11:22ff:fe33:4403) 56 data bytes 
64 bytes from aaaa::11:22ff:fe33:4403: icmp_seq=1 ttl=64 time=66.1 ms 
64 bytes from aaaa::11:22ff:fe33:4403: icmp_seq=2 ttl=64 time=68.6 ms 
64 bytes from aaaa::11:22ff:fe33:4403: icmp_seq=3 ttl=64 time=66.2 ms

We want to reach more nodes than just the one connected. So let's add a route on the host PC. This “route add” command tells Ubuntu that whenever it wants to reach a node whose IP starts with fdfd::/64, it can send that through the tun0 interface.

 
$ sudo route -A inet6 add fdfd::/64 dev tun0 
$ netstat -r6 Kernel IPv6 routing table 
Destination                    Next Hop                   Flag Met Ref Use If 
aaaa::/64                      ::                         U    256 0     0 tun0 
fdfd::/64                      ::                         U    1   0     0 tun0 

Now that we have the route set up, we can put another node on the network, and ping that.

Put anything that speaks RPL on fdfd::1, for example rpl-collect/sender

$ cd examples/ipv6/rpl-collect 
$ make TARGET=avr-zigduino savetarget 
$ make udp-sender.avr-zigduino.u AVRDUDE_PORT=/dev/ttyUSB1 -j10 

Now see that we can ping it ok:

$ ping6 fdfd::1 PING fdfd::1(fdfd::1) 56 data bytes 
64 bytes from fdfd::1: icmp_seq=1 ttl=64 time=67.8 ms 
64 bytes from fdfd::1: icmp_seq=2 ttl=64 time=66.3 ms