update static leases
Simon Hobson
dhcp1 at thehobsons.co.uk
Wed Aug 22 07:14:07 UTC 2007
Richard Smits wrote:
>Can anyone please give me some information about this ? I am confused.
>The following scenario :
>----
>ISC DHCP server with the folowing (relevant) options :
>----
>ddns-hostname= host-decl-name;
>ddns-update-style interim;
>ddns-updates on;
>zone domain.net. {primary 1.1.2.2; key DHCP_UPDATER;}
>use-host-decl-names on;
>update-static-leases on;
>
>subnet 11.18.16.0 netmask 255.255.248.0 {
> option domain-name "domain.net";
>
>Folowing are the host statements......
>
>DDNS updates are working fine, but the records of old pc's are NOT
>removed. If I read the manual right, the "update-static-leases on" flag
>is the reason for this, because :
>It is not recommended because the DHCP server has no way
>to tell that the update has been done, and therefore will not delete the
>record when it is not in use.
>
>Now the big question : If I CHANGE an IP number or a Hostname , will the
>record be updated ???
Possibly. If the hostname is the same then the records should get
replaced, but if the hostname is changed then NEW records will be
created.
>The record excists, so the server would be able to change it, right ?
Wrong. The way fixed host declarations work is to bypass much of the
normal processing - including recording the lease in the leases file.
It is through the leases file that the server records what DNS
records it has created, just deleting (or modifying) a host
declaration with fixed address merely removes all knowledge of it (or
it's previous state) from the servers history.
You would probably be better off with reserved leases which is a new
feature in 3.1.0. Here you set a lease to reserved (currently
requires editing the leases file or using omapi) and then the lease
is reserved for that client rather than getting recycled eventually
for another client. But beyond this it has two important differences:
the lease goes through the normal state processing (so dns creation &
removal) and I believe all the class processing is done (so class
specific options should work properly).
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