Hi George,
if you are really talking about "and is simply a client talking to other clients" as you said before, then IPv6 autoconf is the way to go as Andrew mentioned before.
Are any freifunk networks purely peer-to-peer, without any "server" or "core" nodes ?
That is, are any freifunk networks using ipv6 autoconf, or zeroconf ?
Here in Lübeck we are currently experimenting with such an IPv6-mesh-only network. Because of BTM-Adv a completely adhoc ip-assignment is possible as long as your mac adresses in your network are unique (as they should be). If it were just for communications inside of the mesh without any routing from this mesh to hosts outside of the mesh, you can even use the automatically assigned link-local adresses - this is working out of the box in most current operating systems.
So basically our intention is to not have the mesh network as an uplink directly to the internet but more as a dedicated metropolitan area network, a switched "LAN". In this MAN everyone shall be free to set up VPNs for their internet gateway / to their home network. Of course this is a trade-off about usability on the other hand as setting up a VPN is not a trivial task for "common" people... but don't know what your specific goal is. Could you expain your intention a little further maybe?
We were also running in some trouble with those link-local adresses, not all applications seem to support this properly. Therefore we were assigning additional ipv6 unique local addresses with the help of radvd (and limited this to the local wifi/ethernet clients on one router with the help of ebtables). (this should also be possible with dhcpv6 instead of using radvd though, I guess)
I'm not aware of any routing protocol supporting dynamic, decentral ipv4+6 internet gatewaying over a ipv6-only mesh network yet. Though there are discussions about how this could be achieved on the BATMAN-Adv side as well. I'm also curious about what the Berlin Freifunk guys are up to with NIIT, gotta have a look at the workshop/discussion during the 26c3. Has anyone heard of IVI (or totd) yet? I think this should make routing packets between the ipv4 and ipv6 stack possible.
Cheers, Linus