[Olsr-dev] OLSRd IPv6 Mesh @ 25c3

[Jo-Philipp Wich]

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Hi list,

I just wanted to share our success story with olsrd in a pure IPv6 mesh at 25c3.

This year's Freifunk experiment at the Chaos Communication Congress was about building a
pure IPv6 based OLSR mesh and using SIIT translation technique [1] to transport IPv4
traffic via the IPv6 mesh without using tunnels or similar encapsulation techniques.

We had a small mesh of 15-20 nodes up and running at the congress [2]. Some nodes operated
in 802.11g / channel 1, some in 802.11a / channel 100, 2.4GHz and 5GHz clouds where
interconnected using Alix-Boards with two radio interfaces.

The interface IPv6 addresses were composed of a common 64bit prefix
(fdca:ffee:babe:dada::/64) and the upper 64bit of the wifi interface's link local address
(fe80::/64). A sample configuration can be found at [3]

When the experiment started we used the most recent OLSRd release, v0.5.6-r3 running on
top of OpenWrt Kamikaze which worked surprisingly well :) [4]

On several nodes we observed a "slow-start" problem with OLSRd v0.5.6-r3, when a node (or
it's OLSRd instance) was restarted, it took several minutes to re-aquire neighbour routes.
The node successfully received hellos from it's neighbours but the neighbour connections
were stuck with LQ >> 0 and NLQ = 0 for a long time and then suddenly changed the ETX from
INFINITE to near 1.0. Aaron suggested to try again with a more recent version (the hg tip
from 2008/12/29).

So we compiled a more recent version, applied a patch from this list [5] and installed it
on one of the Mesh nodes and gave it a try only to discover that our previously used
configuration file wasn't accepted anymore. A quick run with debug level 1 revealed that
the options "LinkQualityWinSize", "LinkQualityLevel" and "UseHysteresis" weren't supported
anymore, so we just removed them from our configuration.

After the deprecated config options were removed, another proplem arised, olsrd reported
that it can't find the IPv6 address of the interface. After looking at the code changes we
figured out that new options for "Ip6AddrType" were introduced since 0.5.6-r3. We
previously used "global" as Ip6AddrType but in the meanwhile a check was added that
rejected "global" IPv6 addresses that begin with "fc" or "fd". After probing around a bit,
we figured that a type of "unique-local" was the right one to choose in our case.

Now something really weird happened, OLSRd managed it to determine the interface IPv6
address and reported it correctly with -d 5 but then corrupted the address when converting
it from the string to an address struct (e.g.: fdca:ffee:babe:dada:202:6fff:fe4a:31f4/64
suddenly became 202:6fff:fe4a:31f4::/64). Henning helped me to debug that problem and we
came up with a patch that just changed some debug printf()'s but seemed to address this
issue. [6]

After some more tries and recompilations, the OLSRd tip worked nicely together with the
0.5.6-r3 versions and IPv6 addresses on the mesh interfaces.

Finally we wanted to install OLSRd on our x86 BGP router machine (running Debian) but
couldn't get it to work with IPv6. The OLSRd successfully received and transmitted routes
with the mesh network but every attempt to insert kernel routes was answered with an
Invalid Argument error from the kernel. After tinkering around a bit and trying different
OLSRd versions with different modifications the machine died because of a disk failure :(

So we took an old laptop running x86 OpenWrt and installed the OLSRd there. To our
surprise routes were successfully added and everything was well in contrast to Debian.
This leaves us a bit clueless why it works on OpenWrt but not on Debian, this is a thing
we still have to investigate.


All in all it was a nice experience and we were really surprised that we even manged it to
setup a pure IPv6 mesh with OLSRd :D

I personally really appreciate the work you put into OLSRd and hope that this little real
live experience report keeps you motivated to fix and enhance IPv6 support for OLSR ;)

We now plan to build a permanent IPv6 test mesh network so that the OLSR developers have a
real live testbed for IPv6-related issues.


Greetings from the 25c3,
JoW + Freifunk Crew


References:
[1] http://blogs.k-ita.de/~alx/?tag=siit
[2] http://quamquam.org/~jow/6mesh.png
[3] https://events.ccc.de/congress/2008/wiki/Wireless:ipv6-config
[4] http://quamquam.org/~jow/6mesh-screenshots/
[5] + [6]
https://luci.subsignal.org/trac/browser/luci/trunk/contrib/package/olsrd-luci/patches/010-olsrd-ip6addr.patch
https://luci.subsignal.org/trac/browser/luci/trunk/contrib/package/olsrd-luci/patches/011-olsrd-ip6addr-2.patch
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