ISC dhcpd 4.4.1 dhcpd.leases file size and entries age

[Sten Carlsen]

On 18/10/2018 14.49, Simon Hobson wrote:
> Sten Carlsen <stenc at s-carlsen.dk> wrote:
>
>> In general RFC mandates that records be kept so any device can come back and have the same address if available, So my guess is that records from 2014 regards some device that was last attached at that date.
> Indeed, if you have large pools and low client churn, it's quite conceivable that a device from years ago will still have an expired lease in the database. The higher the client churn rate in relation to the pool size, the less age will be seen for expired leases.
What would make an old entry disappear? That its address has been
reused? I did not think that would do it, when the device returns after
years, the same address could be available, so why not use that?
I was thinking that once a lease has been handed out, that device is in
the leases file for ever?
>
> Looking further into the file, it should be found that these expired leases only occur once in the file - ie only active IP addresses should have multiple entries in the file.
This single entry would be written when the leases file is rewritten
about once pr hour.
>
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