randomly(!) assign ip's from dynamic address range

[Simon Hobson]

Roberto Innocente <inno at sissa.it> wrote:

> Don't forget also rfc 4436 (Detect network attachment)
> used in particular by iphones and ipads that are so nice to switch
> almost instantaneously from a wifi ap to another (less than 1 second).
> This is done (when the lease is still valid) without re-negotiating
> anything with the dhcp server and , provided they recognize the mac address
> of the default router, continue to use the old lease address.

That won't matter (much). The OP has stated that they can't detect users leaving the network anyway, so the only way to determine a client is "down" is to see it's lease expire. Thus the address will only be "locked" when the lease is expired and the client should not be trying to use it. As long as the client returns to the network (even briefly) during the period the address is locked then it'll negotiate a new address with the DHCP server.

The only problem I see is a multihomed device which is "away" for so long that the locking lease expires and so allows the client to get it's old address back.


One thing I didn't see was anything about how clients connect : is this a "all devices go on the network directly" type of thing, or do users have a router on their end and their end devices behind that (and a layer of NAT) ? If the latter then it really doesn't matter what end user devices are used - it's the router that gets the public address.