dhcpcd-discuss

Hi Matthew

On 01/09/2020 23:47, Matthew Clarkson wrote:
> Hi Roy,
> I switched to testing with master, latest commit is https://roy.marples.name/cgit/dhcpcd.git/commit/?id=c628d4a2a7474f72b99dce03571732667fc0c7b1.
>
> I am still seeing the server offer a different ip address once it comes back online. The dhcpcd output looks like this:
> root@RCFA-0001p:~# dhcpcd --lastleaseextend --nobackground --timeout 10 br0
> dhcpcd-9.1.4 starting
> no such user dhcpcd
> DUID 00:01:00:01:26:3d:a6:3e:00:02:d9:1f:ff:ff
> br0: IAID d9:1f:ff:ff
> br0: rebinding lease of 192.168.10.24
> br0: leased 192.168.10.24 for 471 seconds
> br0: adding route to 192.168.10.0/24
> br0: adding default route via 192.168.10.1
> br0: failed to renew DHCP, rebinding
> br0: DHCP lease expired, extending lease
> br0: soliciting a DHCP lease
> br0: offered 192.168.10.25 from 192.168.10.2
> br0: probing address 192.168.10.25/24
> br0: leased 192.168.10.25 for 600 seconds
> br0: changing route to 192.168.10.0/24
> br0: changing default route via 192.168.10.1
>
> Thanks.

I don't see this as a dhcpcd problem.

From the servers perspective your lease has expired - for example it might have 
handed 192.168.10.24 to another host.

I think ISC DHCP server keeps records of who had what ip address after expiry 
and only re-uses these once the pool of available addresses is exhausted and 
then oldest first. In this situation you would still get 192.168.10.24 if it's 
still available.

dnsmasq on the other hand i think purges the record when it expires so it will 
hand it out quite happily to another host.

What you are really asking for is to request an infinite lease time where your 
address is guaranteed by the server never to change.
You can do this by setting `leasetime 4294967295` in dhcpcd.conf which 
represents infinity in DHCP terms.
I've comitted a patch to allow `leasetime -1` which is easier to comprehend as 
infinity.
https://roy.marples.name/cgit/dhcpcd.git/commit/?id=2d3b623273de0dd2ce30e79af12953aa6f0f8a25

However, most servers will reject this request and give you real leasetime which 
will expire at some point.

Another option is to use INFORM to inform the DHCP server of your IP address 
rather than lease it.

Roy