In dhcpd.conf there are some entries that resemble this:

host alvin {
hardware ethernet [deleted]; # hardwired
hardware ethernet [deleted]; # wireless

The intent here is to provide the same IP address to Alvin's laptop
whether he connects using a wireless access point or the hardwired
network. My problem is that when switching from wired to wireless, the
wired IP is still leased out, so instead of being assigned again, Alvin gets something from the dynamic IP pool.
I cannot guarantee that the client machines will explicitly relinquish
their IP leases, especially when the cable is yanked out to go from
wired to wireless.

I want to stop dhcpd from going to the dynamic IP pool and instead
return what's specified by the "fixed address" line no matter if it's
currently still leased out. In other words, expire that lease and
issue a new lease to the new MAC address. How do I do this?

David Griffith <-- Switch the 'b' and 'u'