reuse_lease: lease age logs

[glenn.satchell at uniq.com.au]

This is not de-stabilising your environment, it is improving it.

Most dhcp clients request an update when 50% of the lease time has 
passed. In your case of a one hour lease this would be every 30 minutes. 
But say the client decided to renew after 5 minutes. The dhcp server 
recognises this and responds with the lease information and an expiry 
time of 55 minutes (the remaining time since the lease was originally 
issued). The client now has a lease with 55 minutes remaining, which is 
the exact same amount of time as it would have had, if it didn't renew. 
When 50% of this time passes the client tries to renew again and this 
time get a new one hour lease.

The only difference is that for the early renew the dhcp server did not 
need to go through the full cycle to obtain a new lease, update the 
lease file, etc.

If the client only renews when 50% of the lease has expires you will 
probably never see this. You don't need to do anything about it.

You can adjust this by setting dhcp-cache-threshold in dhcpd.conf. 
Please read the dhcpd.conf man page for details on the setting.

regards,
-glenn

On 2019-10-28 20:08, Surya Teja wrote:
> Hi Glenn
> Thanks for reply but I have few basic doubts,
> when only a small amount of the lease time has passed ---->
> when can we see this type of situation ?
> FYI: The lease time for the scopes is one hour in my config,
> Do I need to add any config statement in dhcpd.conf or increase
> lease-time to stabilize the environment
> 
> Thanks in advance
> 
> On Mon, Oct 28, 2019 at 1:41 PM <glenn.satchell at uniq.com.au> wrote:
> 
>> Hi Surya,
>> 
>> It's a server optimisation for when only a small amount of the lease
>> 
>> time has passed. Rather than go through the whole process to creatge
>> a
>> new lease and update the leases file, the server replies with the
>> existing lease information and the time remaining. It makes no real
>> difference to the client, but for a busy server it can save a lot of
>> I/O
>> and processing as the lease file doesn't need to be updated. It's
>> probably unrelated to the one-lease-per-client setting.
>> 
>> regards,
>> Glenn
>> 
>> On 2019-10-28 18:40, Surya Teja wrote:
>>> Hi
>>> In the log messages of the dhcpd I see few strange messages like
>>> reuse_lease: lease age 173843 (secs) under 25% threshold, reply
>> with
>>> unaltered, existing lease for 192.168.1.6
>>> reuse_lease: lease age 713 (secs) under 25% threshold, reply with
>>> unaltered, existing lease for 192.168.1.81
>>> 
>>> Does any one has any idea what does this reuse lease means ?
>>> Just FYI: I have added a statement one-lease-per-client true; to
>> my
>>> conf recently as i am facing no free lease issues because of
>> roaming
>>> clients, does this impact the environment and cause problem which
>>> leading the above log messages?
>>> 
>>> Thanks in advance
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