dhclient renewing ip address lesser then 50% of configured lease period

Glenn Satchell glenn.satchell at uniq.com.au
Wed Nov 25 15:07:27 UTC 2015 

The client is free to request a renewal whenever it likes. The
default-lease-time is only applied when a client does not specify a lease.
So your client is behaving within the standards.

The max-lease-time caps the maximum lease time even if a client asks for a
longer time. There is also min-lease-time to set a minimum. However, the
client can still ask for a renewal at any time.

regards,
-glenn

On Thu, November 26, 2015 1:06 am, Bob Harold wrote:
> On Tue, Nov 24, 2015 at 11:42 PM, srinirao <iamspl_xxx at yahoo.com> wrote:
>
>>
>> Hello, I have my embedded device running dhclient 3.2.18 release. I have
>> configured the dhcp server lease time as:
>>
>> max-lease-time    28800;
>> default-lease-time 7200;
>>
>> Inspite of configuring default lease time to 2 hours, i get frequent
>> dhcp
>> request going out of my device. The requests go out at a freqnency of 50
>> minutes every time. I have read in the online documents that DHCP renew
>> request (unicast) can happen after the completion of 50% of lease time
>> configured. But however I find it hard to understand why this (magic
>> number) 50 minutes here.
>>
>> I am getting very frequent DHCP updates of approximately 50 minutes in
>> /var/log/messages
>>
>> Nov 10 10:34:05 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 10 10:34:05 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 10 10:34:06 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 3240 seconds.
>> Nov 10 11:28:06 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 10 11:28:06 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 10 11:28:06 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 3364 seconds.
>> Nov 10 12:24:11 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 10 12:24:11 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 10 12:24:11 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 3117 seconds.
>> Nov 10 13:16:08 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 10 13:16:08 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 10 13:16:09 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 3127 seconds.
>> Nov 10 14:08:16 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 10 14:08:16 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 10 14:08:16 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 3578 seconds.
>> Nov 10 15:07:54 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 10 15:07:54 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 10 15:07:55 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 2843 seconds.
>> Nov 10 15:55:19 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 10 15:55:19 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 10 15:55:19 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 3206 seconds.
>> Nov 10 16:48:45 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 10 16:48:45 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 10 16:48:45 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 3001 seconds.
>> Nov 10 17:38:46 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 10 17:38:46 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 10 17:38:46 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 3227 seconds.
>> Nov 10 18:32:33 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 10 18:32:33 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 10 18:32:33 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 3247 seconds.
>> Nov 10 19:26:41 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 10 19:26:41 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 10 19:26:41 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 3512 seconds.
>> Nov 10 20:25:13 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 10 20:25:13 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 10 20:25:14 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 2853 seconds.
>> Nov 10 21:12:47 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 10 21:12:47 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 10 21:12:47 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 3146 seconds.
>> Nov 10 22:05:13 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 10 22:05:13 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 10 22:05:13 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 2776 seconds.
>> Nov 10 22:51:29 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 10 22:51:29 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 10 22:51:30 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 3359 seconds.
>> Nov 10 23:47:29 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 10 23:47:29 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 10 23:47:29 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 3039 seconds.
>> Nov 11 00:38:08 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 11 00:38:08 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 11 00:38:08 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 2998 seconds.
>> Nov 11 01:28:07 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 11 01:28:07 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 11 01:28:07 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 3200 seconds.
>> Nov 11 02:21:28 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 11 02:21:28 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 11 02:21:28 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 2866 seconds.
