Recently I have been helping Andy Gelme with a project which uses contiki-os, and 6lowpan on a device called a MeshThing. This required us to setup a small IPv6 network from scratch, independent of the internet, this turned out to be quite a bit different an objective of most of the how to’s we found so I decided to document our method, as much for others as myself.

In our case the network looked as follows:

Simple Network

In this diagram we have macbook A which is connected to a MeshThing running contiki-os connected via serial over USB. The ipv6 connection is provided by slip6, which gives use a point to point link over the serial connection. The command to start tunslip6 is as follows:

sudo ./tunslip6 -B 38400 -s /dev/tty.usbmodem1411 aaaa::1/64
********SLIP started on ``/dev/tty.usbmodem1411''
opened tun device ``/dev/tun0''
ifconfig tun0 inet6 up
ifconfig tun0 inet6 aaaa::1/64 add
sysctl -w net.inet6.ip6.forwarding=1
net.inet6.ip6.forwarding: 1 -> 1
ifconfig tun0

tun0: flags=8851<UP,POINTOPOINT,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	inet6 fe80::bae8:56ff:ffff:ffff%tun0 prefixlen 64 optimistic scopeid 0xc
	inet6 aaaa::1 prefixlen 64 tentative
	nd6 options=1<PERFORMNUD>
	open (pid 51393)
RPL started
Online
*** Address:aaaa::1 => aaaa:0000:0000:0000
Got configuration message of type P
Setting prefix aaaa::
Server IPv6 addresses:
 aaaa::11:22ff:ffff:ffff
 fe80::11:22ff:ffff:ffff

So this command, for those not aware is using my USB serial device, running at 38400 baud to establish a link to the device.

At the end of this command we are providing a prefix of aaaa::1/64, which enables the device to pick it’s own IPv6 address using Stateless Address Autoconfiguration (SLAAC). It is important to note that this means the prefix needs to use a /64 mask.

Now as we can see in our original diagram we now need to route packets between the aaaa::1/64 network assigned to our mesh.

Given we need to enable routing between macbook B and the MeshThing we need the local wireless network to provide an IPv6 prefix for auto configuration of this host.

As macbook B is going to be routing we will get it to advertise our prefix of bbbb::1/64 on the existing wireless lan.

This is done using rtadvd in BSD derivatives, and rdvd on linux. So to get this running on OSX edit your /etc/rtadvd.conf as root, and add the following line.

en1:\
 :addr="bbbb::1":prefixlen#64:

On linux we can use radvd, which can be installed via apt-get on ubuntu. This is configured via /etc/radvd.conf with the equivalent configuration below.

interface eth1 {
  ## (Send advertisement messages to other hosts)
  AdvSendAdvert on;
  ## IPv6 subnet prefix
  prefix bbbb::1::/64 {
    AdvOnLink on;
    AdvAutonomous on;
  };
};

So in this case we are using en1 on macbook A is the wireless interface. We start rtadvd, this will after about 4 seconds send out a route advertisement which will trigger auto-configuration of all hosts on wireless network, therefore providing a prefix to macbook B which it will used by SLAAC to generate an IPv6 address.

To check our configuration worked correctly, first thing you will notice is that all hosts on the lan now have an IPv6 address in the prefix range.

[~]$ ifconfig en0 | grep inet6
	inet6 fe80::bae8:56ff:ffff:ffff%en0 prefixlen 64 scopeid 0x4
	inet6 bbbb::bae8:56ff:ffff:ffff prefixlen 64 autoconf
	inet6 bbbb::615e:319:aaaa:aaaa prefixlen 64 autoconf temporary

So in order these adresses are:

  • Link Local address, these always begin with fe80:: and also includes our MAC address of b8:e8:56:ff:ff:ff.
  • SLAAC address, which is a combination of the prefix and our MAC.
  • One temporary address, which hides the network card address, this is the one that should be “used by applications”, no idea what this means Wireshark says everything on the LAN is using the MAC based IPv6 addresses I need to RTFM (read the fine manual) more.

To see neighbours in OSX you can use ndp, the R flag in the example below indicates which host is a router.

[~]$ ndp -an
Neighbor                        Linklayer Address  Netif Expire    St Flgs Prbs
bbbb::bae8:56ff:ffff:ffff        b8:e8:56:ff:ff:ff     en0 permanent R

On linux the equivalent command is ip -6 neigh show.

So for Linux, IOS and Android this is all we need to do to provide get the routing to work, however on OSX clients we have one additional step.

As OSX doesn’t accept the route advertisements by default, a route solicitation daemon called rtsold needs to be running on all client machines aside from the router. Below is the command I ran on macbook B, note on this machine the wireless adapter was en0.

sudo rtsold en0

Once this is started you should be able to ping the MeshThing from macbook B on the wireless lan.

[~]$ ping6 aaaa::11:22ff:ffff:ffff
PING6(56=40+8+8 bytes) aaaa::1 --> aaaa::11:22ff:ffff:ffff
16 bytes from aaaa::11:22ff:ffff:ffff, icmp_seq=0 hlim=64 time=34.186 ms
16 bytes from aaaa::11:22ff:ffff:ffff, icmp_seq=1 hlim=64 time=33.553 ms
--- aaaa::11:22ff:fe33:4401 ping6 statistics ---
2 packets transmitted, 2 packets received, 0.0% packet loss
round-trip min/avg/max/std-dev = 33.553/33.870/34.186/0.316 ms

This is a part of my ongoing hardware hacking, for more details on how this started see Adding an ICSP header to the ATmega256RFR2 . As a note both my Atmel board and the MeshThing use the ATmega256RFR2 chips.

The next goal is to setup some name services, probably via MDNS, and test accessing the web site (yes on the 8 bit micro controller) from a mobile phone connected to the wireless network.

Update

Need to look into using site-local addresses in the fc00::/7 block rather than unallocated public space, as recommended by Julien Goodwin see unique local addresses.


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