[Babel-users] A Babel experiment at funkfeuer.at

Harald Geyer harald at lefant.net
Mon Dec 15 00:46:11 UTC 2008

> >> Hmm... the current implementation of Babel requires IPv6 in the kernel.
> Let me explain a little more.

> However, the current implementation only works over IPv6: while Babel will
> route IPv4, IPv6 or both, the Babel messages will only be transported over
> IPv6.  (There are very good reasons to prefer IPv6 for transporting
> protocol messages, most notably the fact that it makes it easier to
> implement routing over unnumbered interfaces -- i.e. a router is able to
> forward packets even before it's been assigned an address, or when only
> some interfaces have an address.  Additionally, the IPv6 multicast APIs are
> somewhat more portable than the IPv4 ones.)
> I'd like to be clear that you don't need global IPv6 addresses, you don't
> need router advertisements, you don't need global IPv6 connectivity.  You
> only need kernel support for IPv6, which is all that's needed to do
> link-local multicast.

Yes, that was my assumption. My point is: loading IPv6 support into the
kernel is expensive - configuring some global IPv6 addresses is not.

> > So on an openwrt router you need kmod_ipv6 installed ... we have such
> > a setup (using 6to4 and radvd)
> Once again -- you don't need 6to4, you don't need radvd, you only need the
> IPv6 kernel module.

Sure, it's just the only way I have been able to verify that IPv6
support works in freifunkfirmware ...

> > With olsrd and ipv6 and babel and openvpn or vtun and $monitor_tool
> > running on the same mesh node we will most likely hit the RAM limit.
> FWIW, I'm happily running Babel + ahcpd + ntpd on 16MB OpenWRT machines
> (MIPS).  Ntpd is the largest of the three ;-)

Once I have some proof of concept setup for freifunkfirmware I will
be able to say more about that.

> I don't know about vtun, but I know that Babel happily runs over SIT
> tunnels, IP-IP tunnels, GRE tunnels and OpenVPN.  For IP-IP, GRE and
> OpenVPN, a small hack is needed.  For IP-IP, a recent kernel is needed.
> I have no idea about vtun.

Ok. I was under the wrong assumption, that babel would need some 
ethernet type network interface. If we don't need OpenVPN then this
should save quite some RAM...

> I'm using OpenVPN and GRE in my network.  Since vtun is insecure anyway,
> I don't see any reason to prefer it to GRE.
> > OTOH if we need IPv6 support in the kernel anyway, then I don't see
> > a reason not to do the whole experiment in IPv6 space - but perhaps
> > I miss something.
> Don't worry about that -- it's a hybrid protocol.  You can do both, or
> either, or have some nodes doing IPv6 and other doing IPv4.  By default,
> Babel will route IPv6 on all interfaces, and route IPv4 on all interfaces
> that have an IPv4 address.
> So as long as you get Babel running, you don't need to choose between IPv4
> and IPv6 -- you get whatever protocol you have configured addresses for.

Sure, but since in Vienna olsr manages IPv4 and only IPv4 why not use
babel together with IPv6? That way I don't need to worry about how to
claim some IPv4 subnet for babel and I don't need to configure addresses
on all nodes participating in the experiment: Just install babel + some
special config file and it will route via IPv6 link local addresses by
default. Just install some gobal addresses on nodes used for monitoring.
Is that too simple?


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