[Babel-users] AHCP thoughts

[Gabriel Kerneis]

Mitar,

On Tue, Jun 15, 2010 at 11:03:08PM +0200, Mitar wrote:
> "Unlike AHCP 0, AHCP 1 requires that servers have read-write persistent
> storage; a small flash should be enough, but you'll not be able to run AHCP
> 1 servers on disk-less, flash-less netbooted nodes."
> 
> Does this mean that they need persistent storage across reboots?

Just like dhcp does, yes.  You might have lease clashes otherwise.

By the way, please not that if you use /var/lib/leases on OpenWrt, this is a
temporary directory which will not be retained across reboots.  Use
/lib/leases, for example.

> "For the same reason, a node will not be able to autoconfigure unless it can
> reach a server."
> 
> This is problematic in mesh splits. [...]
> In such networks splits will be common. You will go around and you
> will lose connectivity, one group will be connected (in a classroom
> for example) but not connected to another group. Somebody reboots its
> mobile phone - how it will configure?

It will use IPv6.

You just cannot cast a random IPv4 without a significant risk for clashes.
You need a central server (or several of them, but they must serve distinct
prefixes in that case), and if it is down, too bad.  But if this server is your
gateway too, then you shall not be too worried about not having an IP, since
you cannot even reach the Internet.  And if you do not need to reach the
Internet, but only local resources, then there is no reason why you couldn't
build an IPv6-only network.

> Probably we can solve this easily in IPv6 - we just have multiple IPv6
> addresses for every device. Assigned one (if this is possible) and
> also self-assigned one from device's MAC address (but not link-local).
> So for local service-discovery content and services it would work.
> Only the device would not be reachable from the Internet. But if it is
> in split this the device would not be in any case. So the idea is to
> run AHCP server on every Internet gateway and this is it? And use
> additional IPv6 addresses always.

This is how I understand it too, at least.

Best regards,
-- 
Gabriel