Question on DHCP lease expiration

Shawn Routhier sar at isc.org
Sat Feb 27 01:46:04 UTC 2016


The server treats dynamic and static leases differently.

Dynamic leases have a lease structure that moves between
different queues and this is how the server knows when to
expire the lease and thence when to remove it from the DNS.

Static leases don’t have a lease structure and so don’t get
expired and don’t get removed from the DNS.

regards,
Shawn

> On Feb 26, 2016, at 5:37 PM, David Li <dlipubkey at gmail.com> wrote:
> 
> Hi,
> 
> This is my first post here.
> 
> I am testing to see if an expired DHCP lease can result in the removal
> of the corresponding DNS record on Centos 7.
> 
> So far I am able to let DHCP server assign an static IP based on the
> host's MAC address and add a DNS A record. The host is also able to
> refresh its lease every time it expires.
> 
> But when I shut down the host, I don't see the record removed after
> the lease expired (5 min). Even more the syslog doesn't show any
> messages from DHCP server attempting to remove the IP address and
> update the BIND 9 (named) server. So I am thinking there might be
> something wrong or missing in my dhcpd.conf.
> 
> Here is a snippet of my dhcpd.conf:
> 
> 
> # DNS options
> 
> ddns-updates on;
> ddns-update-style interim;
> update-static-leases on;
> authoritative;
> 
> allow unknown-clients;
> use-host-decl-names on;
> default-lease-time 300; #5 min
> max-lease-time 300; #5min
> log-facility local7;
> 
> 
> 
> # static assignment
> #
> host node1 {
>   hardware ethernet 08:00:27:0A:C3:1C;
>   fixed-address 10.4.1.11;
>   ddns-hostname "node1";
> }
> 
> 
> Can anyone help to see what's missing from my configuration?
> 
> Thanks.
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