Proprietary DHCP to ISC DHCP

[Simon Hobson]

Keith wrote:

>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?

If the requested address is available then it will be given out - ie 
the client will keep it's address provided it asks for it.

>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.

This "starting from the top" is undocumented and liable to change at 
any time without notice - it is purely an artifact of the way the 
tables are managed internally that results in the free address list 
being in reverse order. But once all addresses have been used at 
least once, then the order is determined by the time since each lease 
expired (least recently used first).