I'd like to set up a dhcp server which normally relays to a central site, but has a pool of addresses to hand out if the link to the central site goes down. I'm using isc dhcp server on Debian, but the isc server and relay agent are separate programs, so it seems serving and relaying can't be done in a single binary/configuration.
The setting is a head office/~10 branch network, where it is desirable to run the main servers DHCP servers at head office, so we can grep the logs and get information on all clients. I'd like the branches to get IP addresses even if the link to head office is down, since they may still have internet access and could access some services if so.
My current thinking is I need two devices at each branch, one to run dhcp relay, and the other running non-authoritative dhcp server with a short lease time. (or try to run both on a single machine and bind to different IP addresses?) Otherwise I'll need authoritative servers at each site, and send log information through to head office, but I'd prefer not to go down that track.
All DHCP servers and relays are managed through ansible.
How could I most simply set up a site with DHCP relaying, but with a reserve pool if the main server doesn't respond?
