[CentOS] dhcpd frequent renewals

Thu Feb 18 18:41:34 UTC 2016
david <david at daku.org>

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'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.


At 06:48 AM 2/17/2016, you wrote:
>On 16/02/16 16:59, david wrote:
>>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,
>>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;