I have one branch that connects to HQ via Fiber as a trunk connection. the branch have a user subnet that is unique only to the branch and the gateway is in my HQ core switch vlan interface and also the dhcp server for the users is in the HQ. I have a wireless L3 link between the branch and HQ in case the fiber gets cut. My question is in case the fiber gets cut and the wireless L3 becomes active what is DHCP lease duration i should configure locally in the branch switch because then the main dhcp server will be cut as well? should be too short or something? because if the main link comes back the original dhcp will be connected back """of course then i would have disabled the temporary dhcp""" and I'm worried it might cause conflicts?
There should not be any conflict. The clients continue to use the local switch until the lease expires, once the lease expires and by that time the fiber link is up and running, they will get new IPs from the HQ switch. If you want to make the lease time shorter, so the client switch faster, you can just make it for 8 hours or one day.
but the problem with 8 hours lease is that let us say the fiber link goes down and users get dhcp address from the temporary dhcp for 8 hours and then a minute later fiber goes up and the original dhcp goes up and then other users ask the original dhcp server for an ip address which then it gives them duplicate ip for which the temporary dhcp server has already given as the temporary and original dhcp servers aren't aware of each other pool.
