[CentOS] dhcpd frequent renewals

Wed Feb 17 14:48:38 UTC 2016
Rob Kampen <rkampen at kampensonline.com>

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,
> 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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