ISC DHCP server offers fixed IP addresses to ANY device!

David W. Hankins David_Hankins at
Mon Dec 22 18:43:34 UTC 2008

On Sat, Dec 20, 2008 at 02:37:35PM +0530, Jatinder Goswami wrote:
> Can you please let us know how to configure dhcpd for reserved IP
> functionality.

'fixed-address' declarations are distinct from the idea of reserved
dynamic allocations.  Because fixed-address setups do not carry a
lease through the resulting states, there is no hard drive access,
and consequently, no fsync-rate limit to response performance.

But this doesn't really answer your question either.

When I added reserved IP support, it was new, and I wasn't really sure
how it would be used (most people seem to prefer fixed-address
statements for aforementioned simplicity reasons, 'reserved' flagged
leases seemed at the time to be largely only useful to MS->ISC
conversions, and as such, probably done once at lease-database-
migration time).  So the only ways to reserve an IP address out of
a dynamic pool right now are to edit dhcpd.leases inbetween a restart,
to use OMAPI, or to try the "infinite-is-reserved" feature, which was
a kind of shot in the dark on my part in the area of not-migrating
reserved lease support.

None of those are really good options.  In retrospect, now that I've
seen how folks plan to use it, I think we could have supported a
situation where the server is directed to reserve leases for specific
host records (just add a 'reserve' boolean config value) or classes,
and this could at least be used for hosts that do not roam around the

This would probably take betwen 5-10 lines of code, if anyone feels
like contributing it.

In other news, we're looking at better database backends (and a mode
of operation that is not memory based), and better CLI tools for
runtime configuration management.

Ash bugud-gul durbatuluk agh burzum-ishi krimpatul.
Why settle for the lesser evil?
David W. Hankins	"If you don't do it right the first time,
Software Engineer		     you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins
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