Migrating to Failover

[Norman Elton]

I realize this may have been answered before, but I can't seem to find
anything. Feel free to point me to another post...

I've got a single DHCP server serving roughly a dozen subnets. I want
to move this to a new pair of DHCP servers running failover. I'd like
to do this in a controlled manner, one subnet at a time. It's easy to
change the helper-address on a particular subnet, but I somehow need
to migrate the leases to the new pair.

Can I just take the relevant leases from the existing server and
append them to the end of each of the new server's lease file?
Obviously this would need to be done with the server shutdown. I can
tolerate a few minutes outage if necessary. When the servers fire back
up, will it recognize the new lease, even though it doesn't have all
the attributes of a typical failover lease? What happens to the
existing ("free" or "backup") lease already in the file?

Or is there a better way to do what I'm after?

Thanks,

Norman