DHCP leases issue

[Thomas Markwalder]

If you're clients are roaming between networks and are not releasing 
leases you may wish to use this flag:


The /one-lease-per-client/ statement

*one-lease-per-client* /flag/*;*

If this flag is enabled, whenever a client sends a DHCPREQUEST for a 
particular lease, the server will automatically free any other leases 
the client holds. This presumes that when the client sends a 
DHCPREQUEST, it has forgotten any lease not mentioned in the DHCPREQUEST 
- i.e., the client has only a single network interface /and/ it does not 
remember leases it’s holding on networks to which it is not currently 
attached. Neither of these assumptions are guaranteed or provable, so we 
urge caution in the use of this statement.



On 9/6/19 11:47 PM, Surya Teja wrote:
> Hi Bill,
>
> Thanks for reply as suggested i have increased lease time to one hour 
> and I observerd one more scenario when the client moves from one 
> subnet to another subnet ( lease time say 1hr). The client got IP from 
> the second subnet scope but the previous IP in the 1st subnet is still 
> in hold and in the lease file. It still recorded an active entry. How 
> can the dhcp server reclaims those unused IP's? Do we have any 
> configuration statement making dhcp to cross check all the active IP's 
> of that scope before saying no free leases.
> The first IP is getting into free state after completing its 1 hour 
> lease duration till that time it is active mode only.
>
> Thanks in advance.
>
> On Sat, 7 Sep 2019, 00:33 Bill Shirley, 
> <bill at c3po.polymerindustries.biz 
> <mailto:bill at c3po.polymerindustries.biz>> wrote:
>
>     Note: two minutes (120 seconds) is a very short lease time.
>
>     Are you sure you're looking at the correct lease file?  Your grep
>     says you have *no**
>     **leases* on 192.168.3.x.
>
>     Your log entries via looks strange.  I would think it should
>     contain the interface name:
>     DHCPDISCOVER from 40:4e:36:d2:bf:9d via wifi
>     DHCPDISCOVER from b4:18:d1:69:02:f9 (Bobs-iPhone) via wifi
>
>     Bill
>
>     On 9/6/2019 6:25 AM, Surya Teja wrote:
>>     Hi
>>     I have configured the dhcp on my local environment with the
>>     configuration as
>>     =================================
>>     subnet 192.168.3.0 netmask 255.255.255.0 {
>>             pool {
>>                     range 192.168.3.3 192.168.3.143;
>>             }
>>                     default-lease-time 120;
>>                     max-lease-time 120;
>>                     option domain-name "example.com
>>     <http://example.com>";
>>                     option routers 192.168.3.1;
>>                     option subnet-mask 255.255.255.0;
>>             }
>>     But no client is able to get the IP and in the logs I can see:
>>     DHCPDISCOVER from 84:EF:18:6A:89:DE via 192.168.3.11
>>     <http://192.168.3.11>: network 192.168.3.0/24
>>     <http://192.168.3.0/24>:*no free leases*
>>     DHCPDISCOVER from 00:FF:4A:81:D5:A5 via 192.168.3.16
>>     <http://192.168.3.16>: network 192.168.3.0/24
>>     <http://192.168.3.0/24>: *no free leases*
>>     But it is not possible and none of the client get the lease from
>>     the specified network. I cross checked in the lease file also
>>     [root at dhcpserver]# cat dhcpd.leases | grep 192.168.3 -A 10 -B 10
>>     [root at dhcpserver]#
>>     It doesn't shows any entry
>>
>>     Any help is appreciated thanks in advance
>>
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