Logging DHCP lease duration in seconds

Discussion:

Alp Eren Kose

2015-10-02 18:31:33 UTC

Hi,

I have an easy question I believe, I want to log DHCP lease durations given
to clients, I tried the following, however it appears most of the time,
logs are showing half of the lease duration.

log(info, concat( "IP: ", binary-to-ascii(10, 8, ".", leased-address), " ;
", "leasetime:", binary-to-ascii(10,32,"",encode-int(lease-time,32)) ));

I have set the following lease time values for a pool:

subnet 172.16.2.0 netmask 255.255.255.0 {
option routers 172.16.2.1;
pool {
failover peer "failover-partner";
default-lease-time 300;
min-lease-time 300;
max-lease-time 300;
range 172.16.2.10 172.16.2.250;
}
}

And this configuration produces an output like this:

Oct 2 14:34:44 mercan dhcpd: IP: 172.16.2.127 ; leasetime:155
Oct 2 14:37:10 mercan dhcpd: IP: 172.16.2.127 ; leasetime:154
Oct 2 14:37:13 mercan dhcpd: IP: 172.16.2.127 ; leasetime:297
Oct 2 14:39:37 mercan dhcpd: IP: 172.16.2.127 ; leasetime:156
Oct 2 14:42:03 mercan dhcpd: IP: 172.16.2.127 ; leasetime:154
Oct 2 14:44:28 mercan dhcpd: IP: 172.16.2.127 ; leasetime:155
Oct 2 14:46:53 mercan dhcpd: IP: 172.16.2.127 ; leasetime:155
Oct 2 14:49:18 mercan dhcpd: IP: 172.16.2.127 ; leasetime:155
Oct 2 14:49:54 mercan dhcpd: IP: 172.16.2.127 ; leasetime:264
Oct 2 14:50:47 mercan dhcpd: IP: 172.16.2.127 ; leasetime:247
Oct 2 14:51:18 mercan dhcpd: IP: 172.16.2.127 ; leasetime:269

How can log the precise lease durations, would be great if anyone has any
suggestions?

Thanks in advance.
Alp

Denis Laventure

2015-10-02 19:51:37 UTC

Permalink

The client will renew the lease at half the max-lease-time. So seeing 150 sec for a 300 sec lease seems normal.

Hi,

I have an easy question I believe, I want to log DHCP lease durations given to clients, I tried the following, however it appears most of the time, logs are showing half of the lease duration.

log(info, concat( "IP: ", binary-to-ascii(10, 8, ".", leased-address), " ; ", "leasetime:", binary-to-ascii(10,32,"",encode-int(lease-time,32)) ));

I have set the following lease time values for a pool:

subnet 172.16.2.0 netmask 255.255.255.0 {
option routers 172.16.2.1;
pool {
failover peer "failover-partner";
default-lease-time 300;
min-lease-time 300;
max-lease-time 300;
range 172.16.2.10 172.16.2.250;
}
}

And this configuration produces an output like this:

Oct 2 14:34:44 mercan dhcpd: IP: 172.16.2.127 ; leasetime:155
Oct 2 14:37:10 mercan dhcpd: IP: 172.16.2.127 ; leasetime:154
Oct 2 14:37:13 mercan dhcpd: IP: 172.16.2.127 ; leasetime:297
Oct 2 14:39:37 mercan dhcpd: IP: 172.16.2.127 ; leasetime:156
Oct 2 14:42:03 mercan dhcpd: IP: 172.16.2.127 ; leasetime:154
Oct 2 14:44:28 mercan dhcpd: IP: 172.16.2.127 ; leasetime:155
Oct 2 14:46:53 mercan dhcpd: IP: 172.16.2.127 ; leasetime:155
Oct 2 14:49:18 mercan dhcpd: IP: 172.16.2.127 ; leasetime:155
Oct 2 14:49:54 mercan dhcpd: IP: 172.16.2.127 ; leasetime:264
Oct 2 14:50:47 mercan dhcpd: IP: 172.16.2.127 ; leasetime:247
Oct 2 14:51:18 mercan dhcpd: IP: 172.16.2.127 ; leasetime:269

How can log the precise lease durations, would be great if anyone has any suggestions?

Thanks in advance.
Alp

Glenn Satchell

2015-10-04 12:47:00 UTC

Permalink

Hi Alp

lease-time shows the remaining time in the lease, not the total time.

This is from the dhcp-eval man page:

lease-time

The duration of the current lease - that is, the differ-
ence between the current time and the time that the lease
expires.

regards,
-glenn

Post by Denis Laventure
The client will renew the lease at half the max-lease-time. So seeing 150
sec for a 300 sec lease seems normal.
Hi,
I have an easy question I believe, I want to log DHCP lease durations
given to clients, I tried the following, however it appears most of the
time, logs are showing half of the lease duration.
log(info, concat( "IP: ", binary-to-ascii(10, 8, ".", leased-address), " ;
", "leasetime:", binary-to-ascii(10,32,"",encode-int(lease-time,32)) ));
subnet 172.16.2.0 netmask 255.255.255.0 {
option routers 172.16.2.1;
pool {
failover peer "failover-partner";
default-lease-time 300;
min-lease-time 300;
max-lease-time 300;
range

