failover - reserved address

Pavel Mlčoch pavkamlc at
Thu May 21 08:22:30 UTC 2009

Sorry for this question, but I don't found any solution for reserved leases in my case. When I use reserved leases, I cannot say which configuration may server sent to client. I'd like create leases file by hand (script), but I must say what subnet or router may be used, because in static IP addresses we have denied client with unknown MAC address and this we have to in leases too. I think the best way is declare two subnets, one with right router for known clients and second with wrong router and another subnet for unknown. Is this setting possible? In man page I don’t found how to configure group and subgroup in leases file (


> -----Original Message-----
> From: dhcp-users-bounces at [mailto:dhcp-users-
> bounces at] On Behalf Of Simon Hobson
> Sent: Monday, May 18, 2009 4:14 PM
> To: Users of ISC DHCP
> Subject: RE: failover - reserved address
> Pavel Mlãoch wrote:
> >I don't know if I understand right. When I mark
> >leases by adding line "reserved;" is the same as
> >fixed-address?
> No, they are VERY different features/functions.
> A host statement with fixed address is very
> different to a normal dynamic lease. Although
> from the client side it looks the same, at the
> server end there is no lease processing, no
> dynamic DNS updates, etc - in fact a lease will
> never appear in the leases file for these
> clients. Failover is not involved at all, and you
> should just define the same host statement on
> each server.
> A lease marked as reserved acts EXACTLY like a
> dynamic lease - it appears in the leases file, it
> expires, dynamic DNS updates happens, etc. The
> only difference is that once you add the reserved
> flag, the server will NOT reallocate that address
> to another client, even when it's expired. In a
> failover environment, I assume it goes through
> the same processing as any other lease.
> >Isn't possible use omshell for this change on running server?
> IIRC from previous discussion on here, no you can't.
> --
> Simon Hobson
> Visit for books by acclaimed
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