dhcpcd-discuss

Hi Mathew

On 28/08/2020 01:05, Matthew Clarkson wrote:
> Hello,
>
> We are looking at using this dhcpcd project as the dhcp client in a new 
> product, and we are trying to match the behaviour of an older client in 
> an older product. The version we are looking at is 8.1.9.
>
> The specific case we are looking at is when the dhcp server goes 
> offline. We would like to see the device attempt to rediscover and if 
> the server doesn’t respond then bind to the previous address for a short 
> period of time, and repeat until the server is back.
>
> As I understand, this is similar to –lastleaseextend except that 
> lastleaseextend is using the full lease time of the last received lease. 
> The concern is that if the server is offline temporarily or moved, maybe 
> to change the ip subnet, then it could take a long time for the device 
> to resync.
>
> As an example, if the device previously received a lease for 
> 192.168.10.18 (leasetime 2 hours) and on the next rebind attempt the 
> device would look like:
>
> <server offline>
>
> 192.168.10.18 -> 255.255.255.255 DHCP Request
>
> <no response>
>
> 0.0.0.0-> 255.255.255.255 DHCP Discover
>
> <no response>
>
> <2 minutes later>
>
> 0.0.0.0-> 255.255.255.255 DHCP Discover
>
> <repeat>
>
> Instead it looks like:
>
> 192.168.10.18 -> 255.255.255.255 DHCP Request
>
> <no response>
>
> <2 hour later>
>
> 0.0.0.0 -> 255.255.255.255 DHCP Request
>
> Is there another option which will behave as we are expecting, or are 
> there options to modify the behaviour of lastleaseextend (such as 
> setting a shorter lease time for the extension)?

Looks like a bug to me.
With lastlease and lastleaseextend there is still supposed to be 
periodic DHCP requests upto a maximum of 60 seconds + ramdomisation 
intervals.

I'm currenty on holiday and have a small backlog of issues to work 
through, but I'll try and give a better answer with a patch sometime 
next week.

Roy