Leases based on MAC addresses

sthaug at sthaug at
Sun Feb 8 21:10:53 UTC 2009

> If a client always gets the same IP based on MAC address... that is
> a static lease. You must reserve the IP address for that system or
> you risk duplicates... so it can no longer be part of a dynamic
> pool. What you are looking for is a registration system that builds
> a configuration file. Minimally it sounds like you want something to
> scan your leases and update your configuration as dynamic addresses
> transition to static.

For me this is situation is not quite the same as a static lease. Aside
from possibly breaking the standard, I think it's perfectly reasonable
to want a DHCP server with the following characteristics:

- Leases should *always* be based on MAC address, not UID. If the same
MAC address asks again, it should always receive the same answer. One
implication of this is only one IP address per MAC address. Another is
that as soon as a MAC address has been "seen" by the DHCP server, the
IP address handed out by the server must be remembered "forever" (or
at least until manually removed).
- The actual value of the IP address itself is uninteresting (server
can pick) - this makes it different from a static lease.

Steinar Haug, Nethelp consulting, sthaug at

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