I'm running FreeBSD on a Soekris net4801. It boots from a read-only flash card, and has no permanent writable storage media - only memory disks. It runs several critical network services for me like DNS, and a firewall.

One important service that it does not currently run is a DHCP server. My network has always been made up of a small number of machines with fixed IP addresses, but it's growing, and I'm feeling the need for DHCP. The handbook recommends the net/isc-dhcp3-server port, so that's what I'm looking at installing.

I'm wondering what the implications of not having permanent writable storage will be for the DHCP service. Right now, without DHCP, if I pull the plug out of the wall then restart the box, the network comes right back up with no problems whatsoever. All I lost was some state tables and the DNS cache, which will be rebuilt automatically as needed. Will the DHCP server be this trouble-free if I switch my whole network to dynamic IPs?

When the DHCP server goes offline, then comes back online, what happens?

I'm hoping that the DHCP clients will renew their old leases based on the contents of their /var/db/dhclient.leases files, and that the server will comply with their wishes and repopulate DNS with their names when that happens. However I've read that the server keeps its own dhcpd.leases file. This file will disappear when I restart the server, because it will only exist on a memory disk. What will happen when a client says "you gave me" but the server has no record of this in its dhcpd.leases file?

I suppose a worse scenario would be if the DHCP clients did nothing until their leases expired. They'd be missing from the DNS table for awhile if that happened. Running around and rebooting every machine on the network just because the DHCP server went down for a minute is not something I want to have to do.
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