172.16https://www.dibbssm.net/GroupFiles/Group167/Documents/Cubs/E1_Cub_Fun_In_the_Snow.pdf.2.10
172.16.2.250;

Post by Denis Laventure
}
}
Oct 2 14:34:44 mercan dhcpd: IP: 172.16.2.127 ; leasetime:155
Oct 2 14:37:10 mercan dhcpd: IP: 172.16.2.127 ; leasetime:154
Oct 2 14:37:13 mercan dhcpd: IP: 172.16.2.127 ; leasetime:297
Oct 2 14:39:37 mercan dhcpd: IP: 172.16.2.127 ; leasetime:156
Oct 2 14:42:03 mercan dhcpd: IP: 172.16.2.127 ; leasetime:154
Oct 2 14:44:28 mercan dhcpd: IP: 172.16.2.127 ; leasetime:155
Oct 2 14:46:53 mercan dhcpd: IP: 172.16.2.127 ; leasetime:155
Oct 2 14:49:18 mercan dhcpd: IP: 172.16.2.127 ; leasetime:155
Oct 2 14:49:54 mercan dhcpd: IP: 172.16.2.127 ; leasetime:264
Oct 2 14:50:47 mercan dhcpd: IP: 172.16.2.127 ; leasetime:247
Oct 2 14:51:18 mercan dhcpd: IP: 172.16.2.127 ; leasetime:269
How can log the precise lease durations, would be great if anyone has any suggestions?
Thanks in advance.
Alp
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https://lists.isc.org/mailman/listinfo/dhcp-users

Alp Eren Kose

2015-10-05 08:09:49 UTC

Permalink

Oh I see, that made it more clear, however I still didn't understand a
point. At renewal time, the client takes another full lease duration right,
so I would still expect to see the full duration?

Perhaps is there anyway that I can log the lease end time or duration at
each request? I know I can get this at the leases file, however I need to
log that.

Thanks a lot,
Alp

Post by Glenn Satchell
Hi Alp
lease-time shows the remaining time in the lease, not the total time.
lease-time
The duration of the current lease - that is, the differ-
ence between the current time and the time that the lease
expires.
regards,
-glenn

;

Post by Denis Laventure
", "leasetime:", binary-to-ascii(10,32,"",encode-int(lease-time,32)) ));
subnet 172.16.2.0 netmask 255.255.255.0 {
option routers 172.16.2.1;
pool {
failover peer "failover-partner";
default-lease-time 300;
min-lease-time 300;
max-lease-time 300;
range

172.16
https://www.dibbssm.net/GroupFiles/Group167/Documents/Cubs/E1_Cub_Fun_In_the_Snow.pdf.2.10
172.16.2.250;

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dhcp-users mailing list
https://lists.isc.org/mailman/listinfo/dhcp-users

Bob Harold

2015-10-05 17:24:49 UTC

Permalink

Post by Denis Laventure
The client will renew the lease at half the max-lease-time. So seeing

150

Post by Denis Laventure
sec for a 300 sec lease seems normal.
Hi,
I have an easy question I believe, I want to log DHCP lease durations
given to clients, I tried the following, however it appears most of the
time, logs are showing half of the lease duration.
log(info, concat( "IP: ", binary-to-ascii(10, 8, ".", leased-address),

" ;

172.16
https://www.dibbssm.net/GroupFiles/Group167/Documents/Cubs/E1_Cub_Fun_In_the_Snow.pdf.2.10
172.16.2.250;

any

Post by Denis Laventure
suggestions?
Thanks in advance.
Alp

Reading the man pages, try replacing:
lease-time
with:
config-option dhcp-lease-time

But do some packet traces to be sure that it truly gives the lease time in
the first ack packet, which might be the mclt instead of the normal lease
time if failover is used.

I would like to try it myself sometime when I get a chance.

--
Bob Harold

Alp Eren Kose

2015-10-07 12:53:40 UTC

Permalink

Thank you very much, I have tried that with no luck. I come accross the
following post from 2007. It seems that it's not possible to log what the
server sends as the lease time duration. People have modified the source to
do that.

https://lists.isc.org/pipermail/dhcp-users/2007-May/003671.html

Post by Alp Eren Kose

On Sun, Oct 4, 2015 at 3:47 PM, Glenn Satchell <

Post by Denis Laventure
The client will renew the lease at half the max-lease-time. So seeing

150

" ;

Post by Denis Laventure
", "leasetime:", binary-to-ascii(10,32,"",encode-int(lease-time,32))

));

Post by Denis Laventure
subnet 172.16.2.0 netmask 255.255.255.0 {
option routers 172.16.2.1;
pool {
failover peer "failover-partner";
default-lease-time 300;
min-lease-time 300;
max-lease-time 300;
range

172.16
https://www.dibbssm.net/GroupFiles/Group167/Documents/Cubs/E1_Cub_Fun_In_the_Snow.pdf.2.10
172.16.2.250;

any

Post by Denis Laventure
suggestions?
Thanks in advance.
Alp

lease-time
config-option dhcp-lease-time
But do some packet traces to be sure that it truly gives the lease time in
the first ack packet, which might be the mclt instead of the normal lease
time if failover is used.
I would like to try it myself sometime when I get a chance.
--
Bob Harold
_______________________________________________
dhcp-users mailing list
https://lists.isc.org/mailman/listinfo/dhcp-users