[CentOS] dhcpd frequent renewals

Fri Feb 19 03:46:33 UTC 2016
Rob Kampen <rkampen at kampensonline.com>

On 18/02/16 13:41, david wrote:
> Rob
> DNS service for my clients is provided by my gateway server, the same 
> machine as the DHCPD server.  I think that's what the "option 
> domain-name-servers" line does.  This allows me to provide 192.168 
> addresses to them when they try to access anything inside the house 
> with a name.  If it's not a locally defined name, BIND forwards the 
> request to the internet.
> I'm not sure I understand about dhcpd log and dns log.  I scan 
> /var/log/messages, using the service name as the key.  Looking at 
> 'named' entries, all I see are messages of the form "clients-per-query 
> increased to XX".
I have had entries like:
  --------------------- dhcpd Begin ------------------------

  Unknown Entries:
     Abandoning IP address pinged before offer: 1 Time(s)

As I am not normally anywhere near this server, it is one I remote 
manage, I have not followed up,
I am now implementing a new network for them and hoping all this hassle 
will be a thing of the past.
Sorry I have no other insight.

> I'm still mystified by the fact that only the i-devices (iphone, ipad) 
> exhibit this behavior of rapid dhcpd renewals.  Mac's and PC's don't.
> David
> At 06:48 AM 2/17/2016, you wrote:
>> On 16/02/16 16:59, david wrote:
>>> Folks
>>> This might be the wrong place to ask, but I don't know where to turn.
>>> My internal home network, including wireless, is controlled by a 
>>> Centos6 server, which provides dhcpd services, along with NAT.  I 
>>> have DHCPD configured with the addresses through 
>>> as the range for dynamic allocations.  The 
>>> default-lease time is 1800 seconds, the maximum is 3600 seconds.
>>> My windows clients, and even an ipad-mini behave nicely, asking for 
>>> DHCP renewals once ever five minutes, or at about 80% of the default 
>>> lease time, a behavior I can understand. However, several of my 
>>> guests, with their own iPads, I-watches, iPhones, connect to my 
>>> network (via a wireless access point which does not do routing 
>>> functions) and they're renewing once every 20-30 seconds.  In 
>>> addition, these devices also loose connectivity for brief intervals, 
>>> which seems to be roughly synchronized with dhcp renewal.  This last 
>>> fact I deduce by doing "tail -f /etc/log/messages" and hearing them 
>>> say "lost connection" at just about the same moment the DHCPREQUEST 
>>> and DHCPACK statements show up.
>>> It's difficult to believe that Apple IOS devices (all of which are 
>>> running apple's latest) have a dhcp client problem not shared by 
>>> windows or even linux hosts.
>>> Does anyone have any clues?
>> does your dhcpd update the dns? name resolution for devices seems to 
>> be required for some applications and thus the dns needs to know 
>> about the leases. Have you checked your dhcpd log entries and your 
>> dns log entries? I have had situations where the dhcpd lease is 
>> dropped due to not being able to complete dns update of the info - 
>> thus the client retries again and again - they do get onto the 
>> internet but the connection drops and a new lease is requested,
>> HTH
>>> David Kurn
>>> San Francisco
>>> DHCPD.CONF file is excerpted below:
>>> ----------------------------------------
>>> ddns-update-style            none;
>>> subnet netmask {
>>>     authoritative;
>>>     option routers   ;
>>>     option subnet-mask;
>>>     option broadcast-address;
>>>     option domain-name        "daku.org";
>>>     option domain-name-servers;
>>>     option netbios-name-servers;
>>>     option time-offset        -28800;    # Pacific standard time
>>>     range dynamic-bootp;
>>>     default-lease-time        1800;
>>>     max-lease-time            3600;
>>> }
>>> --------------------------------------------
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