[Dnsmasq-discuss] DHCP leases in multiple VLANs

Ferenc Wagner wferi at niif.hu
Wed Sep 15 19:49:47 BST 2010

Simon Kelley <simon at thekelleys.org.uk> writes:

> Ferenc Wagner wrote:
>>> DHCP clients should maybe do this anyway: it's dodgy to have the same
>>> MAC address in more than one broadcast domain at the same time.
>> Could you please explain why that is dodgy?
> If there can be only a single lease for a unique MAC address then  a
> single host can't create lots of leases and use up all the available
> adresses. Relaxing this to allow only one lease per subnet requires that
> the DHCP server have an accurate view of whether two addresses are in
> the same subnet.

Then what about relaxing it to allow only one lease per dhcp-range?

>>> It may be possible to relax dnsmasq a bit: really only the IP address
>>> needs to be unique in the lease database, but I'm not quite sure there
>>> wouldn't be obscure consequences.
>> Maybe if several subnets are used in one VLAN...  But as far as I can
>> see, ISC DHCPD does something like this (the lease file is keyed by IP
>> address only) and it seems to fare quite well.  Please consider enabling
>> this in dnsmasq, too (although its lack isn't a show-stopper for me
>> right now).
> I think it's possible, but it's one of those changes that makes me
> nervous: it feels like there's the possibility of breaking lots of
> current installations.

Maybe make it disabled by default, and add a config option to enable it?

More information about the Dnsmasq-discuss mailing list