[Dnsmasq-discuss] Howto reclaim all dhcp leases after router reboot

[Tuxo]

Hi Matus,

Thanks for replying so quickly to my request.

On 25.09.20 11:39, Matus UHLAR - fantomas wrote:

> 
> why the need to reclaim them?
> 

Because I like to have a place (file) where I can see what leases have 
been given out, to what IP address and what hostname is currently using 
them.

It's all dynamically assigned, so it can change depending on what new 
devices show up like mobile phones or tablets and what devices have 
already left - some of them without properly signing off to the router.

I simply don't know a better way except monitoring syslog, which is more 
cumbersome than just checking a single file with all the current leases 
in it.

> 
> that's because the lease file is stored in /tmp , which resides on 
> transient filesystem on most routers, The filesystem gets empty and dhcp server 
> has no idea who used what IPs before.
> 

Yes, that is true and I indeed completely forgot about that! If I change 
it back to /var/lib/misc/dnsmasq.leases the file will survive a shutdown.

I hope dnsmasq will eventually clean up the "dead" leases from all the 
devices that forgot to send a proper dhcp release request before the 
client shuts down. IIRC all my Windows machines and my tablets forget to 
do it.

I assume inactive devices will remain listed until the lease time 
expires? If not, I end up with an untidy lease file, where most of the 
entries are no longer actively in use. That would render the file 
useless. I'll have to check that thoroughly, probably best to keep the 
lease time short then.

Thanks, I guess that solves my issue for now, otherwise I'll report back 
with new questions.

Regards,

Tuxo