Question on DHCP lease expiration

[Patrick Trapp]

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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