Proprietary DHCP to ISC DHCP

Keith kwoody at
Wed Nov 14 00:41:08 UTC 2007

We have a proprietary system that we are moving away from that does DHCP
for a small (less than 120 clients) cable system.

The system supplies IP's for the cable modem as well as the client

The proprietary dhcp system hands IP's out in sequential order starting at
number 1, whereas Ive always seen ISC's start at the highest IP (eg. .254)

I have setup a new DHCP server version 3.1 and I'd like to cut over to
this machine.

If an existing modem or client does a DHCPREQUEST to the new server for an
IP it already has, as this is a new server, the lease file is empty
so there are no known leases yet in the leases file, how does the server
handle it?

Will the new server ACK it and write the new lease? Or will it NAK the
REQUEST and send back an OFFER with a different IP?

As the highest IP in use is only about x.x.x.118, even if ISC's dhcp sends
back an OFFER starting at .254 it wont be an issue with conflicts, which
is my primary concern.


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