So, I had a crazy idea the other day:

Normally, when I talk to people about mesh networks, they assume that there is some central authority assigning IP addresses to nodes intelligently.

I was thinking, though, that I'd rather have it so that every node could have the same firmware, and you'd just throw the node up and it'd negotiate everything for itself, including its IP address.

So I was thinking: What if each node in the network was using batman-adv, and ran a DHCP client and a DHCP server? It'd try to get an address thru DHCP. If it failed, it'd choose an address at random from the network range. Then, any time someone threw up a new node in range, the new node would try to get an address, and it would succeed in getting an address from the first node.

Multiple DHCP servers can serve the same, overlapping IP ranges. However, this depends on the DHCPOFFER and DHCPREQUEST being broadcast to the network. This is how we avoid having the same IP address assigned to multiple nodes -- DHCP servers overhear what was assigned to whom by other DHCP servers, and make a note to themselves not to assign that address themselves.

So it seems that a "distributed" DHCP system could work.

The problem is, doesn't Batman-adv munge the DHCP that flows though it, for its gateway logic? So that the DHCPREQUESTs are unicast? That's great for gateway logic. But I also want nodes to have IP addresses for internal communication.

I was thinking of running it like this: Each node has two virtual interfaces - the mesh interface, running in adhoc mode. Routers use this interface, and this is where the distributed DHCP runs.

Another wifi interface runs in host mode. This is what laptops and so forth will connect to.

Once a router gets an ip address from this distributed DHCP nonsense, then it determines a longer network prefix for its clients on the host-mode interface. It sets up its HNAs and starts serving DHCP with this longer prefix to its clients. The machines on the inside run webservers and so forth that should be available to the inside of the mesh.

Now, what if the network is fractured and the same IP address gets assigned to a router (and thus is used as a prefix for that router's clients) on each side of the split? When the segments join up, we'll have multiple nodes with the same IP address and this will cause problems.

Yes. The lease times will be very short, so this type of problem should resolve itself quickly.

But, what do I do about how the gateway business interferes with DHCP? Could I somehow have two DHCP servers serving the same interface? One that serves out IP addresses and one that deals only with gateways?

Is this idea just too crazy? Why?

--Ryan

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Content preview: So, I had a crazy idea the other day: Normally, when I talk to people about mesh networks, they assume that there is some central authority assigning IP addresses to nodes intelligently. I was thinking, though, that I'd rather have it so that every node could have the same firmware, and you'd just throw the node up and it'd negotiate everything for itself, including its IP address. [...]

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