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DHCP leases + 'wait at shutdown' = trouble


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Here's an interesting problem: On our network, DHCP is normally provided by our Cisco PIX firewall, which serves out addresses with no difficulty. From time to time the PIX DHCP is offline for one reason or another, and we serve DHCP from either a Mac OS X Server or Windows 2000 server. We keep DHCP lease time short (3 hrs) to make the best use of a limited address pool.


Problem is, Mac OS 9 Retrospect clients that are waiting at shutdown for backup (and holding on to their DHCP leases, obviously) seem to be unable to notify the Mac OS X or Windows DHCP server that they are still using the address. This results in the address lease being reallocated to another machine, which of course reports a conflict -- the Mac waiting for backup is still using it. For some reason, the Cisco DHCP server is "more aware" of the clients that are holding on to their addresses (it may be pinging them or portscanning). In the past, a Vicom DHCP server we used was also capable of recognizing these machines and leaving their addresses leased to them -- unfortunately it was unstable for other reasons and has been deprecated.


So, aside from upgrading all the Macs to OS X (we are), setting them not to wait at shutdown (we'll try), raising the DHCP lease time (we could), shutting the machines down each night via a backup (we do, but sometimes they get shut down during the day), expanding our DHCP range via NAT (we will, but it's a lot of work) -- any way to have the software DHCP daemon do a better job of checking for the semiconscious Retrospect-shutdown-hold machines out there?



--Mike Rose

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