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Currently we are running a pair of DHCP servers at a medium-sized high school with about a 60/40 split. The problem is that over the years the address reservations have become more and more disorganized. We want to reorganize the address leases so that things are grouped better by type.

The issue arises when we want to move a group of devices from one range of IPs to another, which is already taken by a second group that we want to move to another area, and so on. I was thinking of simply doing the moves slowly, moving a group to an unused area, then shifting things into the hole it left behind, then moving the first group back to where we want it to end up, however this approach is long and tedious, and could lead to several errors and conflicts, if not properly planned.

Is there any better way to do this, avoiding any potential problems that would likely arise?

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This 60/40 split is between two different subnets or different ranges in the same subnet? Are there any DHCP clients that are NOT reservations? Can you list specifically (using fake ranges) your setup? – Daniel Lucas Jun 15 '09 at 17:21
Also, if the servers in the same subnet do they have overlapping scopes and exclusions or are they non-overlapping scopes? – Catherine MacInnes Jun 15 '09 at 17:28
The servers are different ranges in the same subnet and have the same scope. There are some servers and such that have static IPs, but those will be left where they are. – user9564 Jun 15 '09 at 21:34
up vote 1 down vote accepted

Since you are working at a high school, why not use the summer break, and a weekend, to take everything down and rebuild it the way you want it?

You wouldn't actually be unplugging anything. You would be just moving leases.

With most (if not all) your users gone for three months now would be a perfect time. That is assuming you live in an area that observes summer vacation.

My answer still stands even if you have a full user base: move them on the weekend.

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I considered that, then realized that I would have to restart the computers to get the new IPs, and considering how often the users never save their work and leave it open, that could lead to a few issues. Now that I think of it, though, a script could be written to ipconfig /release and /renew on all of them... Thanks. – user9564 Jun 15 '09 at 18:30

If you're using DHCP and you want to clean it all up you have many choices. If you're using private IP addresses you can just move them to different private addrsses in a new DHCP orderly fashion. If you're using public addresses the problem is slightly trickier, but not impossible. The trick is all in lease management. Even if you aren't planning on making the changes soon you can shorten up your leases now, so that they will all churn much faster when the time comes. This is especially important to do early if you have very long lease times.

When your change time comes, Set your leases to a VERY short lease time, like an hour. When the leases expire make sure that the new range you want for the area is in effect there. This will let you roll your DCHP changes over a weekend. The problem is all the machines have to be on for this to work, and your existing leases have to be pretty short. It won't actually require rebooting everything.

As soon as all your machines have refreshed onto new leases in the correct subnets then you can extend your leases back out to something more reasonable for your environment.

This will avoid disruption of users work, as they never notice their own DHCP addresses.

For our campus wide re-iping plan I am have suggested that we move all our IP addresses into a private range for a short while then move them back to where we want them as soon as everyone is over, avoiding the rolling update method you are trying to avoid.

Also reboots DO NOT always cause leases to be checked, or refreshed.

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The shortening of the lease time is a very good idea. Thanks for the suggestion. – user9564 Jun 15 '09 at 21:34

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