Hi Bernard,
ISC dhcpd ships with a very comprehensive set of man pages, so I would
suggest perusing these:
dhcpd.conf, dhcpd, dhcp-options, dhcp-eval
In this case the reserved leases are mentioned in the dhcpd.conf man page.
I've included the section below in the hope that google will find it for
future searches.
I would also suggest that you can approximate a reserved lease by setting
the lease time to be very long, say 1 year (31536000 seconds).
regards,
-glenn
man dhcpd.conf
...
RESERVED LEASES
It's often useful to allocate a single address to a single
client, in approximate perpetuity. Host statements with
fixed-address clauses exist to a certain extent to serve
this purpose, but because host statements are intended to
approximate 'static configuration', they suffer from not
being referenced in a littany of other Server Services, such
as dynamic DNS, failover, 'on events' and so forth.
If a standard dynamic lease, as from any range statement, is
marked 'reserved', then the server will only allocate this
lease to the client it is identified by (be that by client
identifier or hardware address).
In practice, this means that the lease follows the normal
state engine, enters ACTIVE state when the client is bound
to it, expires, or is released, and any events or services
that would normally be supplied during these events are pro-
cessed normally, as with any other dynamic lease. The only
difference is that failover servers treat reserved leases as
special when they enter the FREE or BACKUP states - each
server applies the lease into the state it may allocate from
- and the leases are not placed on the queue for allocation
to other clients. Instead they may only be 'found' by
client identity. The result is that the lease is only
offered to the returning client.
Care should probably be taken to ensure that the client only
has one lease within a given subnet that it is identified
by.
Leases may be set 'reserved' either through OMAPI, or
through the 'infinite-is-reserved' configuration option (if
this is applicable to your environment and mixture of
clients).
It should also be noted that leases marked 'reserved' are
effectively treated the same as leases marked 'bootp'.
On Fri, February 26, 2016 2:26 am, Bernard Fay wrote:
> I have to find out about this "reserved" thing. I don't understand it.
> Google, please, help me!
>
>
> On Wed, Feb 24, 2016 at 1:44 PM, Chuck Anderson <
[hidden email]> wrote:
>
>> On Wed, Feb 24, 2016 at 01:17:13PM -0500, Bernard Fay wrote:
>> > When the dhcpd server assign a static IP to a device, it also instruct
>> bind
>> > to add an entry in the DNS zone file. One thing I realized is that if
>> a
>> > device didn't renew his lease, the entry in the DNS zone file is not
>> > removed. I would have thought to use the zone files to know if a
>> device
>> is
>> > in use or not. I had in mind that the lease time would have help to
>> know
>> > if a device therefore an IP is use or not. In other words, a device
>> > requires an IP and the dhcpd server assigned it a statically defined
>> IP
>> > address. The dhcpd server also instruct bind to add an entry in the
>> > appropriate zone file. Eventually the device is turned off, the lease
>> time
>> > reach its limit then I would have expected the dhcpd server to
>> instruct
>> > bind to remove the entry regarding this device but it is not the case.
>> > Then I could have take a look at the zone files to know what is in
>> used
>> and
>> > I would know what is not in use.
>> >
>> > Either I made something in my configuration or I was expecting too
>> much
>> > from dhcpd and bind.
>>
>> You can do that, but you have to use "reserved" leases rather than
>> fixed-address statements. ISC dhcpd doesn't track the expiry of
>> fixed-address leases.
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