>> Nov 11 03:09:15 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 11 03:09:15 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 11 03:09:15 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 3378 seconds.
>> Nov 11 04:05:33 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 11 04:05:33 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 11 04:05:33 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 3580 seconds.
>> Nov 11 05:05:13 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 11 05:05:14 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 11 05:05:14 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 3539 seconds.
>> Nov 11 06:04:13 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 11 06:04:13 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 11 06:04:13 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 2772 seconds.
>> Nov 11 06:50:25 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 11 06:50:25 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 11 06:50:26 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 3126 seconds.
>> Nov 11 07:42:32 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 11 07:42:32 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 11 07:42:32 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 3087 seconds.
>> Nov 11 08:33:59 XXX-XXXX dhclient4: DHCPREQUEST on eth0 to 10.14.176.70
>> port 67
>> Nov 11 08:33:59 XXX-XXXX dhclient4: DHCPACK from 10.14.176.70
>> Nov 11 08:33:59 XXX-XXXX dhclient4: bound to 10.14.180.135 -- renewal in
>> 2779 seconds.
>>
>> and so on.
>> My DHCP client configuration file only has following options enabled:
>>
>> request subnet-mask, broadcast-address, time-offset, routers,
>> domain-name, domain-name-servers, host-name,
>> netbios-name-servers, netbios-scope;
>>
>> And my lease file logs these responses (approximately every 50 minutes)
>> as
>> :
>> lease {
>>   interface "eth0";
>>   fixed-address 10.14.180.135;
>>   option subnet-mask 255.255.255.128;
>>   option routers 10.14.180.129;
>>   option dhcp-lease-time 7200;
>>   option dhcp-message-type 5;
>>   option domain-name-servers 10.14.176.70,10.14.176.2;
>>   option dhcp-server-identifier 10.14.176.70;
>>   option domain-name "b08.okc.mydomain.com.";
>>   renew 3 2015/11/18 05:37:22;
>>   rebind 3 2015/11/18 06:26:23;
>>   expire 3 2015/11/18 06:41:23;
>> }
>> lease {
>>   interface "eth0";
>>   fixed-address 10.14.180.135;
>>   option subnet-mask 255.255.255.128;
>>   option routers 10.14.180.129;
>>   option dhcp-lease-time 7200;
>>   option dhcp-message-type 5;
>>   option domain-name-servers 10.14.176.70,10.14.176.2;
>>   option dhcp-server-identifier 10.14.176.70;
>>   option domain-name "b08.okc.mydomain.com.";
>>   renew 3 2015/11/18 06:28:43;
>>   rebind 3 2015/11/18 07:22:22;
>>   expire 3 2015/11/18 07:37:22;
>> }
>> lease {
>>   interface "eth0";
>>   fixed-address 10.14.180.135;
>>   option subnet-mask 255.255.255.128;
>>   option routers 10.14.180.129;
>>   option dhcp-lease-time 7200;
>>   option dhcp-message-type 5;
>>   option domain-name-servers 10.14.176.70,10.14.176.2;
>>   option dhcp-server-identifier 10.14.176.70;
>>   option domain-name "b08.okc.mydomain.com.";
>>   renew 3 2015/11/18 07:14:31;
>>   rebind 3 2015/11/18 08:13:43;
>>   expire 3 2015/11/18 08:28:43;
>> }
>> lease {
>>   interface "eth0";
>>   fixed-address 10.14.180.135;
>>   option subnet-mask 255.255.255.128;
>>   option routers 10.14.180.129;
>>   option dhcp-lease-time 7200;
>>   option dhcp-message-type 5;
>>   option domain-name-servers 10.14.176.70,10.14.176.2;
>>   option dhcp-server-identifier 10.14.176.70;
>>   option domain-name "b08.okc.mydomain.com.";
>>   renew 3 2015/11/18 08:01:46;
>>   rebind 3 2015/11/18 08:59:31;
>>   expire 3 2015/11/18 09:14:31;
>> }
>> lease {
>>   interface "eth0";
>>   fixed-address 10.14.180.135;
>>   option subnet-mask 255.255.255.128;
>>   option routers 10.14.180.129;
>>   option dhcp-lease-time 7200;
>>   option dhcp-message-type 5;
>>   option domain-name-servers 10.14.176.70,10.14.176.2;
>>   option dhcp-server-identifier 10.14.176.70;
>>   option domain-name "b08.okc.mydomain.com.";
>>   renew 3 2015/11/18 08:57:34;
>>   rebind 3 2015/11/18 09:46:46;
>>   expire 3 2015/11/18 10:01:46;
>> }
>> lease {
>>   interface "eth0";
>>   fixed-address 10.14.180.135;
>>   option subnet-mask 255.255.255.128;
>>   option routers 10.14.180.129;
>>   option dhcp-lease-time 7200;
>>   option dhcp-message-type 5;
>>   option domain-name-servers 10.14.176.70,10.14.176.2;
>>   option dhcp-server-identifier 10.14.176.70;
>>   option domain-name "b08.okc.mydomain.com.";
>>   renew 3 2015/11/18 09:51:31;
>>   rebind 3 2015/11/18 10:42:34;
>>   expire 3 2015/11/18 10:57:34;
>> }
>> and so on.
>>
>> What could I be doing wrong? According to me, the ip address should not
>> need to change that often.
>>
>> Please help
>> srini rao
>>
>> After a outage, or when everyone arrives at the office at the same time,
> many clients will get leases at the same time.  To avoid the renewals all
> happening at the same time, the DHCP varies the renewal time a little.
> Notice the "renewal in 3539 seconds." in your log.  I see it varying from
> 46 to 60 minutes in your log.  This is exactly what you should expect.  If
> you want less frequent renewals, you could change to 8 hour leases.  I
> use:
>
> min-lease-time 28800;
> default-lease-time 28800;
> max-lease-time 28800;
>
> --
> Bob Harold
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> dhcp-users at lists.isc.org
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