Question on DHCP lease expiration

David Li dlipubkey at
Mon Feb 29 21:07:20 UTC 2016

Hi Glenn,

This is exactly what I am looking for - to be able to *dynamically*
assign IP based on MAC address and automatically remove it from DNS
when the host is gone. I have tested this solution and work well with



On Mon, Feb 29, 2016 at 4:00 AM,  <dhcp-users-request at> wrote:
> Date: Mon, 29 Feb 2016 00:14:09 +1100
> From: "Glenn Satchell" <glenn.satchell at>
> To: "Users of ISC DHCP" <dhcp-users at>
> Subject: Re: Question on DHCP lease expiration
> Message-ID:
>         <e87722033ac8221a1dff6a254ef3bb8a.squirrel at>
> Content-Type: text/plain;charset=iso-8859-1
> Sounds like you just need normal dynamic leases. these will expire when
> the client doesn't renew any more. You can add a host clause to set the
> hostname, "option hostname;" or similar that will carry
> through to the dns system. Just leave out the fixed-address statement.
> Even though it is a 'random' address, if you only use the DNS name to
> access the system then it doesn't matter what the IP address is.
> regards,
> -glenn
> On Sun, February 28, 2016 6:47 am, Patrick Trapp wrote:
>> There was a similar thread to this on this list over the last few days. I
>> believe reserved addresses were suggested rather than static, but you will
>> probably benefit from looking at the archive from the last week to see if
>> that OP was truly looking at the same situation as you.
>>> On Feb 27, 2016, at 11:42 AM, David Li <dlipubkey at> wrote:
>>> I see!
>>> Do you have any suggestions to get around this? I do need to remove
>>> the assignment from the DNS
>>> if the host failed so others won't bother to contact the failed host.
>>> Of course I can let the application to deal with the
>>> timeout but still prefer to resolving this at DHCP/DNS level. It just
>>> seems logical and convenient.
>>> Maybe another related question is if I have to use static lease to map
>>> host MAC to a name to assign the IP. I need to assign meaningful names
>>> to our hosts in order for others to use them. That means the name
>>> assignment has to be based on what kind of application this host runs.
>>> I haven't found other dynamic ways to do this yet. Any suggestions?
>>> David
>>>> Date: Fri, 26 Feb 2016 17:46:04 -0800
>>>> From: Shawn Routhier <sar at>
>>>> To: Users of ISC DHCP <dhcp-users at>
>>>> Subject: Re: Question on DHCP lease expiration
>>>> Message-ID: <7321B2AD-8133-448B-A328-22AC85DADEDC at>
>>>> Content-Type: text/plain; charset=utf-8
>>>> 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> 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;
>>>>>  ddns-hostname "node1";
>>>>> }

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