Server Move...

Glenn Satchell Glenn.Satchell at
Sun Oct 15 04:02:33 UTC 2006

>Date: Sat, 14 Oct 2006 16:24:21 -0700 (PDT)
>From: Keith Woodworth <kwoody at>
>To: dhcp-users at
>Subject: Re: Server Move...
>On Sat, 14 Oct 2006, Simon Hobson wrote:
>|->>As the new server is starting out with an empty lease file, it will see a
>|->>DISCOVER and pick a lease and hand it out. The problem I have just seen is
>|->>the new server pinged an address, saw that its in use (that client had not
>|->>renewed yet) and abandoned it and gave the DISOVERing client a different
>|->One reason for copying the leases file from the old server, or
>|->alternatively, make the move when as many machines as possible are
>|->switched off.
>|->It does depend on the client though. IIRC, Windows XP clients request
>|->the last address they had when they broadcast for a server and so
>|->would normally get the same address.*
>I tried to figure out how to gracefully copy the lease file from the old
>to the new as I'm moving 4 subnets and doing it one subnet at a
>time. I figured to keep state on the lease file I would have to cherry
>pick all the leases for each subnet from the old lease file and paste
>them into the new lease file.
>Figured it was just as easy to start out with a fresh lease file.

You can copy the whole lease file across. When the dhcp server
starts and reads the lease file it will discard any leases for subnets
it doesn't know about. Likewise it will take the latest version of any
lease, so multiple lease entries will also be handled. It should be as
simple as just copying over the whole file and appending it to whatever
lease file you have on the new server.

In a similar move, when you delete the subnet definition on the old
server and restart dhcp it will also delete all the leases it had for
the old subnet.

So the next time you migrate a subnet you can append the whole lease
file from the old server and it will sort itself out.

Glenn Satchell     mailto:glenn.satchell at | Some days we are
Uniq Advances Pty Ltd | the flies;  some
PO Box 70 Paddington NSW Australia 2021              | days we  are the
tel:0409-458-580  tel:02-9380-6360  fax:02-9380-6416 | windscreens...

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