Steven M. Bellovin wrote:
[ ... ]
> The laptop was given a lease by dhcpd; that lease was recorded in
> dhcpd.leases.  I stopped dhclient on the laptop, truncated the
> dhclient.leases file, and restarted dhclient.  dhcpd on the server
> gave it a different address.  Why?

As far as I can tell, the ISC dhcp software doesn't make an effort to reassign
the same IP to the machine which used to have the lease if that machine asks for
an entirely new lease.  If the client asks to renew a lease as it expires, it
will get the prior IP, though.

> Section 4.3.1 of RFC 2131 seems to imply that the previous address
> should be reused.

Agreed.  You might try using the OpenBSD version of dhcpd; I've heard they are
trying to work on some of these issues that the ISC version doesn't bother with.

> I did not see any relevant options in the dhcpd.conf man page.  I do not
> have any static addresses assigned in my dhcpd.conf file.

Of course, setting up a static address via DHCP is the ideal solution to this
problem...

-- 
-Chuck