Re: [B.A.T.M.A.N.] "Distributed" DHCP vs gateway

[The Doctor <drwho@virtadpt.net>]

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On 08/06/2011 10:19 AM, Ryan Hughes wrote:

> 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.

That is fairly easy to do.  A given mesh runs the risk of two colliding
IP addresses, but that is easy enough to evade if one picks a large
enough potential address space.

> 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.

That would indeed work.  One could also write a small utility which
pseudo-randomly chose an IP address from one of the RFC-1918 ranges (for
example) and just configured itself with ifconfig.  This is what I have
been doing:

https://github.com/Sitwon/Byzantium/blob/master/control_panel/networkconfiguration.py#L321

> 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.

<makes a mental note>

I was unaware of this; I had assumed that, once a client had grabbed IP
configuration information, it would simply ignore any other DHCPOFFERs.

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

For what it is worth, it seemed to work fairly well in small-scale
experiments.

> 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 have not seen it do that in operation.

> Is this idea just too crazy?  Why?

It does not sound too crazy, but slightly overcomplicated for what you
seem to want to use it for.

- -- 

The Doctor [412/724/301/703]

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