Mixing fixed-address host declations in dhcpd.conf with dynamic entries created via omapi
Kristian Pedersen
kristian.pedersen at vejen-net.dk
Tue Jul 17 13:33:53 UTC 2012
On 07/17/2012 01:57 PM, Simon Hobson wrote:
> Kristian Pedersen wrote:
>
>> So the question goes, how does the dhcp server handle overlaps in
>> dhcpd.conf vs. dynamic entries in dhcpd.leases?
>
> It doesn't - DON'T DO IT
>
>> When the server starts up and checks the dhcpd.leases, will any
>> config in dhcpd.conf override the ones from the lease-file? Do you
>> see any problems in this implementation or have suggestions for other
>> ways to implement this?
>
> There are no checks, it's assumed that the administrator knows what he
> is doing ! Depending on various factors, it may result in the address
> being marked as abandoned in the leases file (fairly innocuous), or at
> the other extreme it may result in two clients being given the same
> address.
>
> The simple answer is : never have an address i a dynamic range AND a
> fixed address statement. If you must have a fixed address in the
> middle of a dynamic range, then split the range :
>
> range 192.168.1.10 192.168.1.56
> range 192.168.1.58 192.168.1.99
> ...
> fixed-address 192.168.1.57
I think there is a misunderstanding here (most likely bad wording from
my side :). Maybe it is the "dynamic" wording? The host entries added
through omapi on the fly, and then later via dhcpd.conf are all
"fixed-address", and never within a pool/range ip area.
In dhcpd.conf a lease might look like:
host pc0018f8afeded {
hardware ethernet 00:18:f8:af:ed:ed;
fixed-address 10.110.1.27;
}
I found an example of a what a static lease added through OMAPI might
look like in dhcpd.leases (
http://jpmens.net/2011/07/20/dynamically-add-static-leases-to-dhcpd/ ):
host pc0018f8afeded {
dynamic;
hardware ethernet 00:18:f8:af:ed:ed;
fixed-address 10.110.1.27;
}
What (is supposed) to happen if the server has both above fixed-address
assignments?
> As an alternative, you may wish to consider whether reserved leases
> would suit your needs. A reserved lease is just like any other, goes
> through the same lifecycle, takes part (properly) in dynamic DNS
> updates, and is recorded in the leases file. However, being marked as
> reserved, it will not be reused (even if long expired) for any other
> client.
> I believe you should be able to create a lease and mark it reserved,
> or just mark an existing lease as reserved, via OMAPI.
I looked a bit into reserved leases, but I dont think they fit my
scenario very well since i am not really interested in dynamic/pool
assigned addresses.
Regards,
--
Kristian Pedersen
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