Question on DHCP lease expiration

[Glenn Satchell]

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 foo.example.org;" 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 gmail.com> 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 isc.org>
>>> To: Users of ISC DHCP <dhcp-users at lists.isc.org>
>>> Subject: Re: Question on DHCP lease expiration
>>> Message-ID: <7321B2AD-8133-448B-A328-22AC85DADEDC at isc.org>
>>> 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 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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