Mechanism for forcing release of lease from the DHCP server end

[Hillary Nelson]

we've been using similar commands Thomas sent to release leases that know
to be not needed --  our AP subnet lease time is set to 1 week, every once
a while the wireless group order bunch new airports to test and have to
contact us to release lease for them.

Hillary

On Tue, Aug 22, 2017 at 10:17 AM, Thomas Markwalder <tmark at isc.org> wrote:

> Hello Glenn:
>
> You are absolutely right.   Those commands only release the lease in
> terms of the server.
> The client would not be notified of the change as this is not part of
> the protocol.
>
> Thomas
>
>
>
> On 8/22/17 9:50 AM, Glenn Satchell wrote:
> > That series of commands releases the lease in the server, so that the
> > server could then offer it to a different client. However, I don't
> believe
> > there is any part of the DHCP protocol for the server to contact the
> > client and tell it to release the lease. So the original client can
> > continue to use the address until the original lease time expires.
> >
> > If the client did not respond to the ping before offer, the server could
> > then offer the lease to a second client.
> >
> > regards,
> > Glenn Satchell
> >
> > On Tue, August 22, 2017 11:38 pm, Thomas Markwalder wrote:
> >> 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)
> >> Â ==> success
> >> obj: lease
> >> ip-address = b2:10:01:7f
> >> ----------------------------------------------
> >>
> >> 3. Fetch the lease via the open object command
> >> ----------------------------------------------
> >>> open
> >> omapi_set_value (op, 1)
> >> Â ==> success
> >> Â Â  :
> >> Â Â  :
> >> 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)
> >> Â ==> 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)
> >> Â ==> success
> >> omapi_set_value (object, dhcpctl-remote)
> >> Â ==> success
> >> omapi_set_value (handle, 4)
> >> Â ==> success
> >> omapi_set_value (result, 4 18c03fc)
> >> Â ==> 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. Â The client is
> >>> leased the address until a certain expire period. Â There is no way to
> >>> tell the client to stop using the address early.Â
> >>>
> >>> ------------------------------------------------------------
> ------------
> >>>
> >>>     *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
> >>>
> >>>
> > _______________________________________________
> > dhcp-users mailing list
> > dhcp-users at lists.isc.org
> > https://lists.isc.org/mailman/listinfo/dhcp-users
>
>
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