Static IP and IP management

[Bernard Fay]

Thanks Glenn,

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.

Thanks,
Bernard



On Thu, Feb 25, 2016 at 7:10 PM, Glenn Satchell <glenn.satchell at uniq.com.au>
wrote:

> 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 <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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> >>
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