[Babel-users] Question about AHCP

[Henning Rogge]

Am Freitag 27 November 2009 16:31:57 schrieb Juliusz Chroboczek:
> > If I got the README file right every node in a mesh needs to run AHCP in
> > client mode and you can install any number of AHCP-servers.
> 
> Yes.
> 
> (Just to be pedantic: a mesh node can also be configured statically, in
> which case it only needs to run ahcpd in forwarder mode.)
Okay.

(If the network would have a mesh-wide multicast implementation, you could 
just use it and forget about the forwarders, right ?)

> > Every server needs it's own IP range which cannot be shared with other
> > AHCP- servers.
> Yes, for IPv4 stateful configuration.
> 
> For IPv6 stateless configuration, it is okay if all servers announce the
> same prefix.
IPv6 can be a lot less painful.
 
> > Does this mean I have to reconfigure the olsr AHCP-servers to add more
> > AHCP- servers to the net, because they must give away some of their IPs ?
> For IPv4 stateful configuration, yes, that's the case.
> 
> > What happens when one AHCP-server is dropping of the net ? Do every
> > client of it's IP range gets a new address from another servers IP range
> > ?
> Yes, but only after trying really hard to contact the original server.
> 
> Suppose a client C has been configured by server S1.  A few minutes
> before its lease expires, C will try to contact S1 using unicast to
> renew its lease.  If that fails, after a few minutes it will assume that
> something bad has happened to routing, and it will try to contact S1
> using flooding.  If that still fails, it will try to contact any server
> using flooding.
My problem with AHCP for IPv4 is that it's a little bit difficult to manage in 
a mesh with a "distributed" administration. Do you ever planned to add the 
possibility that AHCP-servers could somehow "trade" free IP space so you don't 
need the totally strict IP separation of servers. Or maybe to distribute the 
leases to other AHCP-servers so you have some redundancy ?

Henning Rogge
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