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Re: strange DHCP behaviour [SOLVED]

From tony <lists@vanderhoff.org>
Newsgroups linux.debian.user
Subject Re: strange DHCP behaviour [SOLVED]
Date 2018-10-24 14:40 +0200
Message-ID <wMqC6-2gz-5@gated-at.bofh.it> (permalink)
References <wM5Hj-6JR-11@gated-at.bofh.it> <wMkQ1-7lk-3@gated-at.bofh.it> <wMpwl-1Ej-3@gated-at.bofh.it> <wMpG2-1IE-5@gated-at.bofh.it>
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On 24/10/2018 13:34, john doe wrote:
> On 10/24/2018 1:28 PM, tony wrote:
>> On 24/10/2018 08:19, Reco wrote:
>>> 	Hi.
>>>
>>> On Tue, Oct 23, 2018 at 03:56:34PM +0200, Tony van der Hoff wrote:
>>>> The DHCP server is another Stretch system, with the stanzas
>>>> host tony-lt {
>>>> 	hardware ethernet 0c:60:76:6c:e6:6f;
>>>> 	fixed-address 192.168.1.199;
>>>> 	}
>>>> subnet 192.168.1.0 netmask 255.255.255.0
>>>> 	{
>>>>         range 192.168.1.200 192.168.1.254;
>>>>         option routers 192.168.1.10;
>>>> 	}
>>>>
>>>> That MAC is correct for the laptop.
>>>>
>>>
>>>> Finally, the server shows:
>>>> Oct 23 14:23:38 routerpi dhcpd[1068]: DHCPREQUEST for 192.168.1.253 from
>>>> 0c:60:76:6c:e6:6f (tony-lt) via eth0
>>>> Oct 23 14:23:38 routerpi dhcpd[1068]: DHCPACK on 192.168.1.253 to
>>>> 0c:60:76:6c:e6:6f (tony-lt) via eth0
>>>> Oct 23 14:23:53 routerpi dhcpd[1068]: reuse_lease: lease age 15 (secs)
>>>> under 25% threshold, reply with unaltered, existing lease for 192.168.1.253
>>>> Oct 23 14:23:53 routerpi dhcpd[1068]: DHCPREQUEST for 192.168.1.253 from
>>>> 0c:60:76:6c:e6:6f (tony-lt) via eth0
>>>> Oct 23 14:23:53 routerpi dhcpd[1068]: DHCPACK on 192.168.1.253 to
>>>> 0c:60:76:6c:e6:6f (tony-lt) via eth0
>>>>
>>>> So, my question: why is the server handing out .253, when it is
>>>> configured to provide .199?
>>>
>>> Because client specifically asks for .253 address:
>>>
>>>> Oct 23 14:23:38 routerpi dhcpd[1068]: DHCPREQUEST for 192.168.1.253 from
>>>> 0c:60:76:6c:e6:6f (tony-lt) via eth0
>>>
>>
>> Agree fully.
>>
>>> And, to quote dhcpd.conf:
>>>
>>> There may be a host declaration matching the client’s identification. If
>>> that host declaration contains a fixed-address declaration that lists an
>>> IP address that is valid for the network segment to which the client is
>>> connected. In this case, the DHCP server will never do dynamic address
>>> allocation. In this case, the client is required to take the address
>>> specified in the host declaration. If the client sends a DHCPREQUEST for
>>> some other address, the server will respond with a DHCPNAK.
>>>
>>
>> Yes, agree again.
>>
>>> When the DHCP server allocates a new address for a client (remember,
>>> this only happens if the client has sent a DHCPDISCOVER), it first looks
>>> to see if the client already has a valid lease on an IP address, or if
>>> there is an old IP address the client had before that hasn’t yet been
>>> reassigned. In that case, the server will take that address and check it
>>> to see if the client is still permitted to use it. If the client is no
>>> longer permitted to use it, the lease is freed if the server thought it
>>> was still in use - the fact that the client has sent a DHCPDISCOVER
>>> proves to the server that the client is no longer using the lease.
>>>>
>>> You assume that a 'host' entry overrides any previous IP assignment.
>>> It's not.
>>>
>>
>> No, When a client issues a DHCPREQUEST which the server doesn't like,
>> the server should issue a DHCPNAK, to which the client will respond with
>> a DHCPDISCOVER. The server is not sending the NAK. This, I believe to be
>> the crux of the matter. The 'host' assignment should cause the server to
>> send a DHCPNAK.
>>
>>>
>>>> What is this 'reuse-lease' all about?
>>>
>>> Your DHCP client renews the leased IP although the lease time is not
>>> expired. Not relevant to this problem.
>>>>
>>>> I've tried 'dhclient -r wlan 0; dhclient -v wlan0' on the laptop, to no
>>>> avail.
>>>
>>> I'd be really surprised if it did change something. Your DHCP server has
>>> a problem, client does not.
>>>
>>
>> I agree again, but when one gets desperate, one starts to grasp at straws.
>>
>>>
>>>> Any suggestions, please?
>>>
>>> Clear your DHCP lease file on DHCP server. Bounce the thing. Check
>>> again.
>>>
>>
>> Yes, I've done that. No change I'm afraid.
>>
> 
> By doing:
> 
> $ systemctl stop isc-dhcp-server
> rm /var/lib/dhcpd/dhcpd.leases
> $ systemctl start isc-dhcp-server
> 
> Make sure that the client is disconnected before doing the above.
> 

