Multiple Leases for one client (id)

[Kim Kinnear <[e-mail]>]

In the process of testing our DHCP server, we have come across the
following question, and perhaps some of you that have already been
through this have some suggestions.

The case we are concerned with is the mapping from client id to a
leased IP address.  If a client gets a lease from our server, and then
sometime later asks for (via DISCOVER) another lease by specified IP
address, we come to an interesting implementation decision.  (Note that
both of these interactions use the same client id.)

We could offer him the existing lease that we already show as valid for
him (which we would find by looking it up by client id).
Alternatively, if the lease for which he is asking is available, we can
go ahead and offer it to him.  If we offer him this additional lease,
we then have two outstanding and valid leases for one client id.

Having two outstanding leases doesn't seem to violate the RFC's. Of
course it is unlikely to be a common situation (though we can construct
cases where it could occur with dual-boot systems or laptops with
removable hard drive cartridges).

The fundemental question seems to be:  do we allow a specific client id
to have more than one valid lease outstanding at any one time, or not?

This becomes a bit more of a interesting question when reserved leases
are considered, since our first approach of "sure, why not give him two
leases if he really seems to want them" sort of breaks down.  If the
client doesn't have a reserved lease, having two leases outstanding
makes sense (in a limited sort of way), but if he does, then it is our
belief that he probably shouldn't be allowed to get any address but the
one reserved for him (since the system admin seems to lose what limited
control he or she has otherwise).

Any thoughts on any of this?

Apologies for not searching the archives of this list, but we couldn't
seem to get at them.

Thanks -- Kim