Server Move...

Keith Woodworth kwoody at
Sat Oct 14 23:24:21 UTC 2006

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.

Its a DSL network so best I can do is make the change at 4 am or something
next time.

|->When the transition is complete, remove the abandoned leases from the
|->leases file, that will free up the addresses. You can leave them
|->there and they will be reclaimed in required, but it will increase
|->address churn in the subnet.

There are only 5 abandoned leases and I still have a large (100+) pool of
free IP's in this subnet of about 200 users so that should not become an

|->Abandoned leases are the lowest priority when allocating new leases,
|->so expired leases will be reallocated in preference - thus reducing
|->the likelyhood of a client returning and getting it's old address.

Thanks for the info on that.

|->>I do have much larger subnets than active clients so I'm hoping that will
|->>help too.
|->It will

I thought so.

|->- it just kept assigning itself a 'link local' address. I assumed
|->there was a problem with the VLAN setup until I plugged in my Mac and
|->got an address straight away.
|->It turned out that their DHCP server was not acting authoratatively
|->and didn't respond with a NACK when the client requested it's link
|->local address - so the client never stopped using it, and never got a
|->real address. I had to manually assign it an address in the correct
|->range then set it back to DHCP to make it work !

Ah-ha! My earlier question about authoritative comes back. I have made
sure the DHCP server is authoritative for all the different
networks/subnets it hands out leases for. It was before, but have updated
my configs and moved that statement around to the global section.

Its a small town and its somewhat common for a computer to move around in
town and suddenly be coming in from another part of the DSL network,
wanting its old lease, but gets NAK'd instead.


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