Ew, this time it worked. I wonder why deleting the leases file was
better than clearing it out?

Ah, well; thank you all for your help.

Cheers, Tony

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Thread

strange DHCP behaviour Tony van der Hoff <tony@vanderhoff.org> - 2018-10-23 16:20 +0200
  Re: strange DHCP behaviour Roberto C. Sánchez <roberto@debian.org> - 2018-10-23 16:30 +0200
    Re: strange DHCP behaviour tony <lists@vanderhoff.org> - 2018-10-23 18:10 +0200
  Re: strange DHCP behaviour Martin <keine-eile@online.de> - 2018-10-23 17:20 +0200
    Re: strange DHCP behaviour tony <lists@vanderhoff.org> - 2018-10-23 18:00 +0200
    Re: strange DHCP behaviour john doe <johndoe65534@mail.com> - 2018-10-23 18:40 +0200
      Re: strange DHCP behaviour john doe <johndoe65534@mail.com> - 2018-10-23 19:50 +0200
        Re: strange DHCP behaviour john doe <johndoe65534@mail.com> - 2018-10-23 20:10 +0200
          Re: strange DHCP behaviour tony <lists@vanderhoff.org> - 2018-10-24 10:40 +0200
      Re: strange DHCP behaviour tony <lists@vanderhoff.org> - 2018-10-23 19:50 +0200
  Re: strange DHCP behaviour mick crane <mick.crane@gmail.com> - 2018-10-23 21:10 +0200
    Re: strange DHCP behaviour tony <lists@vanderhoff.org> - 2018-10-24 10:50 +0200
      Re: strange DHCP behaviour mick crane <mick.crane@gmail.com> - 2018-10-24 12:20 +0200
        Re: strange DHCP behaviour tony <lists@vanderhoff.org> - 2018-10-24 12:40 +0200
          Re: strange DHCP behaviour mick crane <mick.crane@gmail.com> - 2018-10-24 13:00 +0200
            Re: strange DHCP behaviour tony <lists@vanderhoff.org> - 2018-10-24 13:20 +0200
  Re: strange DHCP behaviour deloptes <deloptes@gmail.com> - 2018-10-23 22:00 +0200
    Re: strange DHCP behaviour tony <lists@vanderhoff.org> - 2018-10-24 11:00 +0200
  Re: strange DHCP behaviour Reco <recoverym4n@enotuniq.net> - 2018-10-24 08:30 +0200
    Re: strange DHCP behaviour tony <lists@vanderhoff.org> - 2018-10-24 13:30 +0200
      Re: strange DHCP behaviour john doe <johndoe65534@mail.com> - 2018-10-24 13:40 +0200
        Re: strange DHCP behaviour [SOLVED] tony <lists@vanderhoff.org> - 2018-10-24 14:40 +0200
          Re: strange DHCP behaviour [SOLVED] <tomas@tuxteam.de> - 2018-10-24 14:50 +0200
            Re: strange DHCP behaviour [SOLVED] tony <lists@vanderhoff.org> - 2018-10-25 14:50 +0200
          Re: strange DHCP behaviour [SOLVED] Michael Stone <mstone@debian.org> - 2018-10-24 17:00 +0200

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