Mechanism for forcing release of lease from the DHCP server end

[Thomas Markwalder]

Hello all:

It is possible to connect to ISC_DHCP via omshell and change the lease
state to released as
shown below.  The following example you're connecting from the machine
ISC_DHCP
is running on and you didn't specify a key in the server config:


1. Start omshell and connect to ISC DHCP:

---------------------------------------------
centos64 isc_dhcp $ tip/bin/omshell
> server localhost
> port 7911
> connect
obj: <null>
>
----------------------------------------------


2. Create a new lease object and set the ip-address to
the address of the desired lease:
----------------------------------------------
> new lease
obj: lease
> set ip-address=178.16.1.127
omapi_set_value (ip-address, 4 18bed8c)
 ==> success
obj: lease
ip-address = b2:10:01:7f
>
----------------------------------------------

3. Fetch the lease via the open object command
----------------------------------------------
> open
omapi_set_value (op, 1)
 ==> success
   :
   :
obj: lease
ip-address = b2:10:01:7f
state = 00:00:00:02
subnet = 00:00:00:02
pool = 00:00:00:03
hardware-address = 08:00:27:99:72:be
hardware-type = 00:00:00:01
ends = 59:9c:30:bc
starts = 59:9c:2f:90
tstp = 00:00:00:00
tsfp = 00:00:00:00
atsfp = 00:00:00:00
cltt = 59:9c:2f:90
flags = 00
>
----------------------------------------------

4. Set the lease state to FTS_RELEASED (i.e. 4)
----------------------------------------------
set state=4
omapi_set_value (state, 4)
 ==> success
obj: lease
ip-address = b2:10:01:7f
state = 4
subnet = 00:00:00:02
pool = 00:00:00:03
hardware-address = 08:00:27:99:72:be
hardware-type = 00:00:00:01
ends = 59:9c:30:bc
starts = 59:9c:2f:90
tstp = 00:00:00:00
tsfp = 00:00:00:00
atsfp = 00:00:00:00
cltt = 59:9c:2f:90
flags = 00
>
----------------------------------------------


5. Save the change via the update object command:
----------------------------------------------
> update
omapi_set_value (op, 3)
 ==> success
omapi_set_value (object, dhcpctl-remote)
 ==> success
omapi_set_value (handle, 4)
 ==> success
omapi_set_value (result, 4 18c03fc)
 ==> success
obj: lease
ip-address = b2:10:01:7f
state = 4
subnet = 00:00:00:02
pool = 00:00:00:03
hardware-address = 08:00:27:99:72:be
hardware-type = 00:00:00:01
ends = 59:9c:30:bc
starts = 59:9c:2f:90
tstp = 00:00:00:00
tsfp = 00:00:00:00
atsfp = 00:00:00:00
cltt = 59:9c:2f:90
flags = 00
----------------------------------------------

omshell(1) discusses this in general terms.  dhcpd.conf(5) describes how
to configure ISC_DHCP for OMAPI connections.


Regards,

Thomas Markwalder
ISC Software Engineering


On 8/22/17 8:47 AM, perl-list wrote:
> To my knowledge, there is no such method available.  The client is
> leased the address until a certain expire period.  There is no way to
> tell the client to stop using the address early. 
>
> ------------------------------------------------------------------------
>
>     *From: *"Maneesh Kumar" <maneeshk at cdac.in>
>     *To: *dhcp-users at lists.isc.org
>     *Sent: *Tuesday, August 22, 2017 7:47:30 AM
>     *Subject: *Mechanism for forcing release of lease from the DHCP
>     server end
>
>     Dear Members,
>
>     Kindly let me know if there is a mechanism available for forcing
>     release of lease from the DHCP server end.
>
>     If yes, please let me know the way to achieve the same.
>
>
>     Maneesh Kumar
>
>     HPC Infrastructure and Ecosystem Group
>     Centre for Development of Advanced Computing
>
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