Static IP and IP management
bernard.fay at gmail.com
Mon Feb 29 20:24:50 UTC 2016
Of course I saw it in the man page but yet I have no clue how to use it and
more specifically how it will be useful for us. I think I'll have to
experiment with it. So far, what I understand is that an IP will be
assigned by dhcpd daemon and the only, and probably good way, to find the
IP assigned to a server will be by doing a nslookup on the hostname. Of
course if proper integration is done with BIND.
On Thu, Feb 25, 2016 at 7:10 PM, Glenn Satchell <glenn.satchell at uniq.com.au>
> 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).
> 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
> 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
> 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 <cra at wpi.edu> 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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